What governs the reaction center excitation wavelength of photosystems I and II?

The sun’s spectrum harvested through photosynthesis is the primary source of energy for life on earth. Plants, green algae, and cyanobacteria—the major primary producers on earth—utilize reaction centers that operate at wavelengths of 680 and 700 nm. Why were these wavelengths “chosen” in evolution? This study analyzes the efficiency of light conversion into chemical energy as a function of hypothetical reaction center absorption wavelengths given the sun’s spectrum and the overpotential cost associated with charge separation. Surprisingly, it is found here that when taking into account the empirical charge separation cost the range 680–720 nm maximizes the conversion efficiency. This suggests the possibility that the wavelengths of photosystem I and II were optimized at some point in their evolution for the maximal utilization of the sun’s spectrum.     

Question 1: Origin of Life and the Living State

The aim of this article is to discuss four topics: First, the origin of molecular reproduction. Second, the origin of agency – the capacity of a system to act on its own behalf. Agency is a stunning feature of human and some wider range of life. Third, to discuss a still poorly articulated feature of life noticed by the philosopher Immanuel Kant over 200 years ago: A self propagating organization of process. We have no theory for this aspect of life, yet it is central to life. Fourth, I will discuss constraints, as in Schroedinger’s aperiodic crystal (Schroedinger E, What is life? The physical aspect of the living cell, 1944), as information, part of the total non-equilibrium union of matter, energy, work, work cycles, constraints, and information that appear to comprise the living state.     

Effect of herbivory on the growth and photosynthesis of replanted Calligonum caput-medusae saplings in an infertile arid desert

Replanted Calligonum caput-medusae saplings in the Tarim River watershed face short-term and frequent herbivory by goats, which can result in either growth inhibition or stimulation. The effects of herbivory on shrub saplings are unclear. We simulated herbivory with clipping to test two hypotheses. We hypothesized that (1) moderate herbivory may positively affect replanted shrub saplings due to overcompensatory growth and compensatory photosynthesis and that (2) high amounts of defoliation may change water availability and impair photosynthesis and growth of saplings. We applied four defoliation treatments (0, 30, 50, and 70 %) to 2-year-old C. caput-medusae saplings to test the effects of herbivory. Moderately defoliated (~30 %) saplings grew faster and had higher photosynthetic performance than controls; however, defoliation of 50 % or more reduced growth due to undercompensatory photosynthesis and reduced water availability. Non-photochemical quenching by thermal dissipation provided photoprotection when absorbed light energy used in PSII photochemistry was inhibited, reducing excess excitation energy and allowing saplings with high amounts of defoliation to maintain adequate photosystem functioning. This suggests that moderate herbivory of replanted shrubs used as forage in arid ecological restoration projects is feasible, but that uncontrolled grazing should be forbidden.     

The many states of aging: a meeting and some demographic aspects

With an expectation of life at birth of 27 years in the middle of the 18th century, 21% of males reached their 60th birthday with a remaining expectation of life of 12 years. Under the conditions of mortality of 1950, in France, 70 percent could celebrate their 60th birthday, and they had still 15 years (only) to live on the average. This last figure started increasing after 1950: the expectancy of life at age 60 is now over 20 years, and it will exceed 25 years around 2050 (for women, the mean will be 31 years). Longevity is an individual capacity. It is now increasing fast, and becomes more and more responsible for the ageing of the population (the rise in the proportion of older persons in the population). We now try to forecast the number of centenarians, and even of super-centenarians (aged 110 years and more), and speculate about the maximum life span. We are in fact entering an entirely new era, when three, four, even five generations can survive simultaneously. Are we prepared to it? The French Ministers for Research and for Social affairs set up a Committee of 15 members (chaired by Henri Leridon) to prepare a National Meeting of Researchers on Ageing, in order to review the situation of research in France on this issue and to make proposals for organising and orienting new studies. The life span of human species, as well as the one of individuals, is undoubtedly depending upon genetic factors. But interactions with environmental factors and with behaviour also play a major role. To be able to disentangle these complex associations, it will be necessary to combine the work of biologists, clinicians and social sciences specialists. The main conclusions of the June 2001 meeting are reported here, together with some orientations of demographic research on mortality at oldest ages and the limits of longevity.     

Darwin's principles of divergence and natural selection: Why Fodor was almost right

Darwin maintained that the principles of natural selection and divergence were the “keystones” of his theory. He introduced the principle of divergence to explain a fundamental feature of living nature: that organisms cluster into hierarchical groups, so as to be classifiable in the Linnaean taxonomic categories of variety, species, genus, and so on. Darwin’s formulation of the principle of divergence, however, induces many perplexities. In his Autobiography, he claimed that he had neglected the problem of divergence in his Essay of 1844 and only solved it in a flash during a carriage ride in the 1850s; yet he does seem to have stated the problem in the Essay and provided the solution. This initial conundrum sets three questions I wish to pursue in this essay: (1) What is the relationship of the principle of divergence to that of natural selection? Is it independent of selection, derivative of selection, or a type of selection, perhaps comparable to sexual selection? (2) What is the advantage of divergence that the principle implies—that is, why is increased divergence beneficial in the struggle for life? And (3) What led Darwin to believe he had discovered the principle only in the 1850s? The resolution of these questions has implications for Darwin’s other principle, natural selection, and permits us to readjust the common judgment made about Jerry Fodor’s screed against that latter principle.     

Evolution of the Z-scheme of photosynthesis: a perspective

The concept of the Z-scheme of oxygenic photosynthesis is in all the textbooks. However, its evolution is not. We focus here mainly on some of the history of its biophysical aspects. We have arbitrarily divided here the 1941–2016 period into three sub-periods: (a) Origin of the concept of two light reactions: first hinted at, in 1941, by James Franck and Karl Herzfeld; described and explained, in 1945, by Eugene Rabinowitch; and a clear hypothesis, given in 1956 by Rabinowitch, of the then available cytochrome experiments: one light oxidizing it and another reducing it; (b) Experimental discovery of the two light reactions and two pigment systems and the Z-scheme of photosynthesis: Robert Emerson’s discovery, in 1957, of enhancement in photosynthesis when two light beams (one in the far-red region, and the other of shorter wavelengths) are given together than when given separately; and the 1960 scheme of Robin Hill & Fay Bendall; and (c) Evolution of the many versions of the Z-Scheme: Louis Duysens and Jan Amesz’s 1961 experiments on oxidation and reduction of cytochrome f by two different wavelengths of light, followed by the work of many others for more than 50 years.     

Long-distance translocation of photosynthates: a primer

The storage of light energy in chemical form through photosynthesis is the key process underlying life as we know it. To utilize photosynthates efficiently as structural materials or as fuel to drive endergonic processes, they have to be transported from where they are produced to where they are needed. In this primer, we provide an overview of basic biophysical concepts underlying our current understanding of the mechanisms of photosynthate long-distance transport, and briefly discuss current developments in the field.     

Ouderen met een verstandelijke beperking verliezen veel zelfredzaamheid gedurende drie jaar: resultaten van de Gezond Ouder studie (GOUD)

The responsibilities for the care of a significant portion of the population with an intellectual disability (ID) were recently transferred from the government to the municipalities. It is therefore important that policymakers and care professionals know how much support this population needs in their daily life. Therefore, this study focuses on the decline in daily functioning of older adults with ID (≥50 years, n = 703) over 3 years, and if daily functioning is a predictor for all-cause mortality. Daily functioning was operationalized as basic and instrumental activities of daily living (ADL and IADL) and mobility. Fifty-five percent of the total group declined in ADL, 42?% in IADL, and 38?% in mobility. Thirty-nine percent of the participants with mild ID declined in ADL, 55?% in IADL, and 27?% in mobility. Poor daily functioning and mobility was a risk factor for all-cause mortality. This epidemiological study shows a clear decline in the daily functioning of older adults with intellectual disabilities over a 3-year follow-up period. Care providers should be aware of this decline and focus on maintaining as much independence as possible.     

Aging and shift work: a complex problem to face

The baby boomer generation is well into the 50+ age bracket, making it one of the largest demographic age cohorts. Whereas this cohort would have previously considered retirement, the evidence suggests that it will remain in the workforce for a longer period in response to a number of social and economic drivers. Mandatory retirement has either been abolished or is under consideration. An increased and healthier life expectancy means that people may work longer for financial and/or psychological reasons. In addition, a global shortage of skilled labor will result in efforts to keep employees in the workplace for longer periods. These trends have a number of implications for working time. What are the health implications of an aging workforce? How do we sustain good work ability into the latter years? What do we know about aging and shift work? What actions are required in the workplace to assist aging workers? This paper is not a comprehensive review of the literature but serves to highlight the complexities in understanding the relationship between shift work and aging. We discuss aging and human function and, in particular, the impact of aging on the circadian system. In addition, we outline new policy directions in this area and raise several suggestions to assist the well-being of aging workers.     

Aging and Shift Work: A Complex Problem to Face

The baby boomer generation is well into the 50+ age bracket, making it one of the largest demographic age cohorts. Whereas this cohort would have previously considered retirement, the evidence suggests that it will remain in the workforce for a longer period in response to a number of social and economic drivers. Mandatory retirement has either been abolished or is under consideration. An increased and healthier life expectancy means that people may work longer for financial and/or psychological reasons. In addition, a global shortage of skilled labor will result in efforts to keep employees in the workplace for longer periods. These trends have a number of implications for working time. What are the health implications of an aging workforce? How do we sustain good work ability into the latter years? What do we know about aging and shift work? What actions are required in the workplace to assist aging workers? This paper is not a comprehensive review of the literature but serves to highlight the complexities in understanding the relationship between shift work and aging. We discuss aging and human function and, in particular, the impact of aging on the circadian system. In addition, we outline new policy directions in this area and raise several suggestions to assist the well‐being of aging workers.     

Engine of Life and Big Bang of Evolution: A Personal Perspective

Photosystem II (PS II) is the engine for essentially all life on our planet and its beginning 2.5 billion years ago was the 'big bang of evolution.' It produces reducing equivalents for making organic compounds on an enormous scale and at the same time provides us with an oxygenic atmosphere and protection against UV radiation (in the form of the ozone layer). In 1967, when I began my career in photosynthesis research, little was known about PS II. The Z-scheme had been formulated [Hill and Bendall (1960) Nature 186: 136–137] and Boardman and Anderson [(1964) Nature 203: 166–167] had isolated PS II as a discrete biochemical entity. PS II was known not only to be the source of oxygen but of variable chlorophyll fluorescence [Duysens and Sweers (1963) In: Studies on Microalgae and Photosynthetic Bacteria, pp. 353–372. University of Tokyo Press, Tokyo] and delayed chlorophyll fluorescence [Arnold and Davidson (1954) J Gen Physiol 37: 677–684]. P680 had just been discovered [Döring et al. (1967) Z Naturforsch 22b: 639–644]. No wonder the 'black box of PS II' was described at that time by Bessel Kok and George Cheniae [Current Topics in Bioenergetics 1: 1–47 (1966)] as the 'inner sanctum of photosynthesis.' What a change in our level of understanding of PS II since then! The contributions of many talented scientists have unraveled the mechanisms and structural basis of PS II function and we are now very close to revealing the molecular details of the remarkable and thermodynamically demanding reaction which it catalyzes, namely the splitting of water into its elemental constituents. It has been a privilege to be involved in this journey.     

Light-driven quinone reduction in heliobacterial membranes

Vyacheslav Vasilevich (V.V.) Klimov (or Slava, as most of us called him) was born on January 12, 1945 and passed away on May 9, 2017. He began his scientific career at the Bach Institute of Biochemistry of the USSR Academy of Sciences (Akademy Nauk (AN) SSSR), Moscow, Russia, and then, he was associated with the Institute of Photosynthesis, Pushchino, Moscow Region, for about 50 years. He worked in the field of biochemistry and biophysics of photosynthesis. He is known for his studies on the molecular organization of photosystem II (PSII). He was an eminent scientist in the field of photobiology, a well-respected professor, and, above all, an outstanding researcher. Further, he was one of the founding members of the Institute of Photosynthesis in Pushchino, Russia. To most, Slava Klimov was a great human being. He was one of the pioneers of research on the understanding of the mechanism of light energy conversion and of water oxidation in photosynthesis. Slava had many collaborations all over the world, and he is (and will be) very much missed by the scientific community and friends in Russia as well as around the World. We present here a brief biography and some comments on his research in photosynthesis. We remember him as a friendly and enthusiastic person who had an unflagging curiosity and energy to conduct outstanding research in many aspects of photosynthesis, especially that related to PSII.     

Joan Heath interviews Suzanne Cory and Joan Steitz: a female perspective of science in the swinging ‘60s

Prompted by the occasion of International Women''s Day, Joan Heath and DMM reunited Professors Suzanne Cory and Joan Steitz via Zoom to discuss their extraordinary careers and joint experiences in science. They also delve into past and present challenges for women in science, and discuss the role of scientists in a post-pandemic world.

Suzanne Cory, Joan Steitz and Joan Heath (from left to right) As one of Australia''s most eminent molecular biologists, with a school in Melbourne bearing her name, Professor Suzanne Cory has been both Director of The Walter and Eliza Hall Institute of Medical Research in Australia (WEHI) and President of the Australian Academy of Science. She earned her PhD at the Medical Research Council (MRC) Laboratory of Molecular Biology (LMB) in Cambridge, UK, with postdoctoral training at the University of Geneva. She continues her research at WEHI as an honorary distinguished research fellow, investigating the genetics of the immune system in the development of blood cancers and the effects of chemotherapeutic drugs on cancer cells.Joan Steitz – currently Sterling Professor of Molecular Biophysics and Biochemistry at Yale University, and for 35 years the recipient of a Howard Hughes fellowship – is best known for her seminal work in RNA biology. She was the first female graduate student to join the laboratory of James Watson at Harvard University and proceeded with her postdoctoral training at the MRC LMB in Cambridge. Her pioneering research delved into the fundamental mechanisms of ribosome and messenger RNA interactions, as well as RNA splicing, heralding the phenomenon of alternative RNA splicing. A recipient of many awards and honours, she is also involved in international projects aimed at supporting women in science.Host Joan Heath heads a laboratory at WEHI in Australia. She received her undergraduate degree from the University of Cambridge, followed by her PhD at the Strangeways Research Laboratory also in Cambridge, then just across the road from the MRC LMB. After postdoctoral positions in bone biology and osteoporosis research, Joan joined the Ludwig Institute for Cancer Research where she became a laboratory head, and changed her focus to cancer research using zebrafish to identify genes that are indispensable for the rapid growth and proliferation of cells during development. She joined the WEHI in 2012. There she showed that the same developmental genes are also required by highly proliferative, difficult-to-treat cancers, including lung, liver and stomach cancer, paving the way for translational research targeting these genes in novel cancer therapies. Joan H: How long have you two known each other? Suzanne: I was calculating that this morning and I was astonished because it seems like only yesterday, but it has been 55 years since we met in Cambridge. It has been a voyage in science and a voyage in the world because we have always made a point to meet up in beautiful places and go hiking. That is how we''ve been able to renew our friendship over all these years. Joan H: Where were you when you first met? Joan S: We both were working at the MRC LMB in Cambridge, England. Suzanne was doing her PhD and I arrived slightly later for a postdoc.Suzanne: We had a pre-meeting in the sense that Joan, Jerry Adams (my future husband) and Tom Steitz (Joan''s husband), were all graduate students together in Harvard. So, when Joan and Tom came to Cambridge, it was natural that we would all start doing things together. And Joan and I ended up sharing a lab bench.Joan S: The reason that I did a postdoc in the mecca of X-ray crystallography was that I had married a crystallographer – and there was no other place that he could possibly go. They very much wanted to have my husband at the Cambridge MRC lab, but there wasn''t a clear plan for me. Francis Crick suggested that I do a literature project in the library, but I knew that theory was not my forte in comparison to experiments. I started talking to the many people working in the lab and found a project that no one wanted, because it was so challenging. But it was a very interesting problem, so I decided to take it on – and it turned out to be a great project.Joan H: That''s amazing. You were obviously determined to overturn other people''s expectations of you.Suzanne, even now, it''s extremely unusual for a young person to leave their home country to do their PhD. It''s still a brave thing to do but all those years ago it was really courageous. You told me that you ended up there because you wrote a simple letter, which was a complete shot in the dark.Suzanne: It certainly was. During my master''s degree at the University of Melbourne, I became more and more interested in doing science and decided I would do a PhD. But I had a counteracting desire to travel and see Europe. So I decided that I would do my PhD overseas to give myself the opportunity of travelling. I had fallen in love with DNA during my undergraduate studies. So, I wrote a letter to Francis Crick in Cambridge, and asked if he would take me on as a PhD student. Much to my amazement, I eventually got a letter back saying yes. I think that my professor of biochemistry might have also visited Cambridge while he was travelling and spoken up for me. However, I was still extraordinarily fortunate that Francis had agreed because there weren''t many PhD students in the LMB at that time. It made such a difference to my entire life. I look back on that letter and think, “How did you have the audacity to write that letter and aim to go to that laboratory?”. I think it was partly naivety.Joan H: That''s a lesson for everyone, to go for your dreams, and don''t assume people won''t take notice of you. It is more difficult now, when scientists receive hundreds of e-mail applications from prospective PhD students in their inbox. You would have written a letter with a stamp on it that probably took three weeks to arrive, but it just shows you that you should be audacious. Did you have a different experience to Joan when you arrived? Was there a proper project already lined up for you?Suzanne: I was interviewed by Francis Crick and Sydney Brenner, who were the joint directors of the department. They decided that I would work on the structure of the methionyl-tRNA that puts methionine into internal positions in polypeptides. After they described the project – which involved doing counter-current distribution fractionation of bulk tRNAs, in which I had no experience whatsoever – Sydney in his very characteristic monotone said, “Do you think you''re up to it?”. I sort of gulped to myself and said, “Yes, I think I could do that”. I then went to Brian Clark''s laboratory, who was going to be my PhD supervisor, and started the project. Like always in life, if you learn from people and just go from one day to the next, you actually get there in the end.Joan H: So, persistence was key. Were there many other women at the LMB at the time?Suzanne: I don''t remember any female scientists who had official senior positions. There were certainly some strong female scientists there, but I don''t think they were given the recognition or the status that they actually deserved.Joan S: Later, some were given more recognition, crystallographers in particular, but not so much the molecular biologists.Suzanne: I think, as women, we both pioneered in that department.Joan H: Given the fact that you both agreed to take on projects you had very little previous experience with and that the male supervisors thought you weren''t going to have the mettle to carry it through, once you were there, did you feel that you had to work the whole time? Or did you still manage to have lots of fun and partake in opportunities that Cambridge had to offer at the time?Joan S: We certainly partook in a lot of those things. My husband and I got interested in antique furniture, antique paintings, and used to scour the countryside for little antique shops. We saw lots of England, then a little bit of Scotland and Wales. It was wonderful. A real adventure.Suzanne: I worked really hard most of the time that I was in Cambridge, as the work was very exciting. But I would take holiday periods, camping and youth hostelling all over Europe with a girlfriend from Melbourne and later, travelling with Jerry. We also would go to London for the opera and looking for amazing clothes on Carnaby Street and Chelsea Road (this was the Beatles era, late 60s). Jerry once came back with a purple velvet suit, which was his prized possession for many years. There was lots of fun but also lots of work.Open in a separate windowJoan Steitz, Tom Steitz, Jerry Adams and Suzanne Cory (from left to right) in the Swiss Alps, 1970. Image courtesy of Mark Bretscher. This image in not reproduced under the terms of the Creative Commons Attribution 2.0 Generic license. For permission to reproduce, contact the DMM Editorial office. Joan H: Can you remember the first moment in that part of your career that gave you the most pleasure? Joan S: I worked on a project for about a year, and it turned out that I was doing the wrong fractionation method to get the material that I needed to analyse. Then I had a conversation with Sydney Brenner telling him that I was going to give this one more try with a new method, and then I was going to give up. I remember Sydney saying, “Sometimes, like with a bad marriage, you have to give experiments one last try before you give them up.” Then I tried again, and it worked. This is often the case in science, that you try something new, that''s a little bit different, and it makes all the difference. Then you''re running.Suzanne: The same thing happened to me. I was labouring away on the counter current distribution machines fractionating methionine tRNA, with the goal of sequencing it by the laborious procedure recently published by Robert Holley. However, Fred Sanger, in the department upstairs, had invented a totally new method for sequencing using ³²P-labelled RNA. I desperately wanted to try this, so I managed to persuade my supervisor that we should change techniques. That change was key to my future because the approach was successful. I still remember to this day exactly where I was in Cambridge, walking on a Sunday afternoon, when the last piece of the puzzle dropped into place in my mind, and I had the entire sequence. In that moment, I was extremely joyful, because I knew I had my PhD and that I had succeeded. So that was my eureka moment.Joan H: Obviously, these were extremely productive years, and you''ve mentioned several Nobel Prize winners in your midst. It must have been the most inspiring environment, which I''m sure had a big impact on what you did next. By this stage in your career, were you already feeling ambitious or was it still your scientific curiosity that was driving your path?

“I expected that I would go back to the United States and be a research associate in some man''s lab […]. Then it turned out that people were more impressed than I thought and started offering me junior faculty jobs.”

Joan S: I had gotten a lot of recognition for having sequenced a piece of mRNA, using the same methods that Suzanne used to sequence tRNA. However, I had no expectations, because I had never seen a woman as a science professor, or head of a lab. I expected that I would go back to the United States and be a research associate in some man''s lab, and maybe they''d let me guide a graduate student. Then it turned out that people were more impressed than I thought and started offering me junior faculty jobs.My husband had already secured a junior faculty job in Berkeley before we even went to England, so we went back there after two years. My husband went to the chair of the department in Berkeley and put down letters on his desk of job offers that both of us had received for independent, junior faculty positions from several universities. The Chairman then said to Tom, “But all of our wives are research associates in our labs, and they love it”. This tore at my pride, as there had been a couple of universities that offered us both faculty jobs, and Berkeley was only offering one. So, we didn''t stay at Berkeley, and we came to Yale, which was wonderful.Suzanne: It''s really amazing to think that they gave you up. How foolish they were.Joan H: They''ve lived to regret it a million times over. Suzanne, at that point were you ready to climb this very difficult ladder?Suzanne: Like Joan, I didn''t have any expectations. For me, it was a matter of being able to continue discovering things in science. Jerry had already arranged to start a postdoc in Geneva. So, I applied for a postdoctoral fellowship, and obtained one. We went off together to Geneva to start our married life, and that was the beginning of us doing science together, which we''ve done ever since. I think without Jerry guiding me at that stage in my life, I would have probably drifted out of science. I don''t think I had the scientific confidence to ever think that I would be running a lab. For me, it was just continuing a voyage of discovery; and being lucky to end up in a wonderful scientific partnership and, through that partnership, my confidence grew over the years. Joan H: How many years after your postdoctoral training was it before you looked around your environment and had the confidence to think that you could be a lab or department head or could run an Institute? Joan S: I would say that confidence just grew. Tom and I were part of a departmental overhaul that involved hiring about six new people at Yale. We all stuck together, supported each other and were very collegial even though we worked in different areas. I think the collegial nature of the department in Yale helped me gain confidence. It was very scary at first because I didn''t know if I could write grants or direct people.Suzanne: Cambridge had an incredible influence, certainly over me, and I''m sure over Joan, Tom and Jerry, too. We looked around and saw all these amazing Nobel laureates, but also all these very ambitious, talented postdocs from around the world. I don''t think anyone thought about being the head of a department at that stage. We were simply striving to make discoveries and we gave each other mutual confidence, and stiff competition, too.The other thing that Cambridge gave us, was a new technology. For Joan and me, it was RNA sequencing. Being able to do that technology opened doors all around the world. I now always advise young people to go to the best place in the world to train in your chosen subject and acquire a new technology, because that will open the door to many opportunities in the future.Jerry and I made some excellent discoveries in Geneva, which were published in front-rank journals. Then it was time to move to full independence. I really wanted to go back to Australia but, as Jerry is an American, it was not at all obvious that he should take the big leap of moving to the bottom of the world and starting a lab there. I owe him a tremendous debt because he decided that he would take that risk.Earlier, whilst on our honeymoon, we had visited various labs in Australia. Although WEHI was an institute for immunology, a field we knew little about at that stage, it had the same atmosphere as the LMB in the sense that everyone was striving at the frontiers of science and competing with the rest of the world. We decided this was the only place in Australia that we would work at and that we would attempt to persuade the new director Gus Nossal that he needed molecular biologists. We had an interview with him in Switzerland and he offered us jobs as postdocs. Again, we were probably very naive and audacious but we told him we didn''t want to be postdocs – we wanted to run our own lab. And he agreed and we launched our fledgling lab together in 1971. What drove us was always discovery, rather than career ambitions.Joan H: You''ve both described these amazing sets of circumstances that were challenging but, nevertheless, very satisfying. However, a lot of things have since changed. What do you think are the main remaining barriers to women in science?Joan S: There is an important phenomenon called social identity threat, or stereotype threat, that I think still impedes women in proceeding in their careers. The phenomenon is described by cognitive psychologists as a reaction that all people experience if they feel that they are part of an undervalued minority. And so, by definition, since there are fewer women in science than there are men, women are being subjected to stereotype threat. Cognitive psychologists have studied the physiological manifestations of this, including increased heart rate and perspiration but, psychologically, they''ve also documented that cognitive learning and memory are impaired when one has these feelings.I first learned about this in 2007 and I looked back and realized why, for 30 years, when I''d been on committees as the only woman amongst ten men, I wouldn''t dare say anything – because I was frightened stiff. Men undergo this response, too, if they''re put into the situation of being undervalued. If you understand why you''re reacting the way you''re reacting and know that this is a normal human response, I think it helps you to overcome your own feelings of insecurity and allows you to go ahead. I always tell young women who I''m rooting for in science about this, because I want them to know that they will very likely end up feeling this way, and it''s a normal human response.

“One thing I sometimes get frustrated about is that we often need men to change things […] but what we really need are women in those high-level positions, so that they can be the champions of change.”

Joan H: There are other terms describing other relevant phenomena, such as unconscious bias, imposter syndrome and champions of change. One thing I really relate to is imposter syndrome. I''ve listened to webinars on this topic and they all reach a similar conclusion that we all feel the same. On the one hand, at the end of the webinar, you do feel somewhat elated to know that it''s not just you, and that it''s normal. But, on the other hand, it doesn''t really change things. It''s a recognition of what we feel, and we all get some help from that, but you really need opportunities to change things at a higher level. One thing I sometimes get frustrated about is that we often need men to change things, leading to this concept of male champions of change. I admire those men; but what we really need are women in those high-level positions, so that they can be the champions of change. Not having 50% of university departments and medical research institutes run by women still limits our full potential.Joan S: I certainly agree with you, Joan. It''s very important to have realistic role models. Suzanne being head of the WEHI for all those years has engendered all sorts of admiration.Joan H: During that period, Suzanne not only did fantastic science but our Institute doubled in size.It''s transformative when you have women making up 50% of people around the table. It''s no help just having a token female because that poor person''s not going to be able to change everything on her own. In American scientific institutions, are there any firm quotas for female scientists and other people that are underrepresented in science?Joan S: In recent years there has been a push in that direction. Sometimes it''s successful and sometimes it''s not. It is very different now compared to when there was no consciousness that this was unfair or that things could be better if we had real representation.Suzanne: I agree with both of you in everything that''s been said. While reflecting at this moment, what it says to me is that what''s really needed is societal change, and that we need to give courage to girls from the very earliest age. It should come naturally, they shouldn''t feel inferior, and others should not look at them as inferior. They should expect to have careers as well as families, be able to manage both and have somebody alongside them who helps them manage both.I think that affirmative action for women in science is necessary because the pace of change has been so slow. However, I also think quotas can be detrimental to the cause of women, in the sense that it''s then possible for people to say you only made it because there was a quota – which is very destructive. If I look back on our careers in science, it is clear that things have changed tremendously. Today there are more opportunities for women because many universities and institutes are bending over backwards to equalise things. The downside of this is that talented men may miss out on positions because of this policy and the pendulum could swing back.Joan H: The evidence shows that when more women are involved in things, those things go better. For instance, boards that have more women on them are more productive. Obviously, what you alluded to is there are lots of fantastic male scientists as well. The real issue here is there''s not enough funding to go round to support all the great men and women. But there are clearly enough good women around to be represented at the 50% level, without disproportionately disadvantaging male scientists.Joan S: Men and women are now operating on a more even playing field, which doesn''t mean that the men are missing out. They''re just in a more-competitive situation – as they should be. Joan H: Suzanne previously covered the specific advice she would give to young female researchers. Joan, do you have any other suggestions? Joan S: I encourage them to try lots of different things in science, and when they find something that really grabs them, then go for it and be persistent. We all know that science is very up and down. But if you keep pushing when you''re in a trough, it will always go back up again and you will succeed. That''s harder for a young person, who hasn''t experienced these troughs, to understand.Joan H: Yes, and the period when women scientists start having children is the hardest part. It''s still a choice that some women make, to take some years off and come back with a less ambitious plan for their career. Obviously, things like maternity leave payments and so on are improving but there''s no question that, in most circumstances, the research will slow down during that period.Suzanne: What I say to young women at that stage of their careers is that you have to be very focused, you must spend the time that you do have in a very focused manner, so that you can be the most productive you can be. But you have to be supported at home by your partner. If you''re both scientists it''s easier because you can appreciate why the other person is rushing into the lab late at night, for example, but for most people, that''s not true. So, what is really important is equal sharing of responsibilities from both partners when young families are around. And I think employers need to give both of those partners a longer time to achieve the kind of papers that they need to progress in their careers. That''s a period when it is much harder to be productive, and we need to continue to support people during that difficult phase of their careers because we''ve invested so much in them. They have so much to offer to science and to society, so to let them slip out at that stage is a great waste.Joan H: Let''s change tack a little bit and think about some of the broader challenges in science. What do you think the COVID-19 pandemic has taught us about the importance of clear scientific communication and real engagement with the community?Joan S: Whenever I talk to people about this, I very clearly make the point that it was decades of fundamental research that led to the development of the COVID-19 vaccine. If it hadn''t been for those fundamental discoveries in how cells and mRNA work, it would never have only taken 63 days from sequencing the virus to phase one clinical trials at Moderna. I try to point out to people that all the different discoveries coming in from different angles made that possible. I personally find it absolutely remarkable that all that knowledge could be harnessed, so very quickly. I''ve been doing fundamental research my entire life and I never expected to see it materialise in the way it has. It''s a wonderful reward. Joan H: Do you think this has resulted in the community appreciating scientists more? Joan S: I don''t think we''re far enough downstream to know that. In the US, there has been a congressional vote to abandon our maintenance of vigilance and preparedness for future pandemics – which seems ridiculous. Now we have all these procedures set up, all we have to do is maintain them for the next one. Whereas, if we just let go of these procedures, we''ll have to start over again for future pandemics. I guess we''re not good enough at communicating some of these things at this point.Joan H: Millions of people died from the virus and yet, if we hadn''t had the vaccines, the scale would have been even more horrific. If we were able to convey this information effectively to the public, then, hopefully, people would recognise that – as well as spending a fixed percentage of the gross domestic product on defence, for example – we should spend at least the same amount on science. Not only for pandemics but for tackling climate change and other pressing issues. I like to think this is an auspicious time but I don''t know whether we are really taking advantage of it.Suzanne: The pandemic has brought science and scientists to the forefront, and there has been a period of great respect for scientists having developed the vaccine. It''s an absolute miracle that it was done so fast and effectively. We''re very fortunate but, as Joan said, that was not luck. It was through investment in basic science for decades. We have to keep conveying this message, to our politicians in particular, so that they will keep supporting all kinds of scientists, because we never know what''s around the corner.Joan H: Certainly, people like Anthony Fauci in the US and Catherine Bennett in Melbourne, spoke eloquently and had a real talent for communicating things clearly and in a nutshell. That''s not something we''re all good at and it''s not something that is easy to train into people either. I think we all need to try to capture the attention of the community at large, by speaking plainly. I don''t think people understand that scientists are underfunded and could do so much more if funding was more generous.

“All I can say to young people is, if you really love science and have a passion for it, keep trying – because you will succeed if you put your whole heart and soul into this career path.”

Suzanne: I think the general public has no appreciation of how tenuous the life of a scientist can be, and how we are losing so many great minds entering the field because young people just finishing their PhDs look with dismay at how hard it is to support a career in science and get enough funding. There''s a tremendous waste of talent. All I can say to young people is, if you really love science and have a passion for it, keep trying – because you will succeed if you put your whole heart and soul into this career path.Joan H: This has been an absolutely fantastic discussion and it''s such a delight to talk to women who, after all these years, are still as passionate as ever and are pursuing their scientific subjects with the same vigour as they have all along.Suzanne: It''s been wonderful to talk with you, Joan, and I hope that we see each other soon, no matter what continent. And thank you, Joan Heath for getting us together and giving us this opportunity.     

Timeline: AIDS pathogenesis: what have two decades of HIV research taught us?

22 years ago, the first cases of an acquired immunodeficiency syndrome afflicting young, homosexual American men were reported, heralding what we now know to be the beginning of the HIV epidemic. Since then, billions of US dollars have been invested in HIV research in the hope of gaining a better understanding of this infection and how to prevent and treat it. What are the landmarks in HIV research over the past two decades, and what questions still remain to be answered? What has the intense study of HIV infection taught us about other virus infections and how our immune system responds to them?     

Photosynthetic response to fluctuating environments and photoprotective strategies under abiotic stress

Plants in natural environments must cope with diverse, highly dynamic, and unpredictable conditions. They have mechanisms to enhance the capture of light energy when light intensity is low, but they can also slow down photosynthetic electron transport to prevent the production of reactive oxygen species and consequent damage to the photosynthetic machinery under excess light. Plants need a highly responsive regulatory system to balance the photosynthetic light reactions with downstream metabolism. Various mechanisms of regulation of photosynthetic electron transport under stress have been proposed, however the data have been obtained mainly under environmentally stable and controlled conditions. Thus, our understanding of dynamic modulation of photosynthesis under dramatically fluctuating natural environments remains limited. In this review, first I describe the magnitude of environmental fluctuations under natural conditions. Next, I examine the effects of fluctuations in light intensity, CO₂ concentration, leaf temperature, and relative humidity on dynamic photosynthesis. Finally, I summarize photoprotective strategies that allow plants to maintain the photosynthesis under stressful fluctuating environments. The present work clearly showed that fluctuation in various environmental factors resulted in reductions in photosynthetic rate in a stepwise manner at every environmental fluctuation, leading to the conclusion that fluctuating environments would have a large impact on photosynthesis.     

Upper limits of photosynthetic productivity and problems of scaling

Some 1,370 W m^?2 of light energy reaches the outer atmosphere of earth and on average only 240 W m^?2 reaches the earth’s surface. Only a fraction of this is used to fix CO₂ through photosynthesis, and efficiencies ranging from 0.1?8% for total irradiance have been reported. The theoretical maximum quantum efficiency of carbon fixation is 0.125 mol C (mol quanta)^?1 which relates to a maximum productivity of about 12 g C m^?2 day^?1 or 29.8 g(dw) m^?2 day^?1. This could increase to a maximum of 200 g(dw) m^?2 day^?1 in intermittent light of high frequencies, which is on average eight times higher than the average measured under field conditions where rates approaching 25 g(dw) m^?2 day^?1 are considered high. Several possibilities exist for achieving higher yields and photosynthetic efficiencies, such as limiting the antennae sizes and pulsing light at frequencies equivalent to electron turnover in the electron transport chains of photosynthesis. Scaling from laboratory experimental conditions to large commercial photobioreactors is a major stumbling block and may be the single most important factor responsible for the overall low reported areal production rates.     

The effect of light availability on the photosynthetic activity and productivity of outdoor cultures of Arthrospira platensis (Spirulina)

The basic requirement for establishing economically viable large-scale production of algal biomass, be it for food, feed, high-value product, or energy, is the ability to produce the biomass at a low price. To achieve this goal, an efficient production protocol is needed that ensures that the potential productivity is obtained at any given time. When productivity is defined by the ability to utilize the available solar radiation that drives photosynthesis, the production protocol must be optimized to meet this requirement. In the current study, we demonstrate that by modifying the light available to Arthrospira platensis cells cultured outdoors by a variety of options like modifying the standing biomass concentration, changing the mixing rate, or shading can change the potential photosynthetic activity and apparent activity. By optimizing the light available to algae cells under outdoor conditions, productivity can be increased by approximately 50 %, from 15.6 g m^?2 day^?1 in a culture that suffers from overexposure to light to 22.4 g m^?2 day^?1 in a culture in which light downregulation is minimized. Therefore, by using a variety of methodologies to estimate photosynthetic activity, we demonstrate that overexposing the cells to light may result in downregulation of the photosynthetic activity leading to photoinhibition and lower biomass productivity.     

Work life balance?

There is no perfect recipe to balance work and life in academic research. Everyone has to find their own optimal balance to derive fulfilment from life and work. Subject Categories: S&S: Careers & Training

A few years ago, a colleague came into my office, looking a little irate, and said, “I just interviewed a prospective student, and the first question was, ‘how is work‐life balance here?’”. Said colleague then explained how this question was one of his triggers. Actually, this sentiment isn''t unusual among many PIs. And, yet, asking about one''s expected workload is a fair question. While some applicants are actually coached to ask it at interviews, I think that many younger scientists have genuine concerns about whether or not they will have enough time away from the bench in order to have a life outside of work.In a nutshell, I believe there is no one‐size‐fits‐all definition of work–life balance (WLB). I also think WLB takes different forms depending on one''s career stage. As a new graduate student, I didn''t exactly burn the midnight oil; it took me a couple of years to get my bench groove on, but once I did, I worked a lot and hard. I also worked on weekends and holidays, because I wanted answers to the questions I had, whether it was the outcome of a bacterial transformation or the result from a big animal experiment. As a post‐doc, I worked similarly hard although I may have actually spent fewer hours at the bench because I just got more efficient and because I read a lot at home and on the six train. But I also knew that I had to do as much as I could to get a job in NYC where my husband was already a faculty member. The pressure was high, and the stress was intense. If you ask people who knew me at the time, they can confirm I was also about 30 pounds lighter than I am now (for what it''s worth, I was far from emaciated!).As an assistant professor, I still worked a lot at the bench in addition to training students and writing grant applications (it took me three‐plus years and many tears to get my first grant). As science started to progress, work got even busier, but in a good way. By no means did I necessarily work harder than those around me—in fact, I know I could have worked even more. And I’m not going to lie, there can be a lot of guilt associated with not working as much as your neighbor.My example is only one of millions, and there is no general manual on how to handle WLB. Everyone has their own optimal balance they have to figure out. People with children or other dependents are particularly challenged; as someone without kids, I cannot even fathom how tough it must be. Even with some institutions providing child care or for those lucky enough to have family take care of children, juggling home life with “lab life” can create exceptional levels of stress. What I have observed over the years is that trainees and colleagues with children become ridiculously efficient; they are truly remarkable. One of my most accomplished trainees had two children, while she was a post‐doc and she is a force to be reckoned with—although no longer in my laboratory, she still is a tour de force at work, no less with child number three just delivered! I think recruiters should view candidates with families as well—if not better—equipped to multi‐task and get the job done.There are so many paths one can take in life, and there is no single, “correct” choice. If I had to define WLB, I would say it is whatever one needs to do in order to get the work done to one''s satisfaction. For some people, putting in long days and nights might be what is needed. Does someone who puts in more hours necessarily do better than one who doesn''t, or does a childless scientist produce more results than one with kids? Absolutely not. People also have different goals in life: Some are literally “wedded” to their work, while others put much more emphasis on spending time with their families and see their children grow up. Importantly, these goals are not set in stone and can fluctuate throughout one''s life. Someone recently said to me that there can be periods of intense vertical growth where “balance” is not called for, and other times in life where it is important and needed. I believe this sentiment eloquently sums up most of our lives.Now that I''m a graying, privileged professor, I have started to prioritize other areas of life, in particular, my health. I go running regularly (well, maybe jog very slowly), which takes a lot of time but it is important for me to stay healthy. Pre‐pandemic, I made plans to visit more people in person as life is too short not to see family and friends. In many ways, having acquired the skills to work more efficiently after many years in the laboratory and office, along with giving myself more time for my health, has freed up my mind to think of science differently, perhaps more creatively. It seems no matter how much I think I’m tipping the balance toward life, work still creeps in, and that’s perfectly OK. At the end of the day, my work is my life, gladly, so I no longer worry about how much I work, nor do I worry about how much time I spend away from it. If you, too, accomplish your goals and derive fulfillment from your work and your life, neither should you.     

Photosynthetic efficiency and oxygen evolution of Chlamydomonas reinhardtii under continuous and flashing light

As a result of mixing and light attenuation in a photobioreactor (PBR), microalgae experience light/dark (L/D) cycles that can enhance PBR efficiency. One parameter which characterizes L/D cycles is the duty cycle; it determines the time fraction algae spend in the light. The objective of this study was to determine the influence of different duty cycles on oxygen yield on absorbed light energy and photosynthetic oxygen evolution. Net oxygen evolution of Chlamydomonas reinhardtii was measured for four duty cycles (0.05, 0.1, 0.2, and 0.5) in a biological oxygen monitor (BOM). Oversaturating light flashes were applied in a square-wave fashion with four flash frequencies (5, 10, 50, and 100 Hz). Algae were precultivated in a turbidostat and acclimated to a low photon flux density (PFD). A photosynthesis–irradiance (PI) curve was measured under continuous illumination and used to calculate the net oxygen yield, which was maximal between a PFD of 100 and 200 μmol m^?2?s^?1. Net oxygen yield under flashing light was duty cycle-dependent: the highest yield was observed at a duty cycle of 0.1 (i.e., time-averaged PFD of 115 μmol m^?2?s^?1). At lower duty cycles, maintenance respiration reduced net oxygen yield. At higher duty cycles, photon absorption rate exceeded the maximal photon utilization rate, and, as a result, surplus light energy was dissipated which led to a reduction in net oxygen yield. This behavior was identical with the observation under continuous light. Based on these data, the optimal balance between oxygen yield and production rate can be determined to maximize PBR productivity.     

A Comparison of the Energy Yield at the End User for M. x giganteus Using Two Different Harvesting and Transport Systems

A comparison between two different harvest systems for Miscanthus x giganteus crop (direct cut/chip and mow/bale) in terms of the net energy delivered to an end user, and the various energy costs and energy yields associated with each system was conducted. Only minor differences in terms of energy consumption were observed between the two harvest systems when all phases of the harvesting chain had been taken into account. Chip harvesting consumed 0.11 GJ?t^?1 compared with 0.13 GJ?t^?1 for bale harvesting. Chip transportation was considerably more expensive than bale transportation for a set distance of 50 km (0.18 and 0.11 GJ?t^?1 for chip and bale, respectively). Despite this, higher overall net energy yield was achieved by direct cutting and chipping the material. This was due to the higher proportion of harvestable energy lost in the field as a result of the use of a mowing/baling system. The overall net energy delivered in terms of harvestable material by the direct cut and chip system was 12.45 GJ?t^–1 compared with 11.78 GJ?t^?1 by the mow and bale system, making direct cut the more efficient system even up to a transport distance of 400 km. A sensitivity analysis indicated that the choice of transport system becomes more important for energy efficiency as transport distance increases.