Photosynthesis, photorespiration and nitrogen metabolism

Abstract. The ATP and reduced ferredoxin generated in photosynthetic reactions in the chloroplast are utilized for a large number of reactions other than CO₂-fixation. Quantitatively the most important reaction is the reassimilation of ammonia liberated during photorespiration in C₃ plants via the glutamate synthase cycle. Chloroplasts are also able to reduce nitrite to ammonia, sulphate to sulphide, and synthesize a number of amino acids. The amino acids essential for human nutrition are all synthesized in the chloroplast and evidence is presented to suggest that they may be the sole site of such biosynthetic reactions.     

Photosynthesis

Book Review

PhotosynthesisA. Amesz (Ed)., Amsterdam: Elsevier 1987. 355 pages. £57.27. ISBN 0-444-80864-7     

Photosynthesis,inorganic plant nutrition,solutions, and problems

A brief account is given of the research that D.I. Arnon did before he ventured into the field of photosynthesis, viz. his work on inorganic plant nutrition in the laboratory of D.R. Hoagland. The connection between the two areas is indicated. In his work on plant nutrition Dr Arnon emphasized the role of specific nutrients and, with P.R. Stout, formulated a definition of essentiality that is used to this day. It is now necessary, however, to take into account elements not meeting their criteria of essentiality, as shown by a consideration of the element silicon.     

Photosynthesis, growth, and the role of chloride

Previous studies with isolated chloroplasts have indicated that Cl⁻ is an essential cofactor for photosynthesis. Considerable support for the postulated Cl⁻ requirement in photosynthesis came from the observation that Cl⁻ is essential for growth. Data are presented which show that a 60% reduction in growth which occurred in Cl⁻ -deficient sugar beet (Beta vulgaris L.) was not due to an effect of Cl⁻ on the rate of photosynthesis in vivo (net CO₂ uptake per unit area of attached leaves). The principal effect of Cl⁻ deficiency was to lower cell multiplication rates in leaves, thus slowing down their growth and ultimately decreasing their area. The absence of an effect of Cl⁻ on photosynthesis in vivo was unlikely to have been due to Cl⁻ retention by the chloroplasts because their Cl⁻ concentration (measured after nonaqueous isolation) decreased progressively with decrease in leaf Cl⁻.     

Effects of Light, Carbon Dioxide, and Temperature on Photosynthesis, Oxygen Inhibition of Photosynthesis, and Transpiration in Solanum tuberosum

Individual leaves of potato (Solanum tuberosum L. W729R), a C₃ plant, were subjected to various irradiances (400-700 nm), CO₂ levels, and temperatures in a controlled-environment chamber. As irradiance increased, stomatal and mesophyll resistance exerted a strong and some-what paralleled regulation of photosynthesis as both showed a similar decrease reaching a minimum at about 85 neinsteins·cm⁻²·sec⁻¹ (about ½ of full sunlight). Also, there was a proportional hyperbolic increase in transpiration and photosynthesis with increasing irradiance up to 85 neinsteins·cm⁻²·sec⁻¹. These results contrast with many C₃ plants that have a near full opening of stomata at much less light than is required for saturation of photosynthesis.     

Photosynthesis of ATP-electrons,proton pumps,rotors, and poise

Light-driven electron transport is coupled to ATP synthesis in chloroplasts. While the nature of the coupling and the structures of key components are now known, there has long been disagreement over pathways of electron transport. Recent results now put an old idea back on the agenda-cyclic electron transport around photosystem I.     

Improving Photosynthesis

Photosynthesis is the basis of plant growth, and improving photosynthesis can contribute toward greater food security in the coming decades as world population increases. Multiple targets have been identified that could be manipulated to increase crop photosynthesis. The most important target is Rubisco because it catalyses both carboxylation and oxygenation reactions and the majority of responses of photosynthesis to light, CO₂, and temperature are reflected in its kinetic properties. Oxygenase activity can be reduced either by concentrating CO₂ around Rubisco or by modifying the kinetic properties of Rubisco. The C₄ photosynthetic pathway is a CO₂-concentrating mechanism that generally enables C₄ plants to achieve greater efficiency in their use of light, nitrogen, and water than C₃ plants. To capitalize on these advantages, attempts have been made to engineer the C₄ pathway into C₃ rice (Oryza sativa). A simpler approach is to transfer bicarbonate transporters from cyanobacteria into chloroplasts and prevent CO₂ leakage. Recent technological breakthroughs now allow higher plant Rubisco to be engineered and assembled successfully in planta. Novel amino acid sequences can be introduced that have been impossible to reach via normal evolution, potentially enlarging the range of kinetic properties and breaking free from the constraints associated with covariation that have been observed between certain kinetic parameters. Capturing the promise of improved photosynthesis in greater yield potential will require continued efforts to improve carbon allocation within the plant as well as to maintain grain quality and resistance to disease and lodging.Photosynthesis is the process plants use to capture energy from sunlight and convert it into biochemical energy, which is subsequently used to support nearly all life on Earth. Plant growth depends on photosynthesis, but it is simplistic to think that growth rate directly reflects photosynthetic rate. Continued growth requires the acquisition of water and nutrients in addition to light and CO₂ and, in many cases, involves competition with neighboring plants. Biomass must be invested by the plant to acquire these resources, and respiration is necessary to maintain all the living cells in a plant. Photosynthetic rate is typically measured by enclosing part of a leaf in a chamber, but to understand growth, one needs to consider the daily integral of photosynthetic uptake by the whole plant or community and how it is allocated. Almost inevitably, changing photosynthesis in some way requires more resources. Consequently, in order to improve photosynthesis, one needs to consider the tradeoffs elsewhere in the system. The title, “Improving Photosynthesis,” could be interpreted in many ways. For this review, I am restricting the scope to focus on crop species growing under favorable conditions.To support the forecast growth in human population, large increases in crop yields will be required (Reynolds et al., 2011; Ziska et al., 2012). Dramatic increases in yield were achieved by the Green Revolution through the introduction of dwarfing genes into the most important C₃ cereal crops rice (Oryza sativa) and wheat (Triticum aestivum). This allowed greater use of fertilizer, particularly nitrogen, without the risk of lodging, where the canopy collapses under the weight of the grain, causing significant yield losses (Stapper and Fischer, 1990). It also meant that biomass allocation within the plant could be altered to increase grain mass at the expense of stem mass now that the plants were shorter. Retrospective comparisons of cultivars released over time, but grown concurrently under favorable conditions with weed, pest, and disease control and physical support to prevent lodging, reveal that while modern cultivars yield more grain, they have similar total aboveground biomass (Austin et al., 1980, 1989).It is interesting to revisit the review by Gifford and Evans (1981): “over the course of evolution from the wild plant to modern cultivar, carbon partitioning was improved. Thus, as remaining scope for further improvement in carbon allocation must be small, it would be better to aim at increasing photosynthetic and growth rates. Alternatively, as partitioning is where flexibility has been manipulated in the past, it is better to aim for further increases in harvest index.” Just over 30 years have passed since this was published, and yield gains made by plant breeders have continued to come largely from increasing carbon allocation into grain (Fischer and Edmeades, 2010) and selecting for increased early vigor (Richards et al., 2010). By contrast, selection based on improving photosynthesis has yet to be achieved. Plants need leaves and roots to capture light, water, and nutrients for growth and stems to form the leaf canopy and support the flowers and grain, so further increases in harvest index may lead to a decrease in yield. Therefore, in order to increase yield potential further, it is necessary to increase total biomass. If light interception through the growing season is already fully exploited, then increasing biomass requires that photosynthesis be increased. It is the realization that further significant increases in yield potential will not be possible by continuing the current strategy that has turned attention toward improving photosynthesis. Recent technological developments now provide us with the means to engineer changes to photosynthesis that would not have been possible previously.     

Photosynthesis online

Online access to the Internet and the World Wide Web have become important for public awareness and for educating the world’s population, including its political leaders, students, researchers, teachers, and ordinary citizens seeking information. Relevant information on photosynthesis-related Web sites and other online locations is grouped into several categories: (1) group sites, (2) sites by subject, (3) individual researcher’s sites, (4) sites for educators and students, and (5) other useful sites.     

Photosynthesis for Food, Fuel and the Future

<正>Photosynthesis is a process that converts solar energy to chemical energy in many different organisms,ranging from plants to bacteria.Photosynthesis provides all the food we eat and all the fossil fuel we use.Photosynthesis has long been studied in order to understand its underlying mechanisms a     

Microclimate, Canopy Structure and Photosynthesis in Canopies of Three Contrasting Temperate Forage Grasses: III. Canopy Photosynthesis, Individual Leaf Photosynthesis and the Distribution of Current Assimilate

The rates of canopy and individual leaf photosynthesis and ¹⁴Cdistribution for three temperate forage grasses Lolium perennecv. S24, L. perenne cv. Reveille and Festuc'a arundinacea cv.SI70 were determined in the field during a summer growth period.Canopy photosynthesis declined as the growth period progressed,reflecting a decline in the photosynthetic capacity of successiveyoungest fully expanded leaves. The decline in the maximum photosyntheticcapacity of the canopies was correlated with a decline in theirquantum efficiencies at low irradiance. Changes in canopy structureresulted in changes in canopy net photosynthesis and dark respiration.No clear relationships between changes in the environment andchanges in canopy net photosynthesis and dark respiration wereestablished. The relative distributions of ¹⁴C in the shootsof the varieties gave a good indication of the amount of drymatter per ground area in the varieties.     

Photosynthesis, photorespiration, and light signalling in defence responses

Visible light is the basic energetic driver of plant biomass production through photosynthesis. The constantly fluctuating availability of light and other environmental factors means that the photosynthetic apparatus must be able to operate in a dynamic fashion appropriate to the prevailing conditions. Dynamic regulation is achieved through an array of homeostatic control mechanisms that both respond to and influence cellular energy and reductant status. In addition, light availability and quality are continuously monitored by plants through photoreceptors. Outside the laboratory growth room, it is within the context of complex changes in energy and signalling status that plants must regulate pathways to deal with biotic challenges, and this can be influenced by changes in the highly energetic photosynthetic pathways and in the turnover of the photosynthetic machinery. Because of this, defence responses are neither simple nor easily predictable, but rather conditioned by the nutritional and signalling status of the plant cell. This review discusses recent data and emerging concepts of how recognized defence pathways interact with and are influenced by light-dependent processes. Particular emphasis is placed on the potential roles of the chloroplast, photorespiration, and photoreceptor-associated pathways in regulating the outcome of interactions between plants and pathogenic organisms.     

Microclimate, Photosynthesis and Growth of Lucerne (Medicago sativa L.). I. Microclimate and Photosynthesis

Measurements of microclimate and photosynthesis of lucerne var.Europe were made in the field during the spring of 1976. Themaximum rate of canopy gross photosynthesis (14.3 g CO₂ m^–2h^–1, I = ) was 2.5 times greater than that of S 24 perennialryegrass at the same LAI. This difference was due to differencesin individual leaf photosynthesis. The photosynthetic rate ofthe youngest fully expanded leaf of lucerne remained constantthroughout the experimental period at 3.6 g CO₂ m^–2 h^–1(300 W m^–2). Measurements of soil water potential profiles indicated thatlucerne extracted water from the soil to a depth of at least800 mm, with a region of maximum uptake between 400 and 600mm. This capability, with a moderate mean leaf resistance of460 s m^–1, conferred a high assimilation efficiency onlucerne, with a mean water use efficiency of 34 g H₂O lost pergram of carbohydrate assimilated, compared with 200 g H₂O pergram of carbohydrate for S 24. Medicago sativa L, lucerne, photosynthesis, assimilation efficiency     

Announcement – Advances in Photosynthesis and Respiration,Volume 11, ‘Regulation of Photosynthesis’ , edited by Eva-Mari Aro and Bertil Andersson

Photosynthesis Research -     

Ke, B. Photosynthesis: photobiochemistry and photobiophysics

This volume is the tenth in the major series on photosynthesis,Advances in photosynthesis, and departs from the usually multi-authorvolumes, being by a single author. Bacon Ke has produced a valuableaddition to the review literature covering the reactions thatoccur in the process between 10^–12 and 10^–13 seconds.These fundamental processes are basically the transfer of theenergy of photons to the pigments of the biological system,producing