Control of magnesium–protoporphyrin chelatase activity in Rhodopseudomonas spheroides. Role of light, oxygen, and electron and energy transfer

1. Magnesium-protoporphyrin chelatase activity, previously shown in whole cells of Rhodopseudomonas spheroides, could not be demonstrated in cell-free extracts prepared in different ways, although spheroplasts retained moderate activity. Slight activity was detected also in whole cells of Rhodospirillum rubrum. 2. The effects on the activity of the enzyme of inhibitors of electron and energy transfer were studied in whole cells of Rps. spheroides. Amytal, rotenone, azide and cyanide inhibited at low pO(2) in the dark but not under anaerobic conditions in the light. Antimycin A and 2-heptyl-4-hydroxyquinoline N-oxide, as well as uncouplers and oligomycin, inhibited under all environmental conditions. 3. The effects on magnesium chelatase activity of intermediates of the tricarboxylic acid cycle, of thenoyltrifluoroacetone, of a number of artificial electron donors or acceptors, of various quinones and of the oxidation-reduction indicator dyes Benzyl Viologen and Methyl Viologen are described. 4. It was concluded that electron transport between a b-type and a c-type cytochrome as well as associated energy conservation and transformation reactions were essential for activity. There was also a specific requirement for ATP. 5. Exogenous protoporphyrin and magnesium protoporphyrin monomethyl ester were incorporated into bacteriochlorophyll or late precursors by whole cells. 6. Evidence is presented that the insertion of magnesium was the only step inhibited by oxygen in the biosynthetic pathway between protoporphyrin and bacteriochlorophyll.     

Excitation energy transfer between β-carotene and chlorophyll-a in various systems

The excitation energy transfer from -carotene to chlorophyll-a in several seminatural systems such as liposomes, lipid layers and PSI complex has been studied at room and liquid nitrogen temperature. Only in a case of PSI complex an efficient energy transfer (about 30%) from -carotene to chlorophyll-a has been observed. The results of energy transfer were discussed on the ground of Dexter's mechanism by taking into account the recently discovered energy level (¹Ag) of -carotene.Abbreviations chl-a chlorophyll-a - -car -carotene - R_DA mean donor-acceptor distance - PSI photosystem I - _exe excitation wavelength - _e emission wavelength - d optical pathlength     

Correlating calcium binding, Förster resonance energy transfer, and conformational change in the biosensor TN-XXL

Genetically encoded calcium indicators have become instrumental in imaging signaling in complex tissues and neuronal circuits in vivo. Despite their importance, structure-function relationships of these sensors often remain largely uncharacterized due to their artificial and multimodular composition. Here, we describe a combination of protein engineering and kinetic, spectroscopic, and biophysical analysis of the Förster resonance energy transfer (FRET)-based calcium biosensor TN-XXL. Using fluorescence spectroscopy of engineered tyrosines, we show that two of the four calcium binding EF-hands dominate the FRET output of TN-XXL and that local conformational changes of these hands match the kinetics of FRET change. Using small-angle x-ray scattering and NMR spectroscopy, we show that TN-XXL changes from a flexible elongated to a rigid globular shape upon binding calcium, thus resulting in FRET signal output. Furthermore, we compare calcium titrations using fluorescence lifetime spectroscopy with the ratiometric approach and investigate potential non-FRET effects that may affect the fluorophores. Thus, our data characterize the biophysics of TN-XXL in detail and may form a basis for further rational engineering of FRET-based biosensors.     

Interspecific difference in the photosynthesis–nitrogen relationship: patterns,physiological causes,and ecological importance

The photosynthesis–nitrogen relationship is significantly different among species. Photosynthetic capacity per unit leaf nitrogen, termed as photosynthetic nitrogen-use efficiency (PNUE), has been considered an important leaf trait to characterise species in relation to their leaf economics, physiology, and strategy. In this review, I discuss (1) relations between PNUE and species ecology, (2) physiological causes and (3) ecological implications of the interspecific difference in PNUE. Species with a high PNUE tend to have high growth rates and occur in disturbed or high productivity habitats, while those with a low PNUE occur in stressful or low productivity habitats. PNUE is an important leaf trait that correlates with other leaf traits, such as leaf mass per area (LMA) and leaf life span, irrespective of life form, phylogeny, and biomes. Various factors are involved in the interspecific difference. In particular, nitrogen allocation within leaves and the mesophyll conductance for CO₂ diffusion are important. To produce tough leaves, plants need to allocate more biomass and nitrogen to make thick cell walls, leading to a reduction in the mesophyll conductance and in nitrogen allocation to the photosynthetic apparatus. Allocation of biomass and nitrogen to cell walls may cause the negative relationship between PNUE and LMA. Since plants cannot maximise both PNUE and leaf toughness, there is a trade-off between photosynthesis and persistence, which enables the existence of species with various leaf characteristics on the earth.     

Natural photosystems from an engineer’s perspective: length,time, and energy scales of charge and energy transfer

The vast structural and functional information database of photosynthetic enzymes includes, in addition to detailed kinetic records from decades of research on physical processes and chemical reaction-pathways, a variety of high and medium resolution crystal structures of key photosynthetic enzymes. Here, it is examined from an engineer’s point of view with the long-term goal of reproducing the key features of natural photosystems in novel biological and non-biological solar-energy conversion systems. This survey reveals that the basic physics of the transfer processes, namely, the time constraints imposed by the rates of incoming photon flux and the various decay processes allow for a large degree of tolerance in the engineering parameters. Furthermore, the requirements to guarantee energy and electron transfer rates that yield high efficiency in natural photosystems are largely met by control of distance between chromophores and redox cofactors. This underlines a critical challenge for projected de novo designed constructions, that is, the control of spatial organization of cofactor molecules within dense array of different cofactors, some well within 1 nm from each other.     

Long-term trends,seasonal abundance and energy consumption of waterbirds at Rietvlei,Western Cape,South Africa, 1950–1997

Waterbird counts at Rietvlei, a freshwater wetland in the Western Cape, were analysed for four periods: 1950–56, 1961–67, 1980–85 and 1992–97. Ninety-eight species of waterbirds were recorded during these counts. Palaearctic migrants predominated during summer, with Curlew Sandpipers, Calidris ferruginea, being the mast abundant species in all years, except in the 1960s and 1950s when Red-knobbed Coots, Fulica cristata, and Ruffs, Philomachus pugnax, outnumbered them respectively. Red-knobbed Coots and Yellow-billed Ducks, Anas undulata, were the most numerous species during winter in all years. The numbers of waterbirds at Rietvlei have shown a progressive increase since the 1950s, reaching over 8300 birds in the mid-summer of 1997. The increase in abundance of several species is attributed to changes in the water regime and habitat availability at the wetland. In terms of waterbird abundance, Rietvlei is the most important temporary vlei in the Western Cape and it ranks 16th in terms of waterbird abundance compared with all South African coastal and inland wetlands for which counts are available. In the light of Rietvlei being proclaimed a nature reserve, a conservation management plan for the area is discussed.     

A simple "proximity" correction for Förster resonance energy transfer efficiency determination in membranes using lifetime measurements

Accurate measurements of oligomerization in membranes by Förster resonance energy transfer (FRET) are always compromised by a substantial contribution from random chance colocalization of donors and acceptors. Recently, Li and coworkers demonstrated the use of computer simulation in estimating the contribution of this “proximity” component to correct the FRET efficiency and estimate the free energy of dimer formation of the G380R mutants of fibroblast growth factor receptor 3 (FGFR3) transmembrane domain immersed into lipid bilayer. Because tight dimerization will result in complete energy transfer from donor to acceptor, we have used the same experimental system of fluorescein- and rhodamine-labeled G380R mutants of FGFR3 for the experimental assessment of the proximity FRET corrections using fluorescence lifetime measurements. The experimental proximity FRET correction, based on time-resolved fluorescence measurements, is expected to have general advantages over theoretical correction, especially in the case of nonrandomly distributed monomers.     

Exogenous 7,8-dihydro-8α-20-hydroxyecdysone application improves antioxidative enzyme system,photosynthesis, and yield in rice under high-temperature condition

7,8-Dihydro-8α-20-hydroxyecdysone (DHECD) has biological activity similar to brassinosteroids. In this study, we investigated the role of DHECD on the antioxidative enzyme activity and photosynthetic performance of rice subjected to high-temperature conditions. DHECD at either 1 or 10 µM was used as a foliar application to rice leaves at 23 days after sowing, and then, at 31 days after sowing, rice plants were moved to a heat chamber at 40/30 °C day/night for 9 days. Application of DHECD significantly increased the activities of the antioxidative enzymes: superoxide dismutase, catalase, peroxidase, and ascorbate peroxidase. The results of this study provide the first direct evident for DHECD-elevated antioxidative enzyme activity and decreased lipid peroxidation, which possibly induced thermotolerance in rice plants. Furthermore, DHECD was effective in increasing the net photosynthetic rate, stomatal conductance, and water use efficiency, as well as increasing the maximal quantum efficiency of photosystem II and decreasing non-photochemical quenching. Thus, enhancement of photosynthesis by DHECD application resulted in a high grain yield for rice plants subjected to high-temperature conditions.     

Excitation relaxation dynamics and energy transfer in fucoxanthin–chlorophyll a/c-protein complexes,probed by time-resolved fluorescence

In algae, light-harvesting complexes contain specific chlorophylls (Chls) and keto-carotenoids; Chl a, Chl c, and fucoxanthin (Fx) in diatoms and brown algae; Chl a, Chl c, and peridinin in photosynthetic dinoflagellates; and Chl a, Chl b, and siphonaxanthin in green algae. The Fx–Chl a/c-protein (FCP) complex from the diatom Chaetoceros gracilis contains Chl c₁, Chl c₂, and the keto-carotenoid, Fx, as antenna pigments, in addition to Chl a. In the present study, we investigated energy transfer in the FCP complex associated with photosystem II (FCPII) of C. gracilis. For these investigations, we analyzed time-resolved fluorescence spectra, fluorescence rise and decay curves, and time-resolved fluorescence anisotropy data. Chl a exhibited different energy forms with fluorescence peaks ranging from 677 nm to 688 nm. Fx transferred excitation energy to lower-energy Chl a with a time constant of 300 fs. Chl c transferred excitation energy to Chl a with time constants of 500–600 fs (intra-complex transfer), 600–700 fs (intra-complex transfer), and 4–6 ps (inter-complex transfer). The latter process made a greater contribution to total Chl c-to-Chl a transfer in intact cells of C. gracilis than in the isolated FCPII complexes. The lower-energy Chl a received excitation energy from Fx and transferred the energy to higher-energy Chl a. This article is part of a Special Issue entitled: Photosynthesis Research for Sustainability: Keys to Produce Clean Energy.     

Landscape Ideologies,Indigenous Governance,and Land Use Change in the Ecuadorian Amazon, 1960–1992

In recent years, states have ceded governance over large territories to indigenous organizations. This article examines the history of an early case of territorial governance (dating from the 1970s) to probe the social, political, and environmental processes that occur when an indigenous social movement becomes a governing body. It argues that indigenous organizations can quickly learn to “see like states” (Scott 1998) without adopting the particular visions promoted by the state that facilitated their new role. In the case explored here, indigenous leaders created landscape improvement schemes that went beyond those promoted by the state and others in terms of changing the legibility of land use and tenure categories. Furthermore, their schemes had significant impacts on forest cover as evidenced by remotely sensed images. These processes challenge theories that position the state as the primary arbitrator of human-environmental relations as well as theories that dichotomize between states and indigenous organizations.     

John Freeman,hay fever and the origins of clinical allergy in Britain, 1900–1950

In 1911, Drs John Freeman and Leonard Noon published an account of a novel treatment for hay fever. Their method of desensitisation consisted of injecting increasing doses of an extract of pollen subcutaneously until the hypersensitivity reaction was diminished or abolished. Over subsequent decades, desensitisation established itself as the cornerstone of clinical allergy in both England and the United States, at least until the advent of novel pharmaceutical agents in the 1950s and 1960s. Although British allergists such as Noon and Freeman were aware of conceptual developments within European immunology and pathology (such as the identification of anaphylaxis by Richet and Portier or von Pirquet’s coining of the term allergy), their approach to hay fever was driven by more immediate pragmatic, and indeed financial, considerations. Freeman’s immersion in the problems of hay fever and asthma and his pioneering use of allergen desensitisation or immunotherapy were shaped by his adherence to the convictions and bacteriological practices of his principal at St Mary’s Hospital, Almroth Wright, and by the drive to produce commercial vaccines which would help to subsidise the experimental and therapeutic work at St Mary’s. The aim of this paper is to explore early twentieth-century approaches to hay fever and other allergic diseases by tracing the intellectual and institutional origins of clinical allergy in Britain.     

Nitrogen fixation and transfer in open ocean diatom–cyanobacterial symbioses

Many diatoms that inhabit low-nutrient waters of the open ocean live in close association with cyanobacteria. Some of these associations are believed to be mutualistic, where N₂-fixing cyanobacterial symbionts provide N for the diatoms. Rates of N₂ fixation by symbiotic cyanobacteria and the N transfer to their diatom partners were measured using a high-resolution nanometer scale secondary ion mass spectrometry approach in natural populations. Cell-specific rates of N₂ fixation (1.15–71.5 fmol N per cell h⁻¹) were similar amongst the symbioses and rapid transfer (within 30 min) of fixed N was also measured. Similar growth rates for the diatoms and their symbionts were determined and the symbiotic growth rates were higher than those estimated for free-living cells. The N₂ fixation rates estimated for Richelia and Calothrix symbionts were 171–420 times higher when the cells were symbiotic compared with the rates estimated for the cells living freely. When combined, the latter two results suggest that the diatom partners influence the growth and metabolism of their cyanobacterial symbionts. We estimated that Richelia fix 81–744% more N than needed for their own growth and up to 97.3% of the fixed N is transferred to the diatom partners. This study provides new information on the mechanisms controlling N input into the open ocean by symbiotic microorganisms, which are widespread and important for oceanic primary production. Further, this is the first demonstration of N transfer from an N₂ fixer to a unicellular partner. These symbioses are important models for molecular regulation and nutrient exchange in symbiotic systems.     

How does elevated ozone impact soybean? A meta‐analysis of photosynthesis,growth and yield

Surface ozone concentrations ([O₃]) during the growing season in much of the northern temperate zone reach mean peak daily concentrations of 60 p.p.b. Concentrations are predicted to continue to rise over much of the globe during the next 50 years. Although these low levels of ozone may not induce visible symptoms on most vegetation, they can result in substantial losses of production and reproductive output. Establishing the vulnerability of vegetation to rising background ozone is complicated by marked differences in findings between individual studies. Ozone effects are influenced by exposure dynamics, nutrient and moisture conditions, and the species and cultivars that are investigated. Meta‐analytic techniques provide an objective means to quantitatively summarize treatment responses. Soybean has been the subject of many studies of ozone effects. It is both the most widely planted dicotyledonous crop and a model for other C₃ annual plants. Meta‐analytic techniques were used to quantitatively summarize the response of soybean to an average, chronic ozone exposure of 70 p.p.b., from 53 peer‐reviewed studies. At maturity, the average shoot biomass was decreased 34% and seed yield was 24% lower. Even in studies where [O₃] was < 60 p.p.b., there was a significant decrease in biomass and seed production. At low [O₃], decreased production corresponded to a decrease in leaf photosynthesis, but in higher [O₃] the larger loss in production was associated with decreases in both leaf photosynthesis and leaf area. The impact of ozone increased with developmental stage, with little effect on vegetative growth and the greatest effect evident at completion of seed filling. Other stress treatments, including UV‐B and drought, did not alter the ozone response. Elevated carbon dioxide significantly decreased ozone‐induced losses, which may be explained by a significant decrease in stomatal conductance.     

Effect of sulphate-limited growth on mitochondrial electron transfer and energy conservation between reduced nicotinamide–adenine dinucleotide and the cytochromes in Torulopsis utilis

1. Conditions have been established for the sulphate-limited growth of Torulopsis utilis in continuous culture. 2. Mitochondria prepared from sulphate-limited cells lack both piericidin A sensitivity and the first energy-conservation site (site 1). Sensitivity to antimycin A or cyanide and the second and third energy-conservation sites were apparently unaffected by sulphate-limited growth. 3. Aerobic incubation for 8h of sulphate-limited cells with a low concentration of sulphate (50mum or less) resulted in the recovery of mitochondrial piericidin A sensitivity and site 1. The use of higher concentrations of sulphate (250mum or more) still resulted in the recovery of mitochondrial piericidin A sensitivity and site 1, but also resulted in the appearance of a non-phosphorylating oxidase, which mediated oxidation of the respiratory chain at about the level of cytochrome b in an antimycin A- and cyanide-insensitive manner. Both this alternative route and the conventional normal route of respiration were shown to coexist and to intercommunicate at the level of cytochrome b. 4. Low-temperature spectroscopy failed to identify any new respiratory component to explain the alternative route. 5. The apparent affinity of the alternative route for oxygen was similar to that for the conventional route through cytochrome oxidase, namely half-maximal activity at 0.1mum-oxygen or less. 6. The non-haem iron concentration of submitochondrial particles was unaffected by sulphate limitation, whereas the acid-labile sulphide concentration was lowered tenfold. Marked increases (between four- and 30-fold) in the acid-labile sulphide concentration of submitochondrial particles were observed in sulphate-limited cells after aerobic incubation with various concentrations of sulphate. The lowest increase (fourfold) was observed without added sulphate, the highest (30-fold) with 1.0mm added sulphate. 7. The ratio of non-haem iron to acid-labile sulphide in submitochondrial particles varied with different growth conditions from a maximum of 15.0 to a minimum of 0.72. It is suggested that analytical measurements of non-haem iron are an inadequate guide to the concentration of iron-sulphur protein in complex systems. 8. The effects of sulphate-limited growth on site 1 and piericidin sensitivity are interpreted to indicate a role for iron-sulphur protein in these properties. 9. The aerobic incubation of sulphate-limited cells with cycloheximide resulted in the recovery by mitochondria of site 1 but not of piericidin sensitivity. 10. The appearance of the alternative route for cyanide- and antimycin-A (but not piericidin A-) insensitive respiration on incubating sulphate-limited cells with sulphate concentrations higher than 250mum indicates that the alternative route involves an iron-sulphur protein.     

Spatiotemporal dynamics of duck harvest distributions in the Central and Mississippi flyways, 1960–2019

Geographical distributions of waterfowl exhibit annual variation in response to spatiotemporal variation in weather conditions, habitat availability, and other factors. Continuing changes in climate and land use could lead to persistent shifts of waterfowl distributions, potentially causing a mismatch with habitat conservation planning, wetland restoration efforts, and harvest management decisions informed by historical distributions. We used band recoveries and harvest records (i.e., hunter-harvested wings) from the United States Fish and Wildlife Service Waterfowl Parts Collection Survey as indices of duck distribution in autumn and winter, and quantified intra-annual, interannual, and interspecific variation in their geographic distributions across 6 decades (1960–2019) for 15 duck species in the Central and Mississippi flyways in North America. Specifically, we tested for annual and decadal shifts in mean latitude and longitude of recoveries for each month (Oct–Jan) by species and taxonomic guild (i.e., dabbling, diving ducks). Overall, species varied in the extent, timing, and sometimes direction, of distributional change in recoveries. From 1960–2019, mean recovery locations for dabbling ducks shifted south 105–296 km in October and 27 km in November (wings only), whereas mean latitudes shifted north 144–234 km in December and 186–301 km in January. Mean recovery locations for diving ducks shifted north 162 km in October (wings only), 84–173 km in December, and 66–120 km in January, but shifted 99–512 km south in November. Shifts in longitude were less consistent between guilds and data types. Finally, distributional change rarely accelerated during recent decades, except for southward shifts of band recoveries of diving ducks in November and northward shifts of band and wing recoveries of dabbling ducks in January. Although anecdotal accounts of large-scale northward shifts in duck distributions are prolific in the land management and hunting communities, our data demonstrate more subtle shifts that vary considerably by species and month. Observed changes in recovery distributions could necessitate changes in timing of habitat management practices throughout the Central and Mississippi flyways and may result in fewer hunting and recreational opportunities for some species in southern states. Quantifying patterns of historical change is a necessary first step to understanding temporal and interspecific variation in waterfowl distributions, which will help with landscape-scale conservation and management efforts in the future and enable effective communication to core constituencies regarding ongoing changes and their implications for recreational engagement.     

Resonance energy transfer and competing processes in donor–acceptor of sodium zinc (II)-2,9,16,23-phthalocyanine tetracarboxylate molecule

An important issue that should be taken into consideration when applying the molecules in photodynamic therapy (PDT) of cancer is the occurrence of homo-resonance energy transfer process between them. We have determined the probability of energy transfer for sodium zinc (II)-2,9,16,23-phthalocyanine tetracarboxylate (ZnPc(COONa)₄) molecules in aqueous NaOH solution. The homo-quenching effect of the molecule was also measured by calculating the diffusion controlled bimolecular rate constant of k _q = 6.5?×?10⁹ M^?1s^?1, which did not show a significant competition with the rate constant of homo-resonance energy transfer process at the applied concentration of the molecules (6 μM). The Förster radius (R? ₀) for ZnPc(COONa)₄ molecules was calculated to be 42 Å. The availability of these calculations should facilitate the potential application of ZnPc(COONa)₄ molecule as an anticancer drug in PDT.