Photosynthesis

About: Photosynthesis is a research topic. Over the lifetime, 19789 publications have been published within this topic receiving 895197 citations.

Predictions of Mn and Fe use efficiencies of phototrophic growth as a function of light availability for growth and of C assimilation pathway

Abstract: SUMMARY Iron is involved in many photosynthetic, respiratory and nitrogen assimilation reactions of plants as Fe bound tightly to polypeptides catalysing redox reactions. Manganese is involved as tightly bound Mn in photoreaction II of photosynthesis and in certain superoxide dismutases, while loosely bound Mn2+ is the unique activator of some enzymes, and is an alternative to Mg2+ in activating many enzymes. This paper uses data on the quantitative role of Fe and Mn in catalysts to predict the efficiency with which Fe and Mn are used in C assimilation [mol C assimilated (mol catalytic metal in enzyme)−1 s−1] and the metal cost of C assimilation [mol catalytic metal in enzyme (mol C assimilated)−1 s−1] in photolithotrophic growth in relation to genetic and environmental variables. The genetic variables were the relative content of thylakoid proteins in major taxa (cyanobacteria and red algae, chlorophytes and chromophytes) and smaller-scale taxonomic differences (various subtypes of C4 metabolism, and C3 metabolism, in terrestrial vascular plants). The environmental variables were the range of photon flux densities in which photolithotrophic growth of O2 evolvers can occur, and the inorganic C supply conditions controlling the repression/de-repression of the inorganic C concentrating mechanism in cyanobacteria and microalgae. The results of the computations yield the following conclusions. The largest predicted difference in Fe and Mn costs of photolithotrophic growth is related to changes in the photon flux density for growth. The predicted Fe cost increased 50-fold, and the Mn cost increased 80-fold, at the lowest extreme of photon flux density compared to the highest found naturally. The increase is partly countered by the larger ratio of light-harvesting pigments to thylakoid protein complexes assumed for the cells grown at low photon flux densities, although the extent of the increase in photosynthetic unit size is limited by considerations of efficiency of excitation energy transfer. However, the major influences are the higher pigment content in biomass enabling a larger fraction of incident light to the absorbed, and the sub-maximal specific reaction rates of redox catalysts (whose content is constrained via excitation energy transfer considerations) at very low photon flux densities. A smaller difference, four-fold or less, in Fe and Mn costs of photolithotrophic growth, is predicted by comparing major taxa (cyanobacteria plus red algae; chlorophytes plus chromophytes) with contrasting ratios of thylakoid redox catalysts. Differences in Fe and Mn costs of growth of less than two-fold are predicted when the Fe- and Mn-efficient organisms with CO2− concentrating mechanisms (C4 land plants; algae with active inorganic C influx) and high requirements for ATP relative to NADPH, are compared with organisms relying on CO2 diffusion from air or air-equilibrated solutions and C3 biochemistry. These predictions of variations in Fe and Mn costs of photolithotrophy have implications for the ecology of phototrophs.

More Productive Than Maize in the Midwest: How Does Miscanthus Do It?

Abstract: In the first side-by-side large-scale trials of these two C(4) crops in the U.S. Corn Belt, Miscanthus (Miscanthus x giganteus) was 59% more productive than grain maize (Zea mays). Total productivity is the product of the total solar radiation incident per unit land area and the efficiencies of light interception (epsilon(i)) and its conversion into aboveground biomass (epsilon(ca)). Averaged over two growing seasons, epsilon(ca) did not differ, but epsilon(i) was 61% higher for Miscanthus, which developed a leaf canopy earlier and maintained it later. The diurnal course of photosynthesis was measured on sunlit and shaded leaves of each species on 26 dates. The daily integral of leaf-level photosynthetic CO(2) uptake differed slightly when integrated across two growing seasons but was up to 60% higher in maize in mid-summer. The average leaf area of Miscanthus was double that of maize, with the result that calculated canopy photosynthesis was 44% higher in Miscanthus, corresponding closely to the biomass differences. To determine the basis of differences in mid-season leaf photosynthesis, light and CO(2) responses were analyzed to determine in vivo biochemical limitations. Maize had a higher maximum velocity of phosphoenolpyruvate carboxylation, velocity of phosphoenolpyruvate regeneration, light saturated rate of photosynthesis, and higher maximum quantum efficiency of CO(2) assimilation. These biochemical differences, however, were more than offset by the larger leaf area and its longer duration in Miscanthus. The results indicate that the full potential of C(4) photosynthetic productivity is not achieved by modern temperate maize cultivars.

Cyanobacterial conversion of carbon dioxide to 2,3-butanediol

Abstract: Conversion of CO2 for the synthesis of chemicals by photosynthetic organisms is an attractive target for establishing independence from fossil reserves. However, synthetic pathway construction in cyanobacteria is still in its infancy compared with model fermentative organisms. Here we systematically developed the 2,3-butanediol (23BD) biosynthetic pathway in Synechococcus elongatus PCC7942 as a model system to establish design methods for efficient exogenous chemical production in cyanobacteria. We identified 23BD as a target chemical with low host toxicity, and designed an oxygen-insensitive, cofactor-matched biosynthetic pathway coupled with irreversible enzymatic steps to create a driving force toward the target. Production of 23BD from CO2 reached 2.38 g/L, which is a significant increase for chemical production from exogenous pathways in cyanobacteria. This work demonstrates that developing strong design methods can continue to increase chemical production in cyanobacteria.