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Photosynthesis
About: Photosynthesis is a research topic. Over the lifetime, 19789 publications have been published within this topic receiving 895197 citations.
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TL;DR: The first challenge is presented by the properties of ribulose bisphosphate carboxylase-oxygenase (Rubisco), which accounts for almost 50% of the world's photosynthesis as discussed by the authors.
Abstract: Aquatic photosynthetic microorganisms account for almost 50% of the world's photosynthesis ([19][1]). These organisms face several challenges in acquiring CO2 from the environment. The first challenge is presented by the properties of ribulose bisphosphate carboxylase-oxygenase (Rubisco). Rubisco is
269 citations
TL;DR: Reactions involving only the long wave photosystem, such as TPN reduction with ascorbate as electron donor and photooxidation of cytochromec by detergent‐treated chloroplasts were sensitive to a lower degree.
Abstract: — An attemlpt was made to localize the site of photoinhibition of photosynthesis by measuring the decay of various chloroplast reactions after exposure to very strong light. A11 substrate reductions coupled to oxygen evolution as well as photophosphorylation mediated by PMS, proved equally sensitive to photoinhibition. Reactions involving only the long wave photosystem, such as TPN reduction with ascorbate as electron donor and photooxidation of cytochromec by detergent-treated chloroplasts were sensitive to a lower degree.
Photoinhibition irreversibly annihilated the ‘variable’ fraction of fluorescence emission —it decreased the steady state yield 2-3 fold and abolished the slow rise of the emission at the onset of illurnination.
It is concluded that the primary site of light inactivation is in, or close to, the trapping centers of the oxygen evolving step of photosynthesis. Pre-illumination leaves these traps in a state capable of draining light from sensitizing pigments but unable to perform useful photochemistry.
268 citations
TL;DR: In this paper, Triton X-100 at pH 6.3 has been used to purify a PS2 fraction with very high rates of oxygen evolution (1000 μmol.h−1).
267 citations
TL;DR: Evidence that C4 photosynthesis can function within a single photosynthetic cell in terrestrial plants is provided and it is shown that Borszczowia aralocaspica (Chenopodiaceae) has the photosynthesis features of C4 plants, yet lacks Kranz anatomy.
Abstract: An important adaptation to CO2-limited photosynthesis in cyanobacteria, algae and some plants was development of CO2-concentrating mechanisms (CCM). Evolution of a CCM occurred many times in flowering plants, beginning at least 15-20 million years ago, in response to atmospheric CO2 reduction, climate change, geological trends, and evolutionary diversification of species. In plants, this is achieved through a biochemical inorganic carbon pump called C4 photosynthesis, discovered 35 years ago. C4 photosynthesis is advantageous when limitations on carbon acquisition are imposed by high temperature, drought and saline conditions. It has been thought that a specialized leaf anatomy, composed of two, distinctive photosynthetic cell types (Kranz anatomy), is required for C4 photosynthesis. We provide evidence that C4 photosynthesis can function within a single photosynthetic cell in terrestrial plants. Borszczowia aralocaspica (Chenopodiaceae) has the photosynthetic features of C4 plants, yet lacks Kranz anatomy. This species accomplishes C4 photosynthesis through spatial compartmentation of photosynthetic enzymes, and by separation of two types of chloroplasts and other organelles in distinct positions within the chlorenchyma cell cytoplasm.
267 citations
TL;DR: The analysis presented here suggests that the evolution of Rubisco is confined to an effectively one-dimensional landscape, which is manifested in simple power law correlations between its kinetic parameters, and appears to be tuned to the intracellular environment in which it resides such that the net photosynthesis rate is nearly optimal.
Abstract: Rubisco (D-ribulose 1,5-bisphosphate carboxylase/oxygenase), probably the most abundant protein in the biosphere, performs an essential part in the process of carbon fixation through photosynthesis, thus facilitating life on earth. Despite the significant effect that Rubisco has on the fitness of plants and other photosynthetic organisms, this enzyme is known to have a low catalytic rate and a tendency to confuse its substrate, carbon dioxide, with oxygen. This apparent inefficiency is puzzling and raises questions regarding the roles of evolution versus biochemical constraints in shaping Rubisco. Here we examine these questions by analyzing the measured kinetic parameters of Rubisco from various organisms living in various environments. The analysis presented here suggests that the evolution of Rubisco is confined to an effectively one-dimensional landscape, which is manifested in simple power law correlations between its kinetic parameters. Within this one-dimensional landscape, which may represent biochemical and structural constraints, Rubisco appears to be tuned to the intracellular environment in which it resides such that the net photosynthesis rate is nearly optimal. Our analysis indicates that the specificity of Rubisco is not the main determinant of its efficiency but rather the trade-off between the carboxylation velocity and CO2 affinity. As a result, the presence of oxygen has only a moderate effect on the optimal performance of Rubisco, which is determined mostly by the local CO2 concentration. Rubisco appears as an experimentally testable example for the evolution of proteins subject both to strong selection pressure and to biochemical constraints that strongly confine the evolutionary plasticity to a low-dimensional landscape.
267 citations