The Biosphere (original) (raw)
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Within a conceptional framework based on carbon metabolism oscillatory model (CMOM), diurnal variations of δ 13 С values of water-soluble organic matter (WSOM), and waterinsoluble organic matter (IOM) in leaves, stem and phloem sap of castor bean plants (Ricinus communis L.), experimentally investigated by Gessler et al. (2008), are discussed. It is shown that carbon for the synthesis of the IOM fraction components is provided by carbohydrate pool formed in carboxylase phase of photosynthetic oscillations and is enriched with 12 С due to carbon isotope effect in ribulosebisphosphate (RuBP) carboxylation. Carbon source for the synthesis of the WSOM fraction components is predominantly linked with carbohydrate pool formed in oxygenase phase of photosynthetic oscillations. They are enriched with 13 С due to carbon isotope effect in glycine dehydrogenase reaction. As a result, IOM fraction is always more enriched in 12 С in comparison with WSOM fraction. IOM fraction appears to be the main source of organic matter for the phloem sap. The organic substances of the sap are mainly used by plants to synthesize heterotrophic organ biomass thus determining the 13 С enrichment of heterotrophic organs (roots, seeds, wood) of plants in relation to autotrophic (leaves, needles) ones. In accordance with CMOM, the variations of δ 13 С values of WSOM and IOM fractions could be used for photosynthesis and assimilate transport and partitioning studies in real-time mode during the day.
Carbon isotope fractionation in plants
Phytochemistry, 1981
Plants with the C?, C, and crassulacean acid metabolism (CAM) photosynthetic pathways show characteristically different discriminations against 13C during photosynthesis. For each photosynthetic type, no more than slight variations are observed within or among species. CAM plants show large variations in isotope fractionation with temperature, but other plants do not. Different plant organs, subcellular fractions and metabolites can show widely varying isotopic compositions. The isotopic composition of respired carbon is often different from that of plant carbon, but it is not currently possible to describe this effect in detail. The principal components which will affect the overall isotope discrimination during photosynthesis are diffusion of CO,, interconversion of CO, and HCO;, incorporation of CO, by phosphoenolpyruvate carboxylase or ribulose bisphosphate carboxylase, and respiration. The isotope fractionations associated with these processes are summarized. Mathematical models are presented which permit prediction of the overall isotope discrimination in terms of these components. These models also permit a correlation of isotope fractionations with internal CO, concentrations. Analysis of existing data in terms of these models reveals that CO, incorporation in C, plants is limited principally by ribulose bisphosphate carboxylase, but CO, diffusion also contributes. In C, plants, carbon fixation is principally limited by the rate of CO, diffusion into the leaf. There is probably a small fractionation in C, plants due to ribulose bisphosphate carboxylase.
Russian Journal of Plant Physiology, 2000
Experimental data available in literature on changes in the carbon isotopic composition of biochemical fractions and metabolites isolated from plant biomass (Clusia minor) and photosynthesizing algae (Chlorella stigmatophora) under the action of environmental stress factors are reviewed and analyzed. Within the framework of previously suggested mechanism of carbon isotope fractionation in photosynthesis, all studied fractions and metabolites obtained from plants and photosynthesizing algae can be divided into two groups according to their carbon isotope composition. The first group includes the fractions and metabolite pools that contain carbon stored by cell during the carboxylase phase of Rubisco functioning. The second group consists of those formed primarily by the photorespiratory carbon flow, generated during the oxygenase phase of Rubisco functioning. The first group represents the "assimilatory" branch of photosynthesis and is enriched in 12 C relative to carbon of biomass, whereas the second group represents the "photorespiratory" branch and is enriched in 13 C. Under the action of environmental stress factors, such as incident light intensity, moisture availability, and salinity; the isotope composition of metabolites and fractions changes, which reflects variable contributions of the "assimilatory" and "photorespiratory" flows to the metabolite synthesis. These isotope shifts were used to study biochemical adaptation of plants to stress conditions and to elucidate the role of photorespiration in this adaptation.
5.1: Overview of Photosynthesis
2015
All living organisms on earth consist of one or more cells. Each cell runs on the chemical energy found mainly in carbohydrate molecules (food), and the majority of these molecules are produced by one process: photosynthesis. Through photosynthesis, certain organisms convert solar energy (sunlight) into chemical energy, which is then used to build carbohydrate molecules. The energy used to hold these molecules together is released when an organism breaks down food. Cells then use this energy to perform work, such as cellular respiration.
Carbon Isotope Discrimination And Photosynthesis
Annual Review of Plant Physiology and Plant Molecular Biology, 1989
Annu. Rev. Plant Physiol. Plant Mol. Bioi. 1989. 40:503-37 Copyright © 1989 by Annual Reviews Inc. All rights reserved ... GD Farquhar,l 1. R. Ehleringer,2 and KT Hubic ... IResearch School of Biological Sciences, Australian National University, Canberra, ACT 2601 Australia ...