Activity and Compartmentation of Photosynthetic Carboxylases in Normal and Chloroplast-mutant Maize Leaves |
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Authors: | ANNA H-NAGY MARIA PACSÉRY ÁGNES FALUDI-DÁNIEL |
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Institution: | Department of Evolution and Genetics, Eötvös University and Institute of Plant Physiology of the Hungarian Academy Budapest, Hungary |
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Abstract: | The activity of ribulose-l,5-diphosphate carboxylase (RudiP-carboxylase) and phosphoenolpyruvate carboxylase (PEP-carboxylase) measured in vitro was independent from the chlorophyll content of the leaves. The relatively high activity of PEP-carboxylase as compared to the RudiP-carboxylase activity was particularly pronounced in the mutants. Realization of the potential (in vitro measured) carboxylating activities in fixation of CO2in vivo was practically complete in normal leaves. In the mutants, however, CO2 fixation was lower than the level permitted by the carboxylase activity. This could be explained only in part by the impaired rate of photophosphorylation. Compartmentation of PEP-carboxylase was different in normal and mutant leaves: in contrast to the normal ones, parenchyma-sheath cells of the mutants exhibited high PEP-carboxylase activity. Competition of PEP-carboxylase with RudiP-carboxylase for CO2 in the mutants led to accumulation of organic acids, and can account for their low photosynthetic activity. |
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