Regulation of Photosynthetic Carbon Metabolism in Isolated Spinach Chloroplasts Under Photorespiratory and Non-Photorespiratory Conditions
Gruenewald, Patricia Jane
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https://hdl.handle.net/2142/77656
Description
Title
Regulation of Photosynthetic Carbon Metabolism in Isolated Spinach Chloroplasts Under Photorespiratory and Non-Photorespiratory Conditions
Author(s)
Gruenewald, Patricia Jane
Issue Date
1983
Department of Study
Plant Biology
Discipline
Botany
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Biology, Plant Physiology
Language
eng
Abstract
The regulatory aspects of several added metabolites on photosynthetic carbon metabolism in isolated spinach chloroplasts were examined. Under conditions of ambient O(,2), saturating HCO(,3)('-) and a range of phosphate concentrations (0.1-10 mM), PGA and DHAP (1-6 mM each) reduced ('14)CO(,2) fixation by 60% of the control rate when the ratio of triose phosphate (TP): phosphate (ie., DHAP: phosphate, PGA: phosphate, or (DHAP + PGA): phosphate) exceeded 8. Ratios of TP: phosphate greater than 6 prevented light activation of RuBP carboxylase.
The response of Calvin cycle intermediates in isolated spinach chloroplasts to photorespiratory and non-photorespiratory conditions of O(,2) and CO(,2) was also examined. A chamber was designed and constructed in which low levels (10-30 (mu)M) of ('14)CO(,2) could be achieved and sustained in suspensions of chloroplasts. Any desired O(,2) concentration could be maintained concurrently within the chamber. The system design permitted rapid sampling of the chloroplast suspension which was essential to the accurate quantitation and identification of photosynthetic intermediates. Using this system, it was determined that excretion of glycolate by isolated chloroplasts occurred at the same rate (8 (mu)mol/mg chl/hr) under both non-photorespiratory and photorespiratory O(,2) conditions. Glycolate formation under non-photorespiratory conditions was determined to be light dependent and was inhibited by photophosphorylation inhibitors. Light activation of RuBP carboxylase was unaffected by O(,2) tension. Glycolate formation at both 2% and 21% O(,2) was sensitive to changes in phosphate concentration. High phosphate concentration (1 mM) inhibited the rate of glycolate formation at 2% O(,2) by 52% and at 21% O(,2) by 64% of the control rate. At this phosphate concentration, control ('14)CO(,2) fixation was inhibited 18% and 54% at 2% O(,2) and 21% O(,2), respectively. In the presence of 0.5 mM phosphate, the addition of unlabelled glycerate (1 mM) to the chloroplast suspension also reduced the rate of glycolate formation at both 2% and 21% O(,2).
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