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Metabolic aspects of the relationship between the chloroplast and the photosynthetic cell.

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posted on 19.11.2015, 09:09 by Christopher B. Morris
The presence of phosphate and dicarboxylate translocators in the outer membranes of the chloroplast is based largely on work with spinach chloroplast suspensions. This project is a comparative study of the relationship between the chloroplast and the photo synthetic cell using isolated chloroplast suspensions from Spinacia (spinach), Pisum, (pea), Helianthus (sunflower), and Kalanchoe. The transport of photosynthetic intermediates across the outer chloroplast membranes was monitored using the technique of silicone-oil centrifugation. Uptake of radioactive metabolites was measured in assays similar to those employed by Heldt et al. The products of 14CO2 fixation were identified for each of the species, and their fate monitored in terms of export from or retention by the plastids. Assay conditions were altered to attempt to affect the distribution of photosynthetic products. Phosphate concentration was altered and photo synthetic metabolites added to the assay medium. For Spinacia investigation was made of the effect on distribution of photosynthate of alteration of bicarbonate concentration, temperature and osmolarity of bathing medium, and additions of MgCl2, MnCl2, CaCl2, NaCl, Na2SO4 and indoleacetic acid. The results of the investigations suggested the presence of a phosphate-translocator in chloroplasts of Spinacia, Pisum, and Helianthus, but there was no compelling evidence for the existence of such a translocator in the Kalanchoe chloroplast. The presence of a dicarboxylate translocator was demonstrated in Spinacia chloroplasts, but definite conclusions as to the presence of such a translocator in the other species were thwarted by probable enzymic contamination in the chloroplast suspensions.


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University of Leicester

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