Plant Physiol. Drug Metab Dispos
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Plant Physiology 88:207-212 (1988)
© 1988 American Society of Plant Biologists

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Metabolism and Enzymology

Effects of Temperature Pretreatment in the Dark on Photosynthesis of the Intact Spinach Chloroplast 1

Chee Fook Fu2 and Martin Gibbs

Institute for Photobiology of Cells and Organelles, Brandeis University, Waltham, Massachusetts 02254

Isolated, intact spinach (Spinacia oleracea L. var. "Long Standing Bloomsdale") chloroplasts were heated in the dark and the effect of this treatment on photosynthetic activities was determined at 25°C. Dark incubation of the chloroplasts for 10 minutes at 35°C and pH 8.1 resulted in a 50% decline in CO2 photoassimilation. This decline in photosynthetic performance was dependent upon time, temperature, and medium pH with the optimum effect at acidic pH values. Photosynthetic decline was not observed if MgATP, MgADP, or a mixture of fructose 1,6-bisphosphate, aldolase, and oxaloacetate or ribose 5-phosphate and oxaloacetate was added prior to but not after the temperature pretreatment. A chloroplast preparation reconstituted with thylakoids and stroma from pretreated (35°C, 10 minutes, pH 8.1) intact chloroplasts and supplemented with ferredoxin, ADP, and NADP was photosynthetically competent, indicating that ATP-coupled electron flow and the enzymes comprising the Benson-Calvin cycle remained stable during the dark treatment. In contrast, exposure of isolated thylakoids to 35°C for 10 minutes uncoupled photophosphorylation from NADP and ferricyanide reduction. We propose that the decline of intact chloroplast photosynthesis is the result of a decrease in the content of or a change in the ratios of the adenine nucleotides. Maintenance of an adequate supply of adenine nucleotide is the effect of the externally added MgATP or of chloroplastic respiration of a sugar phosphate.

2 Present address: Roche Institute of Molecular Biology, Nutley, NJ 07110.

1 Supported by National Science Foundation PCM 83-04147.






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Copyright © 1988 by the American Society of Plant Biologists