Title

Regulation of Photosynthetic Carbon Reduction Cycle by Ribulose Bisphosphate and Phosphoglyceric Acid

Document Type

Article

Publication Date

11-1-1991

Publication Source

Plant Physiology

Abstract

The activation states of a number of chloroplastic enzymes of the photosynthetic carbon reduction cycle and levels of related metabolites were measured in leaves of sugar beet (Beta vulgaris L., Klein E-type multigerm) under slowly changing irradiance during a day. The activation states of both phosphoribulokinase and NADP+-glyceraldehyde-3-phosphate dehydrogenase increased early in the light period and remained constant during the middle of the day. Initial ribulose 1,5-bisphosphate carboxylase activity was already about one third of the midday level, did not change for the first 2 hours, but then increased in parallel with the rate of carbon fixation. Because the activation states increased by turns, first phosphoribulokinase and NADP+-glyceraldehyde-3-phosphate dehydrogenase and later ribulose 1,5-bisphosphate carboxylase, the ratios of the activation states changed remarkably. Levels of ribulose bisphosphate and phosphoglycerate, which were high enough to affect enzyme reaction rates and changed in concert with activation state, indicate that these metabolites are involved in feedback/feedforward regulation of enzymes of carbon assimilation. This regulatory sequence is able to explain how the reaction rates for the enzymes of carbon assimilation are adjusted to maintain their activities in balance with each other and with the flux of carbon fixation.

Inclusive pages

1115-1121

ISBN/ISSN

0032-0889

Publisher

American Society of Plant Biologists

Volume

97

Peer Reviewed

yes

Issue

3

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