Full TGIF Record # 4905
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Publication Type:
i
Refereed
Author(s):Berkowitz, Gerald A.; Gibbs, Martin
Author Affiliation:Institute for Photobiology of Cells and Organelles, Brandeis University, Waltham, Massachusetts
Title:Reduced osmotic potential inhibition of photosynthesis
Source:Plant Physiology. Vol. 72, No. 3, August 1983, p. 1100-1109.
Publishing Information:Lancaster, PA: American Society of Plant Physiologists
Keywords:TIC Keywords: Osmosis; Photosynthesis; Metabolites; Stress; Carbon cycle
Abstract/Contents:The effects of reduced reaction medium osmotic potential (0.67 molar sorbitol as compared to a control treatment with 0.33 molar sorbitol) on the enzymic steps of the photosynthetic carbon reduction cycle were investigated using isolated spinach (Spinacia oleracea L. var Longstanding of photosynthetic rates by a stromal alkalating agent (NH4Cl) was associated with specific steps of the cycle. Low osmotic potential induced stromal acidification was found to be facilitated by osmotically induced chloroplast shrinkage. However, the action of the alkalating agent was found not to be associated with reversal of osmotically induced morphological changes of the stromal compartment. Labeled metabolite analyses indicated that the osmotics stress treatment caused the substrate for fructose 1,6-bisphosphatase (FBPase) to build up in the absence of NH4Cl, and the substrate for phosphoribulokinase to increase in the presence of NH4Cl. These data were interpreted as indicating that the most severe effect of osmotic stress on photosynthesis is at the site of FBPase, and that this inhibition is mediated by osmoticaly induced stromal acidification. Phosphoribulokinase activity inhibition at the low osmotic potential treatment was apparently less sever and not mediated by stromal acidification. A third site of osmotic inhibition, which was reversed by NH4Cl, and therefore was assumed to be mediated by stromal acidification, was at the step of ribulose 1,5-biphosphate carboxylase. Additions of NH4Cl also enhanced the activity of the pH-insensitive phase of the photosynthetic carbon reduction cycle, 3-phosphoglyceric acid reduction, at the stress treatment. This effect was thought to be mediated by the removal of the block at FBPase. A model was proposed to outline the relative severity of osmotic stress effects at various sites of the photosynthetic carbon reduction cycle.
Language:English
References:22
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ASA/CSSA/SSSA Citation (Crop Science-Like - may be incomplete):
Berkowitz, G. A., and M. Gibbs. 1983. Reduced osmotic potential inhibition of photosynthesis. Plant Physiol. 72(3):p. 1100-1109.
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