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Photoregulation of Phosphoenolpyruvate Carboxylase in Salsola soda L. and Other C₄ Plants ¹

Laboratory of Plant Physiology, University of Patras, Patras, Greece

Photoactivation of phosphoenolpyruvate carboxylase was found to occur in several, though not all, C₄ species examined; Salsola soda L. was used for a detailed study of this effect of light.

Activity differences between light and darkness are maximized when glycerol (25% v/v) is included in the extraction medium and in the absence of mercaptoethanol. In plants grown in the growth chamber, the night-form of the enzyme, in addition to low activity, shows a positive cooperativity (with phosphoenolpyruvate), which is gradually abolished by light of increasing intensities. This allosteric behavior is absent in plants adapted to a high light environment. Activation and deactivation, under light and darkness respectively, are quite fast, suggesting post-translational regulation. The photoactivation appears to depend on photosynthetic electron flow, since it is saturated at high photon fluxes (around 1000 microeinsteins per square meter per second) and inhibited by 3-(3,4-dichlorophenyl)-1,1-dimethylurea.

¹ The final stage of this work was financially supported by the National Research Foundation of Greece.

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