Light Activation of Phosphoenolpyruvate Carboxylase in Maize Mesophyll Protoplasts

Abstract

The effect of light on phosphoenolpyruvate (PEP) carboxylase (EC 4.1.1.31) activity in maize (Zea mays L. cv. Ganga 5) mesophyll protoplasts was examined. When protoplasts were illuminated in a lowbuffered (2 mM) medium, there was a 20-35% increase in the activity of PEP carboxylase over that in darkness. There was no light activation, however, if the protoplasts were kept in a high-buffered (20 mM) medium. Maximum activation occurred after 10-15 min of illumination and the activation was lost within 8 min after transfer to darkness. The light activation of PEP carboxylase was completaly suppressed by phlorizin or CCCP, but not by DCMU. The characteristics of the light activated form of PEP carboxylase in protoplasts (in situ) differed slightly from those observed with leaves (in vivo). We suggest that light-induced alkalization of the cytosol and ATP formation are involved in the activation of PEP carboxylase, possibly through phosphorylation of the enzyme. © 1992, Gustav Fischer Verlag, Stuttgart. All rights reserved.