The light induction of maize phosphoenolpyruvate carboxylase kinase translatable mRNA requires transcription but not translation

We have previously demonstrated that the level of translatable mRNA for phosphoenolpyruvate carboxylase kinase in maize leaves is increased in response to light (Hartwell et al, 1996; Plant Journal 10, 1071-1078). To identify the steps required for this increase, we have examined the effects of protein and RNA synthesis inhibitors. The RNA synthesis inhibitors actinomycin D and cordycepin (500 mu M) strongly inhibited the light-induced increases in kinase translatable mRNA and the apparent phosphorylation state of phosphoenolpyruvate carboxylase, as judged by its sensitivity to inhibition by L-malate, The protein synthesis inhibitors cycloheximide and puromycin blocked the light-induced increase in the apparent phosphorylation state of phosphoenolpyruvate carboxylase but not the increase in kinase translatable mRNA, Indeed, the amount of phosphoenolpyruvate carboxylase kinase translatable mRNA after 3 h of illumination of leaves treated with either 1 mM puromycin or 100 mu M cycloheximide was double that in illuminated control leaves. Each inhibitor reduced the light-induction of two control genes, malic enzyme and pyruvate, phosphate dikinase, Thus the light induction of phosphoenolpyruvate carboxylase kinase translatable mRNA requires RNA synthesis, but not protein synthesis.