Abstract
Our previous research with purified PEPC-PK suggested a possible redox regulation via thioredoxin. Through our several experiments of the oxidative-stress treatment in plants, we demonstrate the occurrence of this regulation in vivo. When maize plant was exposed to a cold stress under light, the degree of phosphorylation of PEPC was abruptly decreased. And when detached maize leaves were treated either with DCMU or diamide, the phosphorylation state changed similarly. Thus PEPC-PK activity seemed to be somehow inhibited under the stress. Succeeding experiments with cell extracts from stressed leaves revealed that the PEPC-PK activity could be recovered by incubation with dithiothreitol. Although previous studies suggested a rapid turn-over rate of PEPC-PK, our data showed that the PEPC-PK activity is not lost by degradation but redox-regulated in a reversible manner at least under oxidative stress conditions. Possible significance of redox regulation in the cytosol will be discussed.
