Control of gene expression during induction of cultured peanut cells: mRNA levels, protein synthesis and enzyme activity of stilbene synthase.

Stilbene synthase is an inducible enzyme occurring in a small number of plants. The enzyme is amenable to analysis and biochemical studies only after the cells are subjected to induction. Cell suspension cultures of peanut react very selectively if elicited with biotic inducers. Just as intact peanut plants produce stilbene phytoalexins when attacked by fungi so also do sterile cultured cells when treated with sterilized insoluble fungal cell walls. Both systems react by synthesizing stilbene synthase. The time courses of increase in enzyme activity, protein synthesis and mRNA activity were studied, and their relation to other activities of the cells was elaborated. The results show that, after applying the fungal elicitor, the system responds very quickly and selectively: within 2 hours the synthesis rate of stilbene synthase protein is increased more than 30-fold, the increase being detectable 40 min after induction. The first increase in translatable mRNA for stilbene synthase can be seen 20 min after application of the stimulus. Stilbene synthase synthesized in vivo was compared to stilbene synthase prepared by translation in vitro. There was no difference in size, and limited proteolysis did not indicate significant differences in the peptide structure of the primary translation product and the active enzyme.