Repression of isoperoxidase formation in excised tobacco pith by exogenous, auxin-controlled RNA

Abstract

Previous work has shown that tobacco pith tissue contains two constitutive isoperoxidases migrating toward the anode at pH 9·0. Within 24 hr of aseptic culture on basal medium, such tissue develops five new isoperoxidases, three cathodic and two anodic. The appearance of the new isoperoxidases involves de novo protein formation; it is inhibited by anaerobic conditions, by such inhibitors as Actinomycin D, and by the plant hormone indole-3-acetic acid (IAA). We now find that phenol RNA extracted from parent pith and injected or vacuum infiltrated into cultured pith explants prevents the appearance of the new isozymes; RNA from cultured pith has no such effect. Hydrolysis with 0·3 N KOH, ribonuclease or proteolytic enzymes partially destroys this activity, while treatment with both ribonuclease and proteolytic enzymes completely destroys it. Fractionation of the RNA indicates that part of the repressor activity is associated with an mRNA-like fraction.