Ribonuclease Levels in the Mesocotyl Tissue of <i>Zea mays</i> as a Function of 2,4-Dichlorophenoxyacetic Acid Application

Abstract

The application of high concentrations of 2,4- (lichlorophenoxyacetic acid (2,4-D) to plants results in increased nucleic acid content (4, 11, 17, 22). The RNA synthesized is largely ribosomal (4,13). Since IAA will also induce increases in nucleic acids (6, 19) the auxin properties of 2,4-D are presunmably in- volved. If basal stem tissues of soybean (13) or corn (22) seedlings are incubated with appropriate con- centrations of 2,4-D a net synthesis of RNA can be obtained. With apical tissues this does not occur. High concentrations of the auxin prevent the (legra- dation of ribosomal andl soluble RNA that normally accompany the expansive growth of young cells but no synthesis is involved (9). A factor of unknown significance in this auxin-mediatecl RNA metabolism is ribonuclease(s) (RNase). There have been suggestions that RNases may have synthetic functions in plants (2, 8, 14). As cells expand there is an in- crease in RNase activity (3,6,8, 18); possibly the high RNase levels of older cells have something to do with the RNA synthesis enhanced by 2,4-D application. On the other hand, if RNases have solely degraclative functions, high concentrations of 2,4-D may block RNA degra(lation by inhibiting the enzymes or sup- pressing RNase synthesis. It appeared to us that studies on the level of RNase as a function of 2,4-D application were needed. This paper reports our findings froml such an investigation.