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

The application of high concentrations of 2,4dichlorophenoxyacetic 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 presumably involved. If basal stem tissues of soybean (13) or corn (22) seedlings are incubated with appropriate concentrations 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 degradation of ribosomal and 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-mediated 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 increase 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 degradative functions, high concentrations of 2,4-D may block RNA degradation by inhibiting the enzymes or suppressing 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 from such an investigation.