Effect of X-Irradiation on Nucleic Acids in Zea mays: II. On the Level of Ribonuclease Activity in Growing Seedlings

Abstract

X-Irradiation of dry Z mays seeds greatly enhances the activity of RNase in growing seedlings, especially in the meristematic tissue (root tip and mesocotyl). Meristematic cells normally have a low level of RNase activity, but the activity increases with cell growth and maturation. The RNase activity of root tips grown from X-irradiated seeds is enhanced as much as fivefold. The distribution of RNase among the subcellular components of root tissue is not affected by X-irradiation. X-Irradiation reduces the RNase activity in the scutellum, a storage tissue, which is consistent with the reduced utilization of scutellar RNA. Studies on the incorporation of P32 into the nucleotides by in vitro degradation of endogenous root tip RNA shows that incorporation is primarily into the pyrimidine nucleoside di- and triphosphates. EDTA stimulates RNase activity in root tip and mesocotyl homogenates but has little effect on scutellum homogenates.