Generation and suppression of microsomal ribonuclease activity after treatments with auxin and cytokinin.

RNase activity was assayed in subcellular fractions of apical regions of Pisum sativum L. var. Alaska epicotyls after seedling decapitation and treatments with various growth regulators. High concentrations of applied indoleacetic acid caused a marked increase to occur in the RNase activity level associated with "heavy" microsomes, e.g., a 20-fold rise per unit RNA or protein in 3 days. This rise could be abolished by treating with the cytokinin benzyladenine along with indoleacetic acid. Nevertheless, indoleacetic acid and benzyladenine acted synergistically in their abilities to evoke swelling and net synthesis of RNA and protein. Polysomal profiles prepared after treatment with indoleacetic acid plus benzyladenine showed less degradation than profiles from any other treatment. It is concluded that auxin generates and cytokinin suppresses the activity of a particular membrane-bound RNase which can control turnover of the auxin-evoked polysomes required for growth in peas. Synergism between the two hormones in this system may be explained by the action of one to increase RNA synthesis and the other to decrease RNA destruction.