Hormonal Control of Senescence of Bean Endocarp: Auxin-suppression of RNase.

Time course studies indicate that auxin prevents senescence of excised bean endocarp (Phaseolus zvlgaaris, L.. var. Kentucky Wonder pole beans) through an effect on metabolism of RNA. Firstly, during aging of tissue sections in absence of auxin degradation of RNA precedes degradation of DNA and protein: these degradations are prevented by auxin (4, 5, /7).. Secondly, during short (2-hr) incubations of tissue sections auxin enhances synthesis of RNA before enhancement of protein synthesis can be detected (Sacher, unpublished results). Additionallv, during incubations of 15 to 24 hr auxin causes a substantial net synthesis of both RNA and protein, which is inhibited by actinomycin D (6). That net synthesis is manifested in each of 6 subcellular fractions (8) indicates that auxin controls synthesis of all cellular RNA and protein. As a result of an auxin-induced net synthesis of RNA and a loss of RNA in absence of auxin, there is a large difference in RNA content between waterand auxin-aged tissue. Recent studies (with Dr. Ann Matthysse, unpublished) indicate that this difference cannot be accounted for when chromatin is prepared from endocarp aged 15 hr with and without auxin, and assayed for template activity in presence of E. coli RNA polymerase. In 3 experiments with separate batches of tissue there was no difference in template activity between waterand auxin-aged tissue, notwithstanding auxin-aged tissue having 30 to 80 % more RNA than water-aged tissue. In this paper are presented results showing that auxin causes a substantial decrease in RNase during aging of tissue sections. This action of auxin is consistent with hitherto observed effects of auxin on RNA and protein synthesis during aging of bean endocarp. Bean endocarp sections were prepared and used for assay of RNase and content of RNA and protein at zero time and after aging for 15 hr with and without atuxin (a-naphthaleneacetic acid, NAA). The sections were washed in running tap water for