The degradation of ribonucleic acid in the cotyledons of Pisum arvense

Abstract

A ribonuclease has been partially purified from the cotyledons of germinating seed of Pisum arvense. The enzyme degrades ribopolynucleotides to adenosine 3[image]''-phosphate, guanosine 3[image]-phosphate and the cyclic nucleotides cytidine 2[image], 3[image]- phosphate and uridine 2[image], 3[image]-phosphate; no resistant[image]core [image] remains. The activity of RNA-degrading enzymes in the cotyledons increases to a maximum during the first 5 days of germination, passes through a minimum around the 8th day, and thereafter increases again. Ion-exchange chromatography of methanol- soluble extracts of cotyledons revealed the presence, amongst other components, of the 2[image], 3[image]- and 5[image]-phosphates of cytidine and uridine, the 3[image]- and 5[image]-phosphates of adenosine, and guanosine 5[image]-phosphate. Seed soaked in a solution containing [32p] orthophosphate gave a methanol-soluble fraction containing labelled nucleoside 5[image]-phosphates, but nucleoside 2[image]- and 3[image]-phosphates were not labelled. It is believed that the nucleoside 2[image]- and 3[image]-phosphates arise by the action of ribonuclease on cotyledon RNA.