The degradation of ribonucleic acid in the cotyledons of Pisum arvense.

1. A ribonuclease has been partially purified from the cotyledons of germinating seed of Pisum arvense. 2. The enzyme degrades ribopolynucleotides to adenosine 3'-phosphate, guanosine 3'-phosphate and the cyclic nucleotides cytidine 2',3'-phosphate and uridine 2',3'-phosphate; no resistant ;core' remains. 3. 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 eighth day, and thereafter increases again. 4. Ion-exchange chromatography of methanol-soluble extracts of cotyledons revealed the presence, amongst other components, of the 2'-, 3'- and 5'-phosphates of cytidine and uridine, the 3'- and 5'-phosphates of adenosine, and guanosine 5'-phosphate. 5. Seed soaked in a solution containing [(32)P]orthophosphate gave a methanol-soluble fraction containing labelled nucleoside 5'-phosphates, but nucleoside 2'- and 3'-phosphates were not labelled. 6. It is believed that the nucleoside 2'- and 3'-phosphates arise by the action of ribonuclease on cotyledon RNA.