STUDIES IN SEED DORMANCY

S ummary The nucleic acids of the cotyledons of hazel ( Corylus avellana L.) seeds have been extracted by a modified phenol method and subsequently fractionated on a methylated serum albumin‐kieselguhr (MAK) column. Fractions which appear to contain soluble RNA ( s RNA), ribosomal RNA ( r RNA) and messenger RNA ( m RNA) have been found in addition to one which contains both DNA and RNA (DNA‐RNA). During the first 10 days after imbibition there was little nucleic acid synthesis in seeds kept at either 4° C or 20° C. However, changes in the s RNA appear to have occurred at both temperatures and the formation of additional s RNA from other nucleic acid molecules has also been inferred. It is suggested that imbibition may result in the activation of a postulated stable and inactive form of s RNA occurring in the dry seed. Imbibition also induced the appearance of the light and heavy fractions of r RNA. After 10 days at 4° C 20 % of the seeds were able to germinate at 20° C. Further chilling caused a substantial fall in seed dormancy together with considerable nucleic acid synthesis. It would appear that nucleic acid synthesis does not play a part early in the process of breaking hazel seed dormancy by chilling, but it is possible that it plays a part at a later stage of the process. Seeds, chilled at 4° C for 50 days and then transferred to 20° C for 5 days showed an apparently large increase in the rate of cotyledonary nucleic acid metabolism. A net fall in the content of r RNA and DNA‐RNA was also found.