COLD-INDUCED CHANGES IN THE POLYSOME PATTERN AND PROTEIN-SYNTHESIS INWINTER RYE (SECALE-CEREALE) LEAVES

Cold-induced changes in the polysome pattern and protein synthesis wer e analyzed in winter rye, Secale cereale L. cv. Voima, during one week 's cold stress treatment, which was performed by transferring the 7-da y-old plants from the greenhouse (25-degrees-C, long-day conditions) t o 3-degrees-C and a photoperiod of 10.5 h. Freezing resistance determi ned by electrolyte leakage increased significantly upon cold stress st arting from LT50 value -5-degrees-C and reaching -9-degrees-C on the d ay 7 of cold exposure. After 4 weeks at low temperature, plants reache d an LT50 of -12-degrees-C. The polysome content increased markedly du ring cold stress compared to the control plants. After 2 weeks of cold treatment the polysome content decreased to the same level as that in control plants. The size-class distribution of polysomes showed a hig h proportion of large protein synthesizing polysomes in cold-stressed plants. After 2 weeks the values were comparable to those in control p lants. Cold-induced proteins were detected using S-35-labelled methion ine for in vitro translations. At least 2 new polypeptides, M(r) 30000 and 18 000, were induced on the first day of cold stress and continue d to be expressed at low temperatures 4 weeks later.