TEMPERATURE AND CHEMICAL SHOCKS INDUCE CHILLING TOLERANCE IN GERMINATING CUCUMIS-SATIVUS (CV-POINSETT-76) SEEDS

Roots of 24-h-old germinated cucumber (Cucumis sativus cv. Poinsett 76 ) seeds were subjected to thermal and chemical stresses, equilibrated at 25 degrees C for 2 h and chilled at 2.5 degrees C for 96 h. The ger minated seeds were then held at 25 degrees C for 72 h after they were chilled and the elongation of the primary root was used as a measure o f chilling tolerance. Control roots elongated from an initial length o f 0.2 cm to a final length of 6.3 cm at the end of 72 h, while chilled roots elongated to a final length of only 0.4 to 0.6 cm. Exposure to 0.4 M ethanol for 4 h or to 40 degrees C for 1 h induced substantial c hilling tolerance and the roots had a final length of 4.1 and 3.1 cm, respectively. Exposure to 7.5 degrees C for 3 h conferred less chillin g tolerance (elongation to 1.4 cm), while exposure to other chemicals (i.e. aqueous solutions of Ca(NO3)(2), mannitol, methanol and NaCl) pr oduced less, though still significant increases in chilling tolerance. a more severe chilling treatment of 144 h at 2.5 degrees C was requir ed to consistently induce elevated rates of ion leakage. Only the heat and the ethanol shock treatments significantly reduced chilling-induc ed ion leakage. Inclusion of the protein synthesis inhibitor cyclohexi mide negated the protective effects of these shock treatments. It appe ars that de novo protein synthesis is required for induction of chilli ng tolerance by a variety of chemical and thermal shock treatments.