CHARACTERIZATION OF COLD HARDENING IN WHEAT USING FLUORESCENCE INDUCTION PARAMETERS

Two types of wheat varieties (Triticum aestivum L. cv. Cheyenne and cv. Chinese Spring, with strong and poor frost resistance, respectively) and two substitution lines (Chinese Spring/Cheyenne 5A and Chinese Spring/Cheyenne 7A) were used in experiments to investigate the kind of changes that take place in the photosynthetic apparatus of different wheat genotypes as a consequence of growing at low temperature. Using a PAM fluorometer, changes in the photochemical quenching were traced at 2-degrees-C and 20-degrees-C. Although there was generally less photochemical quenching at low temperature than at room temperature, in the case of the frost-resistant variety Cheyenne an increase in photochemical quenching was observed at low temperature as a function of the length of the hardening period. This seems to indicate the existence of a regulating mechanism that ensures that even at low temperature the plant will be capable of an adequate level of photosynthesis.