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 Sp ring/Cheyenne 7A) were used in experiments to investigate the kind of changes that take place in the photosynthetic apparatus of different w heat genotypes as a consequence of growing at low temperature. Using a PAM fluorometer, changes in the photochemical quenching were traced a t 2-degrees-C and 20-degrees-C. Although there was generally less phot ochemical quenching at low temperature than at room temperature, in th e case of the frost-resistant variety Cheyenne an increase in photoche mical quenching was observed at low temperature as a function of the l ength 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.