The effect of temperature and light on photoinhibition, carbon metabolism and freezing tolerance: A survey of winter and spring wheat cultivars

The process of cold acclimation and the subsequent acquisition of maximum freezing tolerance occurs only if plants grow and develop at low temperatures in the presence of light. Therefore, photosynthesis is an absolute requirement for successful cold acclimation. In this survey of 10 arbitrarily chosen winter and spring wheat cultivars, of unknown freezing tolerance, the morphology, susceptibility to low temperature photoinhibition and the maximum capacities and/or amounts of some of the major regulatory photosynthetic enzymes were examined. Relative to spring wheat grown under cold acclimation conditions, cold acclimated winter wheat developed a compact growth habit and had higher NADP-MDH capacity. Cold acclimated winter wheat cultivars were consistently less susceptible to low temperature photoinhibition than spring wheat cultivars grown under identical conditions. Interestingly, SPS apparent amounts were higher in both winter and spring wheat cultivars grown under high excitation pressure conditions relative to low excitation pressure conditions. Plant breeders are continually trying to increase freezing tolerance in winter cereals without compromising productivity and disease resistance. Morphological markers such as compact growth are traditionally used as indicators of freezing tolerance. I demonstrate in this thesis that susceptibility to photoinhibition of cold acclimated winter wheat can be used to screen cultivars for freezing tolerance.