GENETIC-STUDIES OF ANTIFREEZE PROTEINS AND THEIR CORRELATION WITH WINTER SURVIVAL IN WHEAT

Antifreeze proteins (AFPs) accumulate in the leaves of winter cereals during cold acclimation, where they may inhibit ice recrystallization during freezing and thawing cycles and provide nonspecific disease res istance. In this study, 21 wheat chromosome substitution lines and the parental lines Chinese Spring and Cheyenne wheat were used to determi ne the heritability of AFPs and the relationship between the accumulat ion of AFPs and winter survival. In cold-acclimated lines, antifreeze activity in leaf apoplastic extracts ranged from 1 (low) to 5 (high) w ith an average value of 3.2, and the accumulation of apoplastic protei ns ranged from 30 mu g (g FW)(-1) to 115 mu g (g FW)(-1) with a mean v alue of 70 mu g (g FW)(-1). Examination of the individual lines reveal ed that Cheyenne chromosomes 5B and 5D carry major regulatory genes th at increase both antifreeze activity and the accumulation of antifreez e proteins in plants grown at low temperature. Substitution lines carr ying Cheyenne chromosomes 2A, 3A, 6B, and 7A exhibited lower freezing tolerance and also showed a marked decrease in the accumulation of spe cific AFPs during cold acclimation. Antifreeze activity and apoplastic protein content were not correlated with freezing tolerance (defined as % survival at -11 degrees C), but they were both significantly and positively correlated with winter field survival rates. Antifreeze act ivity (positively correlated) and total leaf fresh weight (negatively correlated) together accounted for about 55% of the variation in winte r survival, indicating that high antifreeze activity and slow vegetati ve growth at low temperature are both important quantitative traits fo r winter survival.