A COMPARISON OF FREEZING-INJURY IN OAT AND RYE - 2 CEREALS AT THE EXTREMES OF FREEZING TOLERANCE

A detailed analysis of cold acclimation of a winter rye (Secale cereal e L. cv Puma), a winter oat (Avena sativa L. cv Kanota), and a spring oat cultivar (Ogle) revealed that freezing injury of leaves of nonaccl imated seedlings occurred at -2 degrees C in both the winter and sprin g cultivars of oat but did not occur in winter rye leaves until after freezing at -4 degrees C. The maximum freezing tolerance was attained in all cultivars after 4 weeks of cold acclimation, and the temperatur e at which 50% electrolyte leakage occurred decreased to -8 degrees C for spring oat, -10 degrees C for winter oat, and -21 degrees C for wi nter rye. In protoplasts isolated from leaves of nonacclimated spring oat, expansion-induced lysis was the predominant form of injury over t he range of -2 to -4 degrees C. At temperatures lower than -4 degrees C, loss of osmotic responsiveness, which was associated with the forma tion of the hexagonal Il phase in the plasma membrane and subtending l amellae, was the predominant form of injury. In protoplasts isolated f rom leaves of cold-acclimated oat, loss of osmotic responsiveness was the predominant form of injury at all injurious temperatures; however, the hexagonal II phase was not observed. Rather, injury was associate d with the occurrence of localized deviations of the plasma membrane f racture plane to closely appressed lamellae, which we refer to as the ''fracture-jump lesion.'' Although the freeze-induced lesions in the p lasma membrane of protoplasts of spring oat were identical with those reported previously for protoplasts of winter rye, they occurred at si gnificantly-higher temperatures that correspond to the lethal freezing temperature.