CHARACTERIZATION OF HEAT INJURY IN GRAPES USING H-1 NUCLEAR-MAGNETIC-RESONANCE METHODS - CHANGES IN TRANSVERSE RELAXATION-TIMES

Transverse relaxation times (T2) of tissue water (H-1) in leaves and suspension cultured cells of grape hybrids (Vitis spp. cv 'Venus' and 'Veeblanc') were measured by nuclear magnetic resonance at various temperatures. The tissue water was characterized by two T2 time constants. A sharp decrease in T2 for the major fraction of tissue water was observed in association with heat injury, as measured by electrolyte leakage and triphenyltetrazolium chloride reduction in both leaves and suspension cultured cells. The changes in T2 as a result of heat injury were irreversible, as indicated by a temperature dependent hysteresis of T2. Studies using a paramagnetic probe (Mn+2) indicated that the plasma membrane was irreversibly damaged at the killing temperature, resulting in a loss of cell compartmentalization. Tissue water in heat-killed samples was characterized by only a single T2.