Characterization of heat injury in grapes using h nuclear magnetic resonance methods : changes in transverse relaxation times.

Transverse relaxation times (T(2)) of tissue water ((1)H) 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 T(2) time constants. A sharp decrease in T(2) 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 T(2) as a result of heat injury were irreversible, as indicated by a temperature dependent hysteresis of T(2). 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 T(2).