Characterization of Heat Injury in Grapes Using ¹H Nuclear Magnetic Resonance Methods

Abstract

Transverse relaxation times (T2) of tissue water ('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 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.Occurrence of injury from high temperature has been widely reported in many crop plants (14, 27). Temperatures slightly above optimum are generally known to cause physiological imbalance in plants by their direct effects on kinetics of chemical and biochemical reactions (14). Heat injury in plants has been attributed to protein denaturation and thus, the heat tolerance to thermal stability of proteins (2). However, a clear association of protein denaturation with heat injury is difficult to find in all cases (14). Nonetheless, many studies have suggested that lipid changes are associated with heat injury (17,22).Cellular membranes have been implicated as playing a key role in high temperature injury to plants. Although little is known about the effect of high temperatures on membranes, many studies suggest that the cell membranes are the locus of injury and that disintegration of cell membranes is associated with heat injury (3,15,18,21,28). There is overwhelming evidence that high temperature can disrupt membrane structure and, thus, the membrane-associated functions (3,22,24 (9,20,26) and to characterize heat and freezing injury in some plant tissues (19,21).The purpose of this investigation was to characterize heat injury in leaves and suspension cultured cells of grape using NMR methods. MATERIALS AND METHODS Plant MaterialStem cuttings from two cultivars of grape hybrids (Vitis spp. cv 'Veeblanc' and 'Venus') were collected from the Ashland Horticultural Farm, Kansas. The cuttings were planted in a mixture of peat moss and perlite (1:1 v/v) and held in the greenhouse under a mist until roots were initiated. The plants then were transplanted to larger pots and held in the greenhouse at 250C and 80% RH until use. Suspension Cultured CellsCallus cultures were initiated from stem sections. Explants were surface sterilized with 25% aqueous solution of Clorox (5.25% sodium hypochlorite) for 20 min and rinsed three times in sterile distilled water. Explants were grown on Schenk and Hildebrandt (23) solid medium containing 3.7 mg/L 1-naphthaleneacetic acid and 1.08 mg/L kinetin. Suspension cultured cells were initiated from 7-week-...

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Cold- or Heat-Tolerance of Leaves and Roots in Perennial Ryegrass Determined by1H-NMR

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High-temperature-induced Electrolyte Leakage from Excised Leaves and Roots of Three Hollies

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