Reversible or Irreversible Change of Molecular Dynamics of Water in Pea Seedlings Exposed to Heaat Stress

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Influences of heat stress on epicotyls of per (Pisum sativum L.) plants were investigated by using non-destructive method. NMR spin-lattice relaxation time (T1), indicating molecular dynamics of water, was determined in tall type, cv. Alaska and dwarf type, cv. Progress No.9 seedlings grown under light condition. In no-elongation zone for both fresh cultivars a rapid decrease in T1 occured in the tissues exposed to 20-30℃ while rapid increase folloed by gradual decrease occured in T1 for the tissues exposed to 20-40℃ during a heat-cool cycle. On the other hand, in heat-denatured dead tissues, T1 linearly corresponded. FUrther, when pea plants were heated for 5h at 20-30℃ or 20-40℃ thermal hysteresis changes in T1 corresponding temperature in the subsequent heat-cool cycles was notably different. Epicotyls exposed to 30℃ treatments did not show temperature dependency whole those of the tissues exposed to 40℃ indicated temperature dependency. After the subsequent heat-cool cycles, the former was alive, the latter indicated tissue necrosis. Therefore, the change in T1 of epicotyls observed within 1h was considered a fast adaption or morality in cells to heat stress, and a temperature dependency of T1 in the subsequent heat-cool cycles clearly reflected tissue viability in per epicotyls. In conclusion, T1 on thermal response can be used as indicator of reversible or irreversible injurity in an intact plant.
九州大学の論文