Fundamental studies on the actual condition of heat stress and its avoiding mechanism in crop plants

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In order to clarify the actual condition of heat stress, the realtime changes of leaf temperature in some crop plants were tracked visually by using thermotracter and analyzed its relations with stomatal aperture, transpiration rate and photosynthetic rate. The main results obtained were summarized as follows ;1.The flag leaf of a spring wheat (var.Haruyutaka) had more stomata on adaxial side than on abaxial side, and the opening and shutting movement of stomata were dull on abaxial side. In the daytime, the leaf surface temperature changed almost parallel with the changes in air temperature, accompanied with transpiration rate, and higher on abaxial side than on adaxial side.2.The leaf surface temperature of adaxial side of kidney bean (Phaseolus vulgaris L.) changed with changes in the leaf inclination, suggesting that the solar tracking movement of leaf plays an important role on the avoiding of heat stress. However, the leaf surface temperature of abaxial side were relatively stable regardless of leaf inclination under non-water stress conditions.3. The two potato varieties with different root mass, Norin 1 (large) and Konafubuki (small), were grown under two soil water conditions, wet and dry, and analyzed the effect of root mass and soil water conditions on leaf temperature. The leaf temperature was higher in dry plot than in wet plot, and the differences of leaf temperature between wet and dry plots was 3.3ﾟC for Konafubuki and 2.2ﾟC for Norin 1. The leaf temperature increased linearly with the increase in air temperature, accompaning with transpiration rate. The photosynthetic rate decreased because of the closing of stomata, due to water stress in plant under high air temperature conditions.