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Effect of Root-zone Temperature on the Physiology of Leaf Lettuce (Lactuca sativa L.)
Juang, Nae Yiing
25℃、30℃ 及 35℃ 之根溫處理 12 天，探討其生長與生理之變化。
和根部鮮重及乾重於 25℃、30℃ 根溫處理間，大多無顯著差異；35℃時
此二品系的生長量明顯較 25℃ 或 30℃ 者為低。30℃ 高根溫下白粉品
，於35℃時均顯著低於 25℃、30℃。35℃ 根溫下，地上部及根部之呼吸
The thermostability of leaf-tissue membrane of seventen lettuce cultivars grown in a greenhouse was assessed by measuring electrolyte leakage of the tissue for specific intervals during a 60 minute period at 50℃ . Results indicated that the differential responses among cultivars, exhibited at 50℃ for 10 minutes , were most significant and were selected for the subsequent assessment of leaf-tissue heat injury.Among the cultivars tested , Improved Green Leaf (IGL) was found to be the most heat tolerant while White Power (WP) was the most heat sensitive . Two cultivars of lettuce , IGL and WP, were used to investigate the physiological changes and growth rates in solution at 25, 30, and 35℃. Results showed that the growth of both shoot and root were reduced by supraoptimal temperature of 35℃. The growth inhibition were more pronounced on WP than IGL at 35℃ root-zone temperature. The photosynthetic rate and water potential of the leaves were found to decrease with rising root-zone temperature up to 35℃. No significant differences in chlorophyll levels were observed among treatments. Increasing root temperature resulted in higher respiration rate and activity of roots . The respiration rate and activity of excised root were markedly enhanced as the root-zone temperature was raised to 35℃ and thus leading to more carbohydrate consumption in the root. This, in turn ,increased the export of sugar from shoot, and soluble carbohydrate accumulated in the root. The contents of free amino acids, the activity of peroxidase and the production of ethylene were increased significantly by exposing to 35℃ root-ozone temperature. The result indicated that the supraoptimal root temperature may induced the root senescence leading to inhibition of shoot growth.
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