Botanisches Institut, Universität Düsseldorf, Universitätsstraße 1, D-4000, Düsseldorf, Federal Republic of Germany.
Planta. 1979 Oct;146(5):529-38. doi: 10.1007/BF00388828.
Exposure of spinach plants to high temperature (35° C) increased the heat resistance of the leaves by about 3° C. This hardening process occurred within 4 to 6 h, whereas dehardening at 20°/15° C required 1 to 2 days. At 5° C dehardening did not take place. Hardening and dehardening occurred in both the dark and the light. The hardiness was tested by exposure of the leaves to heat stress and subsequent measurements of chlorophyll fluorescence induction and light-induced absorbance changes at 535 nm on the leaves and of the photosynthetic electron transport in thylakoids isolated after heat treatment. Heat-induced damage to both heat-hardened and non-hardened leaves seemed to consist primarily in a breakdown of the membrane potential of the thylakoids accompanied by partial inactivation of electron transport through photosystem II. The increase in heat resistance was not due to temperature-induced changes in lipid content and fatty acid composition of the thylakoids, and no conspicuous changes in the polypeptide composition of the membranes were observed. Prolonged heat treatment at 35° C up to 3 days significantly decreased the total lipid content and the degree of unsaturation of the fatty acids of membrane lipids without further increase in the thermostability of the leaves. Intact chloroplasts isolated from heat-hardened leaves retained increased heat resistance. When the stroma of the chloroplasts was removed, the thermostability of the thylakoids was decreased and was comparable to the heat resistance of chloroplast membranes obtained from non-hardened control plants. Compartmentation studies demonstrated that the content of soluble sugars within the chloroplasts and the whole leaf tissue decreased as heat hardiness increased. This indicated that in spinach leaves, sugars play no protective role in heat hardiness. The results suggest that changes in the ultrastructure of thylakoids in connection with a stabilizing effect of soluble non-sugar stroma compounds are responsible for acclimatization of the photosynthetic apparatus to high temperature conditions. Changes in the chemical composition of the chloroplast membranes did not appear to play a role in the acclimatization.
菠菜植株暴露在高温（35°C）下，其叶片的耐热性提高了约 3°C。这个硬化过程在 4 到 6 小时内发生，而在 20°C/15°C 下脱硬化则需要 1 到 2 天。在 5°C 下，脱硬化不会发生。硬化和脱硬化在黑暗和光照中都发生。硬化和脱硬化通过叶片暴露在热应激下以及随后测量叶绿素荧光诱导和叶片 535nm 处的光诱导吸收变化以及热处理后分离的类囊体中的光合电子传递来测试。热硬化和未硬化叶片的热诱导损伤似乎主要包括类囊体膜电位的崩溃，同时伴随着通过光系统 II 的电子传递的部分失活。耐热性的增加不是由于类囊体的脂质含量和脂肪酸组成的温度诱导变化引起的，也没有观察到膜的多肽组成发生明显变化。在 35°C 下延长热处理时间长达 3 天会显著降低总脂质含量和膜脂脂肪酸的不饱和程度，而叶片的耐热性不会进一步提高。从热硬化叶片中分离的完整叶绿体保持了增加的耐热性。当去除叶绿体基质时，类囊体的热稳定性降低，并且与从未硬化对照植物中获得的叶绿体膜的耐热性相当。区室化研究表明，随着耐热性的增加，叶绿体和整个叶片组织中的可溶性糖含量降低。这表明在菠菜叶片中，糖在耐热性中没有保护作用。结果表明，与可溶性非糖基质化合物的稳定作用相关的类囊体超微结构的变化是光合作用装置适应高温条件的原因。叶绿体膜的化学成分变化似乎在适应过程中没有起作用。
