Heat sensitivity of chloroplasts and leaves: Leakage of protons from thylakoids and reversible activation of cyclic electron transport
Heat sensitivity of chloroplasts and leaves: Leakage of protons from thylakoids and reversible activation of cyclic electron transport
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DOI：
10.1023/a:1006149317411
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发表时间：
1999-01-01
影响因子：
3.7
通讯作者：
Heber, U
中科院分区：
文献类型：
--
作者：
Bukhov, NG;Wiese, C;Heber, U
在光照完整的菠菜叶绿体，升温到40摄氏度以上增加了质子渗透性的类囊体之前，通过光系统II的线性电子传递被抑制。同时，抗霉素A敏感的循环电子传递周围光系统II被激活与氧气或CO2，但不与亚硝酸盐作为电子受体。在40至42摄氏度之间，循环电子传递的激活平衡了质子的损失，从而维持了相当大的跨类囊体质子梯度。当变暗的菠菜叶的温度缓慢增加到40摄氏度时，光系统II的醌受体Q（A）的还原增加，特别是当呼吸CO2产生和质体醌的自氧化通过将大气的氧含量从21%降低到1%而被抑制时。同时，光系统II活性部分丧失。叶温降低到20 ℃后，暗Q（A）降低的增强消失。在黑暗中加热叶片期间，通过光散射测量没有检测到膜破裂。在照射菠菜叶，光散射和非光化学猝灭的叶绿素荧光增加升温至约40摄氏度，而光系统II的活动失去了，这表明额外的类囊体膜，是无关的光系统II功能。P700经远红光氧化后，在黑暗中还原呈双相性。它被加速的因素高达10（快速组件），甚至25（慢组件）后，短期热暴露的叶子。在20 ℃时，当厌氧或KCN被用来抑制还原剂的呼吸氧化时，观察到类似的加速。甲基紫精从光系统II的还原侧接受电子，完全消除了远红光后热诱导的P700（+）还原加速。数据表明，将分离的叶绿体或完整的菠菜叶的温度提高到约40摄氏度不仅抑制了通过光系统II的线性电子流，而且还激活了光系统I驱动的循环电子传递途径，该途径能够促进类囊体质子梯度。根据光系统I依赖的基质片层和基粒边缘的循环电子传递，讨论了远红氧化后P700（+）还原动力学的异质性。
In illuminated intact spinach chloroplasts, warming to and beyond 40 degrees C increased the proton permeability of thylakoids before linear electron transport through Photosystem II was inhibited. Simultaneously, antimycin A-sensitive cyclic electron transport around Photosystem II was activated with oxygen or CO2, but not with nitrite as electron accepters. Between 40 to 42 degrees C, activation of cyclic electron transport balanced the loss of protons so that a sizeable transthylakoid proton gradient was maintained. When the temperature of darkened spinach leaves was slowly increased to 40 degrees C, reduction of the quinone acceptor of Photosystem II, Q(A), increased particularly when respiratory CO2 production and autoxidation of plastoquinones was inhibited by decreasing the oxygen content of the atmosphere from 21 to 1%. Simultaneously, Photosystem II activity was partially lost. The enhanced dark Q(A) reduction disappeared after the leaf temperature was decreased to 20 degrees C. No membrane energization was detected by light-scattering measurements during heating the leaf in the dark. In illuminated spinach leaves, light scattering and nonphotochemical quenching of chlorophyll fluorescence increased during warming to about 40 degrees C while Photosystem II activity was lost, suggesting extra energization of thylakoid membranes that is unrelated to Photosystem II functioning. After P700 was oxidized by far-red light, its reduction in the dark was biphasic. It was accelerated by factors of up to 10 (fast component) or even 25 (slow component) after short heat exposure of the leaves. Similar acceleration was observed at 20 degrees C when anaerobiosis or KCN were used to inhibit respiratory oxidation of reductants. Methyl viologen, which accepts electrons from reducing side of Photosystem II, completely abolished heat-induced acceleration of P700(+) reduction after far-red light. The data show that increasing the temperature of isolated chloroplasts or intact spinach leaves to about 40 degrees C not only inhibits Linear electron flow through Photosystem II but also activates Photosystem I-driven cyclic electron transport pathways capable of contributing to the transthylakoid proton gradient. Heterogeneity of the kinetics of P700(+) reduction after far-red oxidation is discussed in terms of Photosystem I-dependent cyclic electron transport in stroma lamellae and grana margins.