Irrungen, Wirrungen? The Mehler reaction in relation to cyclic electron transport in C3 plants

被引:152
作者
Heber, U [1 ]
机构
[1] Univ Wurzburg, Julius von Sachs Inst, D-97082 Wurzburg, Germany
关键词
D; Arnon; K; Asada; cyclic electron transport; U; Heber; AH Mehler; Mehler reaction; photoprotection; Photosystem II; water-water cycle;
D O I
10.1023/A:1020459416987
中图分类号
Q94 [植物学];
学科分类号
071001 ;
摘要
Plants not only evolve but also reduce oxygen in photosynthesis. Considerable oxygen uptake occurs during photorespiration of C3 plants. Controversies exist on whether direct oxygen reduction in the Mehler reaction together with associated electron transport is also a major sink of electrons when leaves are exposed to sunlight. Here, preference is given to the view that it is not. Whereas photorespiration consumes ATP, the Mehler reaction does not. In isolated chloroplasts photosynthesizing in the presence of saturating bicarbonate, the Mehler reaction is suppressed. In the water - water cycle of leaves, which includes the Mehler reaction, water is oxidized and electrons flow through Photosystems II and I to oxygen producing water. The known properties of coupled electron transport suggest that the water - water cycle cannot act as an efficient electron sink. Rather, by contributing to thylakoid acidification it plays a role in the control of Photosystem II activity. Cyclic electron transport competes with the Mehler reaction for electrons. Both pathways can help to defray possible ATP deficiencies in the chloroplast stroma, but play a more important role by making intrathylakoid protein protonation possible. This is a necessary step for the dissipation of excess excitation energy as heat. Linear electron flow to oxygen relieves the inhibition of cyclic electron transport, which is observed under excessive reduction of intersystem electron carriers. In turn, cyclic electron transport replaces functions of the linear pathway in the control of Photosystem II when oxygen reduction is decreased at low temperatures or, experimentally, when the oxygen concentration of the gas phase is low. Thus, cyclic electron flow acts in flexible relationship with the water - water cycle to control Photosystem II activity.
引用
收藏
页码:223 / 231
页数:9
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