Lehrstuhl Botanik I, Botanisches Institut der Universität, Mittlerer Dallenbergweg 64, D-8700, Würzburg, Germany.
Planta. 1980 Jul;149(2):170-5. doi: 10.1007/BF00380879.
The role of monovalent cations in the photosynthesis of isolated intact spinach chloroplasts was investigated. When intact chloroplasts were assayed in a medium containing only low concentrations of mono- and divalent cations (about 3 mval l(-1)), CO2-fixation was strongly inhibited although the intactness of chloroplasts remained unchanged. Addition of K(+), Rb(+), or Na(+) (50-100 mM) fully restored photosynthesis. Both the degree of inhibition and restoration varied with the plant material and the storage time of the chloroplasts in "low-salt" medium. In most experiments the various monovalent cations showed a different effectiveness in restoring photosynthesis of low-salt chloroplasts (K(+)>Rb(+)>Na(+)). Of the divalent cations tested, Mg(2+) also restored photosynthesis, but to a lesser extent than the monovalent cations.In contrast to CO2-fixation, reduction of 3-phosphoglycerate was not ihibited under low-salt conditions. In the dark, CO2-fixation of lysed chloroplasts supplied with ATP, NADPH, and 3-phosphoglycerate strictly required the presence of Mg(2+) but was independent of monovalent cations. This finding excludes a direct inactivation of Calvin cycle enzymes as a possible basis for the inhibition of photosynthesis under low-salt conditions.Light-induced alkalization of the stroma and an increase in the concentration of freely exchangeable Mg(2+) in the stroma, which can be observed in normal chloroplasts, did not occur under low-salt conditions but were strongly enhanced after addition of monovalent cations (50-100 mM) or Mg(2+) (20-50 mM).The relevance of a light-triggered K(+)/H(+) exchange at the chloroplast envelope is discussed with regard to the light-induced increase in the pH and the Mg(2+) concentration in the stroma, which are thought to be obligatory for light activation of Calvincycle enzymes.
研究了单价阳离子在分离完整菠菜叶绿体光合作用中的作用。当完整叶绿体在仅含有低浓度的一价和二价阳离子（约 3 mval l(-1)）的培养基中进行测定时，尽管叶绿体的完整性保持不变，但 CO2 固定受到强烈抑制。添加 K(+)、Rb(+)或 Na(+)（50-100 mM）可完全恢复光合作用。抑制程度和恢复程度随植物材料和叶绿体在“低盐”培养基中的储存时间而变化。在大多数实验中，各种单价阳离子在恢复低盐叶绿体光合作用方面表现出不同的效果（K(+)>Rb(+)>Na(+)）。在所测试的二价阳离子中，Mg(2+)也能恢复光合作用，但程度低于单价阳离子。与 CO2 固定相反，在低盐条件下，3-磷酸甘油酸的还原不受抑制。在黑暗中，用 ATP、NADPH 和 3-磷酸甘油酸供应裂解叶绿体的 CO2 固定严格需要 Mg(2+)的存在，但与单价阳离子无关。这一发现排除了卡尔文循环酶的直接失活作为低盐条件下光合作用抑制的可能基础。在正常叶绿体中可以观察到基质的光诱导碱化和基质中可自由交换的 Mg(2+)浓度的增加，但在低盐条件下不会发生，而在添加单价阳离子（50-100 mM）或 Mg(2+)（20-50 mM）后会强烈增强。考虑到光诱导的叶绿体包膜上的 K(+)/H(+)交换与光诱导的基质中 pH 和 Mg(2+)浓度的增加有关，这被认为是卡尔文循环酶光激活的必需条件，因此讨论了光触发的 K(+)/H(+)交换的相关性。
