United States Department of Agriculture/Agricultural Research Service, University of Illinois, Urbana, Illinois 61801.
Plant Physiol. 1985 Apr;77(4):956-62. doi: 10.1104/pp.77.4.956.
Stomatal conductance is coupled to leaf photosynthetic rate over a broad range of environmental conditions. We have investigated the extent to which chloroplasts in guard cells may contribute to this coupling through their photosynthetic activity. Guard cells were isolated by sonication of abaxial epidermal peels of Vicia faba. The electrochromic band shift of isolated guard cells was probed in vivo as a means of studying the electric field that is generated across the thylakoid membranes by photosynthetic electron transport and dissipated by photophosphorylation. Both guard cells and mesophyll cells exhibited fast and slow components in the formation of the flash-induced electrochromic change. The spectrum of electrochromic absorbance changes in guard cells was the same as in the leaf mesophyll and was typical of that observed in isolated chloroplasts. This observation indicates that electron transport and photophosphorylation occur in guard cell chloroplasts. Neither the fast nor the slow component of the absorbance change was observed in the presence of the uncoupler carbonylcyanide p-trifluoromethoxy-phenylhydrazone which confirms that the absorbance change was caused by the electric field across the thylakoid membranes. The magnitude of the fast rise was reduced by half in the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea. Therefore, photosystem II is functional and roughly equal in concentration to photosystem I in guard cell chloroplasts. The slow rise was abolished by 2,5-dibromo-3-methyl-6-isopropyl-1,4-benzoquinone indicating the involvement of the cytochrome b(6)/f complex in electron transport between the two photosystems. Relaxation of the absorbance change was irreversibly retarded in cells treated with the energy transfer inhibitor, N,N'-dicyclohexylcarbodiimide. The slowing of the rapid decay kinetics by N,N'-dicyclohexylcarbodiimide confirms that the electrical potential across the thyalkoid membrane is dissipated by photophosphorylation. These results show that guard cell chloroplasts conduct photosynthetic electron transport in a manner similar to that in mesophyll cells and provide the first evidence that photophosphorylation occurs in guard cells in vivo.
在广泛的环境条件下，气孔导度与叶片光合速率相耦合。我们研究了叶绿体在保卫细胞中的光合作用活性在多大程度上促成了这种耦合。通过对蚕豆下表皮的离体细胞进行超声处理，分离出保卫细胞。通过活体探测分离的保卫细胞的电致变色带位移，研究由光合作用电子传递产生并通过磷酸化消耗的跨类囊体膜的电场。保卫细胞和叶肉细胞都在闪光诱导的电致变色变化中表现出快速和慢速成分。保卫细胞的电致变色吸收变化的光谱与叶肉细胞相同，与分离的叶绿体观察到的光谱相似。这一观察结果表明，电子传递和磷酸化发生在保卫细胞的叶绿体中。在解偶联剂羰基氰化物对三氟甲氧基苯腙存在的情况下，没有观察到吸收变化的快速或慢速成分，这证实了吸收变化是由跨类囊体膜的电场引起的。在 3-（3,4-二氯苯基）-1,1-二甲基脲存在的情况下，快速上升的幅度减少了一半。因此，在保卫细胞叶绿体中，光系统 II 是功能性的，并且与光系统 I 的浓度大致相等。2,5-二溴-3-甲基-6-异丙基-1,4-苯醌使缓慢上升消失，表明电子在两个光系统之间的传递涉及细胞色素 b(6)/f 复合物。用能量转移抑制剂 N,N'-二环己基碳二亚胺处理细胞后，吸收变化的弛豫不可逆地减缓。N,N'-二环己基碳二亚胺使快速衰减动力学减慢，证实跨类囊体膜的电势通过磷酸化消耗。这些结果表明，保卫细胞叶绿体以类似于叶肉细胞的方式进行光合作用电子传递，并提供了活体中磷酸化发生在保卫细胞中的第一个证据。
