Yamamoto H Y, Kamite L, Wang Y Y
Department of Food Science and Technology, University of Hawaii, Honolulu, Hawaii 96822.
Plant Physiol. 1972 Feb;49(2):224-8. doi: 10.1104/pp.49.2.224.
A new ascorbate-induced chloroplast absorbance change which has the characteristics of a carotenoid shift is described. The absorbance change was light-dependent at pH 7 but not at pH 5. The difference spectra for the light and dark changes were similar, showing a large absorbance peak at 505 nanometers, smaller peaks near 468 and 437 nanometers, and a sharp valley around 483 nanometers. The absorbance change is assigned to violaxanthin de-epoxidation because various conditions affected the absorbance change and violaxanthin de-epoxidation similarly, and the difference spectrum resembled the spectrum of zeaxanthin minus violaxanthin in organic solvent.Nigericin with KCl inhibited the light-dependent change at 505 nanometers. This effect, as well as the dark change at pH 5, indicated that de-epoxidation requires an acidic condition in chloroplasts. The effects of 3-(3,4-dichlorophenyl)-1, 1-dimethyl urea, 2,6-dichlorophenolindophenol, and phenazine methosulfate indicated that the chloroplast acidification which mediates the 505 nanometers change is derived from hydrogen-ion transport linked to photosystem 1. Thus the 505 nanometers change could serve as an endogenous probe for chloroplast acidification and an indirect indicator of hydrogenion transport. At pH 5, the role of ascorbate appears to be to provide the reducing potential necessary for reductive de-epoxidation of violaxanthin. At pH 7, ascorbate could have an additional effect of stimulating electron transport and hence the hydrogen-ion transport necessary for de-epoxidation.In contrast to leaves and algae, de-epoxidation in chloroplasts was irreversible under the conditions investigated. Under some conditions other absorbance changes which were apparently due to chlorophyll were superimposed on the de-epoxidation change. The relationship of these ascorbate-induced changes to other absorbance changes observed in chloroplasts and green algae remains to be determined.
本文描述了一种新的抗坏血酸诱导的叶绿体吸光度变化，其具有类胡萝卜素转移的特征。该吸光度变化在pH 7时依赖于光，而在pH 5时则不依赖光。光变化和暗变化的差示光谱相似，在505纳米处有一个大的吸光度峰，在468和437纳米附近有较小的峰，在483纳米左右有一个尖锐的谷。该吸光度变化归因于紫黄质脱环氧化作用，因为各种条件对吸光度变化和紫黄质脱环氧化作用的影响相似，并且差示光谱类似于叶黄素减去紫黄质在有机溶剂中的光谱。尼日利亚菌素与氯化钾抑制了505纳米处的光依赖性变化。这种效应以及pH 5时的暗变化表明，脱环氧化作用需要叶绿体中的酸性条件。3-(3,4-二氯苯基)-1,1-二甲基脲、2,6-二氯酚靛酚和吩嗪硫酸甲酯的作用表明，介导505纳米变化的叶绿体酸化源自与光系统1相关的氢离子转运。因此，505纳米变化可作为叶绿体酸化的内源性探针和氢离子转运的间接指标。在pH 5时，抗坏血酸的作用似乎是提供紫黄质还原脱环氧化所需的还原电位。在pH 7时，抗坏血酸可能具有刺激电子传递的额外作用，从而促进脱环氧化所需的氢离子转运。与叶片和藻类不同，在所研究的条件下，叶绿体中的脱环氧化作用是不可逆的。在某些条件下，其他明显归因于叶绿素的吸光度变化叠加在脱环氧化变化上。这些抗坏血酸诱导的变化与叶绿体和绿藻中观察到的其他吸光度变化之间的关系仍有待确定。
