Daniell H, Anbudurai P R, Periyannan S, Renganathan M, Bhardwaj R, Kulandaivelu G, Gnanam A
Biochem Biophys Res Commun. 1985 Feb 15;126(3):1114-21. doi: 10.1016/0006-291x(85)90301-8.
Studies on the appearance of various electron transport functions were followed during greening of etiolated cucumber cotyledons. Appearance of dichlorodimethoxy-p-benzoquinone, dimethyl quinone, tetramethyl-p-phenylenediamine, dichlorophenol indophenol and ferricyanide Hill reactions were observed after 8h of greening. However, photoreduction of methyl viologen (MV) and nicotinamide adenine dinucleotide phosphate (NADP) was observed from 2h of greening. Variable fluorescence, which is a direct indication of water-splitting function, was observed from 2h of greening in cotyledons, thylakoid membranes and photosystem II (PSII) particles. The decrease in variable fluorescence in the presence of MV (due to rapid reoxidation of Q-) observed from early stages of greening confirmed the photoreduction of MV by PSII. The early development of water-splitting function was further confirmed by the abolition of variable fluorescence in thylakoid membranes and PSII particles by heat treatment and concomittant loss of light dependent oxygen uptake in the presence of MV in heat treated chloroplasts. However, the photoreduction of MV and NADP was insensitive to intersystem electron transport inhibitors, dichlorophenyl dimethylurea or dibromomethyl isopropyl-p-benzoquinone till 8h of greening. Though the oxidation of intersystem electron carrier cytochrome f was observed from early stages of greening, the reduction of cytochrome f was not observed till 8h of greening. All these observations confirm that during early stages of greening MV and NADP are photoreduced by PSII without the involvement of intersystem electron carriers or the collaboration of PSI. Since these observations are at variance with the currently prevalent concept (Z-Scheme) of the photosynthetic generation of reducing power, which requires definite collaboration of the two photosystems, an alternate electron flow pathway is proposed.
在黄化黄瓜子叶变绿过程中，对各种电子传递功能的出现情况进行了研究。变绿8小时后，观察到二氯二甲氧基对苯醌、二甲基醌、四甲基对苯二胺、二氯酚靛酚和铁氰化物希尔反应的出现。然而，从变绿2小时起就观察到甲基紫精（MV）和烟酰胺腺嘌呤二核苷酸磷酸（NADP）的光还原。可变荧光是水裂解功能的直接指标，从变绿2小时起在子叶、类囊体膜和光系统II（PSII）颗粒中就观察到了。在变绿早期观察到，在MV存在下可变荧光的降低（由于Q-的快速再氧化）证实了PSII对MV的光还原。通过热处理消除类囊体膜和PSII颗粒中的可变荧光，以及在热处理的叶绿体中存在MV时伴随的光依赖氧摄取的丧失，进一步证实了水裂解功能的早期发育。然而，直到变绿8小时，MV和NADP的光还原对系统间电子传递抑制剂二氯苯基二甲基脲或二溴甲基异丙基对苯醌不敏感。尽管从变绿早期就观察到系统间电子载体细胞色素f的氧化，但直到变绿8小时才观察到细胞色素f的还原。所有这些观察结果证实，在变绿早期，MV和NADP由PSII光还原，而不涉及系统间电子载体或PSI的协作。由于这些观察结果与目前普遍流行的光合还原力产生的概念（Z-方案）不一致，该概念需要两个光系统的明确协作，因此提出了一条替代的电子流动途径。
