Photosynthetic Electron Transport in Plastids in Detached Cucumber Cotyledons Treated with 6-Benzylaminopurine and Potassium

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Etiolated cotyledons of cucumber (Cucumis sativus L.) were excised and incubated for 16 days on agar in the absence or in the presence of 6-benzylaminopurine (BA) (3 μM) or KCl (10 mM) under continuous light. Treatment with BA or KCl increased growth and greening of cotyledons, KCl being particularly active during the last few days of the incubation. The rate of photosynthetic electron transport reached a maximum after 3 days, as did the chlorophyll content, and then it declined by approximately 95%. An uncoupling from phosphorylation was observed in older cotyledons. BA and KCl increased the rate of electron flow per cotyledon, and KCl delayed the onset of the decline in this rate. PS I and PS II activities per chlorophyll unit were lower in BA-treated cotyledons, but KCl-treated cotyledons behaved like the controls. Fluorescence analysis indicated that the level of active chlorophylls involved in the transfer of energy in PS II decreased between 3 and 7 days under all conditions tested. In BA-treated cotyledons, the proportion of active chlorophylls was consistently lower than that in the control. Thus, it appears that, in the absence of exogenous K^+, cytokinin has only a low antisenescence effect on photosynthetic activity, and that K^+ may enhance the photosynthetic electron flow between plastoquinone and plastocyanin via the cytochrome b_6-f complex.
日本植物生理学会の論文