Alterations in electron transport characteristics during senescence of Cucumis cotyledonary leaves. Analysis of the effects of inhibitors

Cotyledonary leaves of Cucumis sativus cv. Poinsette exhibited senescence-induced losses in chlorophyll (Chl) and protein contents within three weeks since germination. Chl and protein concentrations in cotyledonary leaves approached maximum on 6th d after germination and they declined to 50 and 41 %, respectively, by the 20th day of growth. Activities of both photosystem (PS) 2 and PS1 decreased by 33 and 31 %, respectively, on the 20th day, compared to the control 6th day. Changes in sensitivity of PS2 to inhibitors like atrazine and dibromothymoquinone and sensitivity of PS 1 to KCN accompanied the changes in PS2 and PS 1 activities. Hence both the acceptor side of PS2 and the donor side of PSl are affected by senescence-induced changes in cucumber cotyledonary leaves.