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

Abstract

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 6(th) d after germination and they declined to 50 and 41%, respectively, by the 20(th) day of growth. Activities of both photosystem (PS) 2 and PS1 decreased by 33 and 31%, respectively, on the 20(th) day, compared to the control 6(th) day. Changes in sensitivity of PS2 to inhibitors like atrazine and dibromothymoquinone and sensitivity of PS1 to KCN accompanied the changes in PS2 and PS1 activities. Hence both the acceptor side of PS2 and the donor side of PS1 are affected by senescence-induced changes in cucumber cotyledonary leaves.