Light-induced ascorbate-dependent electron transport and membrane energization in chloroplasts of bundle sheath cells of the C-4 plant maize

Chloroplasts in bundle sheath cells (BSC) of maize perform photosystem I (P SI)-mediated production of ATP. In this study, the participation of ascorba te (Asc) as an electron donor to PST in light-induced electron transport in isolated maize BSC was demonstrated. It was found that Asc, at physiologic al concentrations, rapidly reduced photooxidized reaction center chlorophyl l of PSI (P700), The rate of Asc donation of electrons to P700(+) reached r ates of 50-100 mu equivalents (mg Chi)(-1) h(-1) at 70-80 mM ascorbate with methyl viologen as an electron acceptor, Electron transport supported by A sc was coupled with membrane energization, as demonstrated by the light-ind uced formation of a trans-thylakoid electric field measured by the electroc hromic shift of carotenoids. The possible physiological function of Asc-dep endent electron transport in bundle sheath chloroplasts of maize, as an ele ctron donor for linear electron flow versus sustaining cyclic electron tran sport, is discussed. (C) 2001 Academic Press.