LIMITATION OF ELECTRON-TRANSPORT TO NADP ON THE SECTOR OF PHOTOSYSTEM-I DURING SENESCENCE OF BARLEY LEAVES

We studied electron transport in the complete noncyclic chain with phy siological electron acceptors (NADP and molecular oxygen) and in PSII with an artificial electron acceptor (DCPIP), and investigated the con tent of components of the ETC on its terminal sector in barley leaves (Hordeum vulgare L.) of different ages. The rate of electron transport on different sectors of the chain declined unequally in the process o f leaf senescence. Decrease in the number of PSI reaction centers is o ne of the factors behind the sharp decline of electron flow on the sec tor of PSI as compared with PSI. On the other hand, the more pronounce d decline of electron transport to NADP rather than to molecular oxyge n is associated with decrease in the content of ferredoxin and ferredo xin:NADP oxidoreductase, which leads to an increase in efficiency of e lectron transport to molecular oxygen as compared with reduced NADP. I t is hypothesized that exchange of electron transport pathways occurs during leaf senescence.