Effect of chemical reductant and photosystem II light on the yield of chlorophylla luminescence in isolated chloroplasts

Abstract

Millisecond delayed luminescence (DL), and chlorophylla (Chla) fluorescence of normal and tris-washed chloroplasts were monitored in the presence of agents that bring about reduction ofQ, the photosystem II (PS II) primary acceptor, and Chla fluorescence quencher. The DL intensity becomes low ifQ is chemically reduced in dark, or by photochemical reduction in the presence of the herbicide diuron. Sillicomolybdate which by-passes the diuron block and accepts electrons directly fromQ enhances the DL. Chla fluorescence is enhanced upon dark chemical reduction ofQ by chemical reductant sodium dithionite. A small fraction ofQ still remains inaccessible to dithionite, and which gets reduced by PS II light. Thus theQ pool in the electron transport chain seems to be heterogenous. However, DL intensity changes are dependent upon the redox state of the large fraction ofQ pool.