ALTERATION IN PHOTOSYSTEM-II PHOTOCHEMISTRY OF THYLAKOIDS ISOLATED FROM SENESCING LEAVES OF WHEAT SEEDLINGS

Wheat seedlings, grown for 7 days in the light, were allowed to senesc e in the light or dark, and the change in the photosystem II (PS II) p hotochemistry of chloroplasts isolated from the primary leaves of thes e seedlings was investigated. The decrease in oxygen evolution and the fast fluorescence results indicated that the impairment of PS II in t he leaves of seedlings senescing in the light was different from that in the leaves of seedlings senescing in the dark. Thermoluminescence s tudies showed a structural modification in the Q(B) protein of chlorop lasts isolated from leaves senescing in the light and an alteration in the S state transition of chloroplasts isolated from leaves senescing in the dark.