The changes in photosystem II photochemistry and photosynthetic pigment contents were investigated in marrow leaves during senescence. Through the development of senescence, the efficiency of PSII photochemistry declined slightly under low light condition at early morning and substantially under high light condition at midday. The photochemical quenching expressed significant decrease both in the early morning and at midday. The decrease was more pronounced at midday rather than early morning. The actual efficiency of PSII and photochemical quenching followed the same pattern of the photochemical quenching. Non-photochemical quenching and the content of both antheraxanthin and zeaxanthin increased in the early morning and at midday on the expense of violaxanthin, with remarkable increase at midday. During leaf senescence the content of chlorophyll, b-carotene and neoxanthin decreased, however xanthophy and lutein cycle pigments were slightly affected. This resulted in increases in lutein/chlorophyll and xanthophylls cycle pigments/chlorophyll ratios. Appreciable increase in the ratio of chlorophyll a/b was also observed. Thus, the present results implicate that there was a change in photosynthetic pigment stoichiometry during leaf senescence and that a down-regulation of PSII occurred in senescent leaves when exposed to high light. In addition, the results demonstrate that the xanthophylls cycle-related thermal dissipation in the PSII antenna was enhanced in senescent leaves, which may protect the photosynthetic apparatus from damage by photoinhibition in senescent leaves when exposed to high light. The activities of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), glutamate dehydrogenase (GDH; EC 1.4.1.4) and glucose-6-phosphate dehydrogenase (G-6-P DH; EC. 1.1.1.49) were decreased after induction of senescence.