Abstract: The effect of strong light in the presence of methyl viologen (MV) on the contents of souble protein and its free carbonyl, photosynthetic pigments, malondialdehyde (MDA), and ch]orophyil fluorescence parameters were investigated in the leaf discs from plants with different photosyn, thetic pathways. The photooxidafive degradation of soluble protein and ch]orophyll occurred after 1 h of treatment, and was accompanied by the increase of malondialdehyde content, and oxygen uptake in the light and dark, as well as the inactivation of PS Ⅱ in all test plants. Unlike the maize ( Zea mays ) and sugarcane ( Saccharum sinense Roxb. ) ( C4 plant ) or pineapple (Ananas comosus ( L. ) Mere. ) (CAM plant), a marked increase of carotenoid and non-photochemical chlorophyll fluorescence quenching(qN) was observed in peanut ( Arachis hypogaea L. ) leaves ( C3 plant), as the photochemical fluorescence quenching (qp) declined and Fo raised. It is suggested that photooxidafive stress induced the active dissipation of excessive excite energy by antenna quenching in C4 plant. The response of increasing 02 uptake in the dark was also found in C4 plants during photooxidation. However, the extents of protein and lipid destruction were larger in leaves of maize and sugarcane than in peanut leaves. Fo went up significantly as the C3 plant did, but qN dropped down to the lowest value (10% of control), which may regard as an obvious change of photooxidative damage in C4 plants. Among the three types of plants, the CAM plant, pineapple showed stronger antioxidative feature due to the relative small range of changes in the estimated items as compared with the control.

Key words: Photosynthetic pathway, Leaf discs, Photooxidation, Methyl viologen, Chlorophyll fluorescence, Free carbonyl