Relationship between photosystem stoichiometries and changes in active oxygen scavenging enzymes in natural grown rice seedlings

Abstract

The relationship between antioxidative enzymes and photosystemstoichiometries was examined in rice leaves. The photosystem (PS) II/PS Ireaction centre ratio decreased from the top to the bottom leaves, suggestinganimbalance of light absorption and electron flow as well as a probableover-reduction between the two photosystems. We used rice leaves from juvenileseedlings and obtained the following results: (1) Photosynthetic capacitymeasured from the pulse-amplitude modulation (PAM) fluorometer showed the PS IIphotochemistry to have a reduced capacity, but the excitation-energy trappingcapacity at PS II gradually increased from the top to the bottom leaves. (2)Thelevels of Chl, soluble protein, and ascorbate decreased, but those ofH2O2 increased slightly in the bottom leaves. (3) Whendetermined on the basis of leaf area, glycolate oxidase, catalase, ascorbateperoxidase and glutathione reductase degraded in the bottom leaves. (4) On thebasis of unit of Chl, the levels of superoxide dismutase (SOD) and guaiacolperoxidase (GPX) increased dramatically. Based on the above results, we discussthe relationship between the two photosystem stoichiometries and changes in theantioxidative enzymes.