Studies On Active Oxyen, Photosynthesis And Cell Ultrastructure Of Sweet Potato Under The Stress Of Sweet Potato Scab (Sphaceloma Batatas Sawada)

Though field experiments, two sweet potato varietices with different responses to sweet potato scab stress(guangshu88-70-disease resistant; qingshan1255-disease sensitive) were used as experimental materials to study the physiological and biochemical bases of disease tolerance, including metabolism of active oxygen, membrane-lipid peroxidation, metabolism of photosynthesis and the change of ultrastructure.Under sweet potato scab stress, the activities of superpoxide dismutase(SOD), catalase(CAT), and ascorbate peroxidase(ASP) decreased in different degree in both two varietices ; but the peroxidase(POD) increased at both varietices, especial at disease sensitive. The contents of protective materials ascorbic acid(ASA), glutathione(GSH), and carotenoid(CAR) decreased too. Then, on one hand, the contents of hydrogen peroxide(H2O2) and superoxide anion radical(O2- ) accumulated, which increased the permeability and the lipid peroxidetion of the plasma membrance and promotted the accumulation of malonadehyde(MDA).On the other hand, the contents of unsaturation of membrane fatty acids ,the index of the unsatarated fatty acids(IUFA), the membrane fluidity of chloroplast and the activities of Mg+-ATPase and Ca+-ATPase of chloroplast decreased.As to photosynthesis, under disease stress. chlorophyll(CHL) and carotenoid(CAR) decomposed. The stomatal conductance(Gs) ,net photosynthetic rate(Pn) and transpiration rate (Tr) decreased at different degree. But intercellular CO2 concentration(Ci) of sensitive varitices increased at a little degree ane that of resistant varitices didn't change.Under sweet potato scab stress, the ultrastructure changed in both varitices. And the most sensitive organization was cell membrane. The main places that free radical came from-mitochondrion and chloroplast were decomposed at different rate. There were lots of phagosome in sensitive varitices and lots of transitional vesicle in resistant varitices. The transitional vesicle were closed related to repair-deficiency of cell membrane.