Study On Physiological And Biochemical Characteristics In A Mangrove Plant Rhizophora Stylosa Under Zinc And Cuprum Stress

This study was carried out to investigate the effect of zinc and cuprum on the accumulation, chlorophyll content, antioxidant enzymes and protein expression in a mangrove plant Rhizophora stylosa. The similarities and differences of Zn,Cu effects on Rhizophora stylosa are also discussed. The major resultes are summerized as follows:1. The accumulation of Zn,Cu in R.. stylosa increased as the concentration treatment was enhanced. Zn,Cu in R.. stylosa leaves were different. Zn content increased as the treatment level enhanced while Cu content firt increased and then decreased.2. Chlorophyll a, b, total chlorophyll experienced increment in lower concentrations of Zn,Cu (0.2 and 1 mmol·L-1)and value of chlorophyll a/b decreased than the controls suggesting chlorophyll b was stimulated. In higher concentrations(10 and 20 mmol·L-1)the chlorophyll a, b, total chlorophyll declined and the value of chlorophyll a/b increased than the controls indicating that the destruction of Cu and Zn to chlorophyll b was stronger than to a.Both Zn,Cu induced membrane lipid peroxidation in R.. stylosa seedlings. The extent of lipid peroxidation caused by these two heavy metals was equivalent.3. The effects of Zn,Cu on POD and SOD activities in root and leaf extracts of R.. stylosa seedlings were similar. The POD activites were stimulated in lower metal ion concentrations (0.2 mmol·L-1for roots and 0.2,1,5 and 10 mmol·L-1 for leaves) but were inhibited in higher concentrations (1,5,10 and 20 mmol·L-1for roots and 20 mmol·L-1for leaves). The effects of Zn,Cu on root SOD activities were similar. The SOD activities in roots increased when low metal concentration treated and declined when high concentration treated. SOD activities in leaves increased as the Zn concentration was enhanced while the activities first increased and then decreased under Cu treatment. The CAT activities were stimulated under 0.2,1 and 5 mmol·L-1 Zn and were inhibited by 20 mmol·L-1Zn while they were significantly inhibited when 10 mmol·L-1Cu supplied.4. The effects of Zn,Cu on the isoform of antioxidant enzymes in root and leaf in seedlings were analyzed by means of PAGE. The effects of Zn,Cu on the expression of POD isoenzyme in root and leaf extracts of seedlings were similar. The activity of leaf SOD LS-1 increased when low metal treated but decreased but the high concentrations were applied. LS-1 was significantly inhibited by 5 mmol·L-1Cu. It was indicated that low Zn,Cu increased the CAT activities in root and leaf but high concentration especially the Cu decreased the CAT activities.5. The effects of Zn,Cu on the protein expression in the leaves of seedlings were investigaed by means of SDS-PAGE. It is found that 1,5,10 and 20 mmol·L-1 Zn and 0.2,1 and 5mmol·L-1 Cu increased the protein content, and then 5,10mmol·L-1 Cu decreased. The expression of 97,21 and 19 kDa protein increased, Under 10 and 20 mmol·L-1 Zn,Cu treatment, the expression of 45 kDa and 14 kDa protein decreased suggesting that these proteins were closely related to the tolerance of R.. stylosa seedlings under Zn,Cu stress.