Photochemical damage and comparative performance of superoxide dismutase and ascorbate peroxidase in sugarcane leaves exposed to paraquat-induced oxidative stress

Autor: Chagas, Roberta M.1, Silveira, Joaquim A.G.2, Ribeiro, Rafael V.3, Vitorello, Victor A.4, Carrer, Helaine1 hecarrer@esalq.usp.br
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Zdroj: Pesticide Biochemistry & Physiology. Mar2008, Vol. 90 Issue 3, p181-188. 8p.
Abstrakt: Abstract: The physiological responses of sugarcane (Saccharum officinarum L.) to oxidative stress induced by methyl viologen (paraquat) were examined with respect to photochemical activity, chlorophyll content, lipid peroxidation and superoxide dismutase (SOD) and ascorbate peroxidase (APX) activities. Thirty-day-old sugarcane plants were sprayed with 0, 2, 4, 6 and 8mM methyl viologen (MV). Chlorophyll fluorescence was measured after 18h and biochemical analyses were performed after 24 and 48h. Concentrations of MV above 2mM caused significant damage to photosystem II (PSII) activity. Potential and effective quantum efficiency of PSII and apparent electron transport rate were greatly reduced or practically abolished. Both chlorophyll and soluble protein contents steadily decreased with MV concentrations above 2mM after 24h of exposure, which became more pronounced after 48h, achieving a 3-fold decrease. Insoluble protein contents were little affected by MV. Oxidative stress induced by MV was evidenced by increases in lipid peroxidation. Specific activity of SOD increased, even after 48h of exposure to the highest concentrations of MV, but total activity on a fresh weight basis did not change significantly. Nondenaturing PAGE assayed with H2O2 and KCN showed that treatment with MV did not change Cu/Zn-SOD and Mn-SOD isoform activities. In contrast, APX specific activity increased at 2mM MV but then dropped at higher doses. Oxidative damage induced by MV was inversely related to APX activity. It is suggested that the major MV-induced oxidative damages in sugarcane leaves were related to excess H2O2, probably in chloroplasts, caused by an imbalance between SOD and APX activities, in which APX was a limiting step. Reduced photochemical activity allowed the early detection of the ensuing oxidative stress. [Copyright &y& Elsevier]
Databáze: GreenFILE
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