Light and Excess Manganese

Abstract

The effect of light intensity on antioxidants, antioxidant enzymes, and chlorophyll content was studied in common bean (Phaseolus vulgaris L.) exposed to excess Mn. Leaves of bean genotypes contrasting in Mn tolerance were exposed to two different light intensities and to excess Mn; light was controlled by shading a leaflet with filter paper. After 5 d of Mn treatment ascorbate was depleted by 45% in leaves of the Mn-sensitive genotype ZPV-292 and by 20% in the Mn-tolerant genotype CALIMA. Nonprotein sulfhydryl groups and glutathione reductase were not affected by Mn or light treatment. Ten days of Mn-toxicity stress increased leaf ascorbate peroxidase activity of cv ZPV-292 by 78% in low light and by 235% in high light, and superoxide dismutase activity followed a similar trend. Increases of ascorbate peroxidase and superoxide dismutase activity observed in cv CALIMA were lower than those observed in the susceptible cv ZPV-292. The cv CALIMA had less ascorbate oxidation under excess Mn-toxicity stress. Depletion of ascorbate occurred before the onset of chlorosis in Mn-stressed plants, especially in cv ZPV-292. Lipid peroxidation was not detected in floating leaf discs of mature leaves exposed to excess Mn. Our results suggest that Mn toxicity may be mediated by oxidative stress, and that the tolerant genotype may maintain higher ascorbate levels under stress than the sensitive genotype.

Enhanced sensitivity to oxidative stress in transgenic tobacco plants with decreased glutathione reductase activity leads to a decrease in ascorbate pool and ascorbate redox state

“…Ascorbate peroxidase (APX, EC1.11.1.11) activity was determined by monitoring the decrease in absorbance at 290 nm due to ascorbate oxidation (González et al 1998). Dehydroascorbate reductase (DHAR, EC1.8.5.1) activity was determined by the increase in absorbance at 295 nm due to DHA reduction (Knörzer et al 1996).…”

“…Enzyme measurements GR activity was determined by following the rate of GSH formation at 412 nm (González et al 1998). Ascorbate peroxidase (APX, EC1.11.1.11) activity was determined by monitoring the decrease in absorbance at 290 nm due to ascorbate oxidation (González et al 1998).…”

Heavy metal toxicity in rice and soybean plants cultivated in contaminated soil

“…According to Gonzalez et al (1998), temperatures above 30°C reduce the toxicity intensity and effect of manganese.…”

Antioxidative protection and proteolytic activity in tolerant and sensitive wheat (Triticum aestivum L.) varieties subjected to long-term field drought

“…The gels were loaded with extract volume equivalent to 2 mg leaf FW. After electrophoresis SOD activity in gels were visualized according to González et al (1998). SOD types were differentiated by pre-stain incubation for 30 min in 50 mM potassium phosphate buffer, pH 7.8 containing 5 mM H 2 O 2 or 3 mM KCN.…”