Manganese and Oxidative Damage in Cucumber

ABSTRACT

Micronutrients in low or high concentration can affect growth, respiration, photosynthesis, and reproduction in plants. Cucumber (Cucumis sativus, L.) is grown in India in areas low or high in manganese concentration in soils. A study was conducted to investigate the effects of manganese concentration on some metabolic activities affecting developmental responses in cucumber. Seed of cucumber, cv. Sonali, were grown in refined sand and provided manganese at rates of: 0.1, 1.0, 2.0, 10, 100, or 200 μM on 6 of 7 days in a week for up to 102 days. At 20 days after planting, symptoms of leaf interveinal chlorosis, which intensified later and developed into irregular brown spots, developed with daily application rates of <10 μM Mn. When daily application of >10 μM of Mn was used interveinal chlorosis on old leaves was followed by necrosis and death of the leaf lamina. Plant growth was retarded. Plants treated with Mn above or below 10 μM had lower fruit yield and lower biomass, concentrations of chlorophylls (a and b), Hill reaction activity, and catalase activity than those grown with 10 μM. There was increased activity of peroxidase, superoxide dismutase, and ascorbate peroxidase in plants treated with Mn above or below 10 μM. The Mn concentration in tissues increased as levels of Mn increased from 0.1 to 200 μM. Detrimental effects due to manganese <10 and >10 μM was related to the Mn concentration in the leaves.

KEYWORDS:

• Cucumis sativus
• oxidative stress
• reactive oxygen species
• Hill reaction activity