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Abha Upadhyaya, Tim D. Davis, and Narendra Sankhla

Moth bean (Vigna aconitifolia Jacqu. Marecbal cv. Jaadia) seeds were germinated in 0, 0.1, 1, or 2 μm EBL. After 72 hours, seedlings were exposed to 22 or 48C for 90 minutes. At 48C, EBL increased total electrolyte, K+, and sugar leakage from the seedlings relative to the control. Following exposure to 48C, EBGtreated seedlings bad higher malondialdebyde concentrations than controls, indicating that EBL enhanced high-temperature-induced lipid peroxidation. At 48C, EBL increased ascorbic acid oxidase activity but decreased superoxide dismutase activity relative to the control. Taken collectively, these data do not support a hypothesis that brassinosteroids confer beat shock tolerance to moth bean. Chemical name used: 24-epibrassinolide (EBL).

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Abha Upadhyaya, Tim D. Davis, and Narendra Sankhla

Seeds of moth bean (Vigna aconitifolia Jacqu. Marechal cv. Jaadia) were germinated in the presence of 0, 0.1, 1, or 2 μm 24-epibrassinolide (EBL). After 72 h, cotyledons were excised and the seedlings exposed to 22 or 48 °C for 90 min. At 48 °C EBL increased total electrolyte, K+, and sugar leakage relative to the untreated control. Following exposure to 48 °C, EBL-treated seedlings had higher malondialdehyde concentrations than controls indicating that EBL enhanced high temperature-induced lipid peroxidation. At 48 °C, EBL increased ascorbic acid oxidase activity and decreased superoxide dismutase activity relative to the control. Taken together, these data do not support the hypothesis that brassinosteroids confer thermotolerance to plants. On the contrary, EBL increased high temperature-induced damage and reduced the activity of some antioxidant systems that may protect against stress-induced cellular damage.

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Donald T. Krizek, Abha Upadhyaya, and Roman M. Mirecki

UV-B (UV) induced changes in PAL activity and UV-absorbing compounds were followed in cotton after 1 to 9 days and in cucumber after 1 to 14 days. UV increased PAL activity in the lower hypocotyl (LH) of cotton but had no effect on the upper portion. In general, PAL decreased with time, but UV treatment slowed that decline in the LH portion. Anthocyanin concentration declined with time in both portions. In cucumber cotyledons, UV had no effect on PAL. In cucumber leaves, there was no overall effect of UV; but there were significant interactions with time. In both cotyledons and in leaves, PAL decreased with time. As in LH cotton tissue, UV slowed the rate of decline of PAL in cucumber leaves. In leaves, UV absorbing compounds (at 330 nm) were increased by UV; in cotyledons, the increase in absorption was greater in controls than in UV-B irradiated seedlings. In cotton, changes in anthocyanins mirrored those in PAL, this was not the case for UV absorbing compounds in either species.