Chickpea is a heat sensitive crop hence its potential yield is considerably reduced under high temperatures exceeding 35°C. In the present study, we evaluated the efficacy of proline in countering the damage caused by heat stress to growth and to enzymes of carbon and antioxidative metabolism in chickpea. The chickpea seeds were raised without (control) and with proline (10 μM) at temperatures of 30/25°C, 35/30°C, 40/35°C and 45/40°C as day/ night (12 h/12 h) in a growth chamber. The shoot and root length at 40/35°C decreased by 46 and 37 %, respectively over control while at 45/40°C, a decrease of 63 and 47 %, respectively over control was observed. In the plants growing in the presence of 10 μM proline at 40/35°C and 45/40°C, the shoot length showed improvement of 32 and 53 %, respectively over untreated plants, while the root growth was improved by 22 and 26 %, respectively. The stress injury (as membrane damage) increased with elevation of temperatures while cellular respiration, chlorophyll content and relative leaf water content reduced as the temperature increased to 45/40°C. The endogenous proline was elevated to 46 μmol g −1 dw at 40/35°C but declined to 19 μmol g −1 dw in plants growing at 45/40°C that was associated with considerable inhibition of growth at this temperature. The oxidative damage measured as malondialdehyde and hydrogen peroxide content increased manifolds in heat stressed plants coupled with inhibition in the activities of enzymatic (superoxide dismutase, catalase, ascorbate peroxidase, glutathione reductase) and levels of non-enzymatic (ascorbic acid, glutathione, proline) antioxidants. The enzymes associated with carbon fixation (RUBISCO), sucrose synthesis (sucrose phosphate synthase) and sucrose hydrolysis (invertase) were strongly inhibited at 45/40°C. The plants growing in the presence of proline accumulated proline up to 63 μmol g −1 dw and showed less injury to membranes, had improved content of chlorophyll and water, especially at 45/40°C. Additionally, the oxidative injury was significantly reduced coupled with elevated levels of enzymatic and non-enzymatic antioxidants. A significant improvement was also noticed in the activities of enzymes of carbon metabolism in proline-treated plants. We report here that proline imparts partial heat tolerance to chickpea's growth by reducing the cellular injury and protection of some vital enzymes related to carbon and oxidative metabolism and exogenous application of proline appears to have a countering effect against elevated high temperatures on chickpea.

The rising temperatures ([35°C) are proving detrimental to summer-sown mungbean genotypes that experience inhibition of vegetative and reproductive growth. In the present study, the mungbean plants growing hydroponically at varying temperatures of 30/20°C (control), 35/25, 40/30, and 45/35°C (as day/night 12 h/12 h) with (50 lM) or without ascorbic acid (ASC) were investigated for effects on growth, membrane damage, chlorophyll loss, leaf water status, components of oxidative stress, and antioxidants. The ASC-treated plants showed significant improvement in germination and seedling growth especially at 40/30 and 45/35°C. The damage to membranes, loss of water, decrease in cellular respiration, and chlorophyll were significantly prevented by ASC treatment to plants growing at these temperatures. The oxidative stress measured as malondialdehyde and hydrogen peroxide content was observed to be significantly lower at high temperatures with ASC application. The activities of superoxide dismutase, catalase, ascorbate peroxidase, and glutathione reductase increased at 40/30°C but decreased at 45/35°C in the absence of ASC while with its application, the activities of these enzymes were appreciably resorted. Among all the antioxidants, the endogenous ASC content decreased to the greatest extent at 45/35°C grown plants indicating its vital role in affecting the response of mungbean to heat stress. Exogenously applied ASC raised its endogenous content along with that of glutathione and proline at 45/35°C. The findings indicated that heat stress-induced inhibition in growth and chlorosis was associated with decrease in leaf water status and elevation of oxidative stress, which could partly be prevented by exogenous application of ASC. Its role in imparting protection against heat stress is discussed.

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Bean (Phaseolus vulgaris L.) seedlings were subjected to varying selenium levels (1, 2, 4, and 6 ppm) in a hydroponic culture. The germination reached 100% in 48 h in all Se levels except 6 ppm, where it took 72 h. The root and shoot growth was stimulated at 1 and 2 ppm Se levels that was commensurate with increase in chlorophyll content, leaf water content, and cellular respiration. At 4 and 6 ppm Se levels, the growth was inhibited appreciably, which was associated with increase in stress injury measured as damage to membranes and decrease in cellular respiration, chlorophyll, and leaf water content. The oxidative injury as elevation of lipid peroxidation was larger compared to hydrogen peroxide accompanied by reduced levels of enzymatic (superoxide dismutase, catalase, ascorbate peroxidase, and glutathione reductase) and non-enzymatic (ascorbic acid and glutathione) antioxidants. Proline content was significantly higher at 1 and 2 ppm Se but diminished considerably at 4 and 6 ppm levels concomitant with the reduced growth. Exogenous application of proline (50 µM) resulted in substantiation of its endogenous levels that antagonised the toxic effects of Se by improving the growth of seedlings. The stress injury was reduced significantly with simultaneous increase in enzymatic and non-enzymatic antioxidants. Especially the components of ascorbate-glutathione cycle showed larger stimulation with proline application. The role of proline in mitigating the toxic effects of Se is discussed.

The mungbean plants were grown hydroponically in the absence (control) or presence of 0.1, 0.25, 0.50 and 0.75 ppm selenium (as sodium selenate) for 10 days. The growth of shoots and roots increased with application of selenium with greater extent in shoots. With 0.5 and 0.75 ppm Se levels, the shoot growth was stimulated by 24% to 27% over control, respectively, while the roots showed a corresponding increase of 18-19%, respectively. The shoot-to-root ratio was enhanced significantly with Se application and maximum effects occurred at 0.75 ppm Se. A significant increase was observed in chlorophyll and cellular respiration ability with 0.5 and 0.75 ppm selenium. The increase in growth by selenium was accompanied by elevation of starch, sucrose and reducing sugars. The activity of starch hydrolysing enzymes--amylases and sucrose hydrolysing enzyme--invertase was stimulated significantly with selenium. This was associated with elevation of activities of sucrose synthesising enzymes--sucrose synthase and sucrose phosphate synthase. It was concluded that increase in growth of shoots and roots by application of Se was possibly the result of up-regulation of enzymes of carbohydrate metabolism thus providing energy substrates for enhanced growth.

Among various abiotic stresses, heat stress is one of the most damaging, threatening plant productivity and survival all over the world. Warmer temperatures due to climatic anomalies above optimum growing temperatures have detrimental impacts on crop yield potential as well as plant distribution patterns. Heat stress affects overall plant metabolism in terms of physiology, biochemistry, and gene expression. Membrane damage, protein degradation, enzyme inactivation, and the accumulation of reactive oxygen species are some of the harmful effects of heat stress that cause injury to various cellular compartments. Although plants are equipped with various defense strategies to counteract these adversities, their defensive means are not sufficient to defend against the ever-rising temperatures. Hence, substantial yield losses have been observed in all crop species under heat stress. Here, we describe the involvement of various plant growth-regulators (PGRs) (hormones, polyamines, osmoprotectants, antioxidants, and other signaling molecules) in thermotolerance, through diverse cellular mechanisms that protect cells under heat stress. Several studies involving the exogenous application of PGRs to heat-stressed plants have demonstrated their role in imparting tolerance, suggesting the strong potential of these molecules in improving the performance of food crops grown under high temperature.