Role of Proline in Mitigating the Deleterious Effects of Heat Stress in Chillies

Chilli is a spicy crop which belongs to family Solanaceae. As a vegetable crop, it is considered as one of the major cultivated crops in the world seriously affected by the climatic changes, including elevation in temperature. Therefore, in this research various morpho-physiological characteristics of chilli were studied for heat tolerance under the influence of exogenous application of proline. This research was carried out in a growth room of the Institute of Horticultural Sciences, University of Agriculture, Faisalabad, Pakistan. Four chilli genotypes were evaluated under the applied conditions. Seeds were grown in plastic pots. Heat stress (40/32 ºC day and night temperature) was applied 30 days after the emergence. Foliar spray of proline (0, 5 and 10 mM) was applied during heat stress, and after 7 days of stress the plants were harvested. The results revealed that the inhibition of chilli growth by heat stress was successfully mediated by proline application. Morphological attributes such as the number of leaves per plant, root and shoot length, plant fresh and dry weight were reduced in response to heat stress, and physiological attributes such as photosynthetic rate, water use efficiency and chlorophyll contents were also reduced in response to heat stress, except transpiration rate and stomatal conductance, which increased under heat stress and showed recovery by proline application. Exogenous application of proline promoted tolerance against heat stress in chilli genotypes and enhanced growth. All the observed traits exhibited recovery in response to proline stimulus, indicating the role of proline in mitigating the consequences of heat stress. Recovery also depends on genetic capability of various cultivars.