In the present era of climate change and global warming, high temperatures have increased considerably, posing a threat to plant life. Heat stress affects the biochemistry, physiology and molecular makeup of the plant by altering the key processes, i.e., photosynthesis, respiration and reproduction which reduces its growth and development. There is a dire need to manage this problem sustainably for plant conservation as well as the food security of the human population. Use of phytohormones to induce thermotolerance in plants can be a sustainable way to fight the adversities of heat stress. Phytohormone-induced thermotolerance proves to be a compelling approach to sustainably relieve the damaging effects of heat stress on plants. Salicylic acid (SA) is an essential molecule in biotic and abiotic defense response signal transduction pathways. When supplied externally, it imparts heat stress tolerance to the plants by different means, viz., increased Heat Shock Proteins (HSP) production, Reactive oxygen species (ROS) scavenging, protection of the reproductive system and enhancing photosynthetic efficiency. The effect of SA on plants is highly dependent on the concentration applied, plant species, plant age, type of tissues treated, and duration of the treatment. The present review paper summarizes the mechanism of thermotolerance induced by salicylic acid in plants under heat stress conditions. It includes the regulatory effects of SA on heat shock proteins, antioxidant metabolism, and maintenance of Ca 2+ homeostasis under heat stress. This review combines the studies conducted to elucidate the role of SA in the modulation of different mechanisms which lead to heat stress tolerance in plants. It discusses the mechanism of SA in protecting the photosynthetic machinery and reproductive system during high-temperature stress.

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Salicylic acid (SA) increases crop's resistance against drought stress (DS). The present study reports the effect of SA foliar spray on yield and its components in foxtail millet Basten cultivar under drought stress conditions with three irrigation levels (45%, 65%, and 85% humidity of field capacity) as the main factor and four SA levels (0 to 2 mM) as the subplot. The results revealed that the freshest forage yield (36.76 ton.ha -1 ) and plant height (89.6 cm) is obtained from control and three mM SAFS treatments. The highest stem yield (6.971 ton/ha), leaf yield (4.947 ton/ha), grain yield (2.568 ton/ha), panicle length (18.7 cm), seed number per panicle (3670), 1000-seed weight (3.64 g) and a number of leaves per plant (11.43) were obtained by foliar spraying of 1.0 mM SA under normal conditions. Maximum harvest index (61.66%) was obtained under moderate stress conditions and 1.0 mM SA foliar spray. The highest levels of chlorophyll a, b, and total chlorophyll were 6.35, 4.02, and GUO et al. / Turk J Agric For 382 10.37 mg/WW, respectively, from the treatment without drought stress and the application of 1.0 mM SA. The results showed that spraying 1.0 and 3 mM SA under stress and normal conditions effectively yields and components in foxtail millet Basten cultivar in Sistan weather conditions.