Food crops face rising temperatures: An overview of responses, adaptive mechanisms, and approaches to improve heat tolerance

The rising temperatures are resulting in heat stress for various agriculturalcrops to limit their growth, metabolism, and leading to significant loss of yieldpotential worldwide. Heat stress adversely affects normal plant growth and developmentdepending on the sensitivity of each crop species. Each crop species has its ownrange of temperature maxima and minima at different developmental stages beyondwhich all these processes get inhibited. The reproductive stage is on the whole moresensitive to heat stress, resulting in impaired fertilization to cause abortion of flowers.During seed filling, heat stress retards seed growth by affecting all the biochemicalevents to reduce seed size. Unfavorable temperature may significantly affect photosynthesis,respiration, water balance, and membrane stability of leaves. To combatheat stress, plants acquire various defense mechanisms for their survival such asmaintaining membrane stability, and scavenging reactive oxygen species by generatingantioxidants and stress proteins. Thermo-tolerance can be improved by the accumulationof various compounds of low molecular mass known as thermo-protectantsas well as phyto-hormones. Exogenous application of these molecules has benefitedplants growing under heat stress. Alternatively, transgenic plants over-expressingthe enzymes catalyzing the synthesis of these molecules may be raised to increasetheir endogenous levels to improve heat tolerance. In recent times, various transgenicshave been developed with improved thermo-tolerance having potential benefitsfor inducing heat tolerance in food crops. Updated information about of the effectsof heat stress on various food crops and their responses as well as adaptive mechanismsis reviewed here.