Abstract
High temperature (HT) stress is a major environmental stress that limits plant growth, metabolism, and productivity worldwide. Plant growth and development involve numerous biochemical reactions that are sensitive to temperature. Plant responses to HT vary with the degree and duration of HT and the plant type. HT is now a major concern for crop production and approaches for sustaining high yields of crop plants under HT stress are important agricultural goals. Plants possess a number of adaptive, avoidance, or acclimation mechanisms to cope with HT situations. In addition, major tolerance mechanisms that employ ion transporters, proteins, osmoprotectants, antioxidants, and other factors involved in signaling cascades and transcriptional control are activated to offset stress-induced biochemical and physiological alterations. Plant survival under HT stress depends on the ability to perceive the HT stimulus, generate and transmit the signal, and initiate appropriate physiological and biochemical changes. HT-induced gene expression and metabolite synthesis also substantially improve tolerance. The physiological and biochemical responses to heat stress are active research areas, and the molecular approaches are being adopted for developing HT tolerance in plants. This article reviews the recent findings on responses, adaptation, and tolerance to HT at the cellular, organellar, and whole plant levels and describes various approaches being taken to enhance thermotolerance in plants.
Highlights
Among the ever-changing components of the environment, the constantly rising ambient temperature is considered one of the most detrimental stresses
We review the roles of exogenous protectants, the underlying mechanisms for transduction of High temperature (HT) stress signals, and transgenic approaches currently being taken to promote HT stress tolerance in plants
At extreme heat stress plants can show programmed cell death in specific cells or tissues may occur within minutes or even seconds due to denaturation or aggregation of proteins, on the other hand moderately HTs for extended period cause gradual death; both types of injuries or death can lead to the shedding of leaves, abortion of flower and fruit, or even death of the entire plant [14,24]
Summary
Among the ever-changing components of the environment, the constantly rising ambient temperature is considered one of the most detrimental stresses. Heat stress causes alterations in expression of genes involved in direct protection from HT stress [9,10] These include genes responsible for the expression of osmoprotectants, detoxifying enzymes, transporters, and regulatory proteins [11,12]. In conditions such as HT, modification of physiological and biochemical processes by gene expression changes gradually leads to the development of heat tolerance in the form of acclimation, or in the ideal case, to adaptation [13,14]. We review the roles of exogenous protectants, the underlying mechanisms for transduction of HT stress signals, and transgenic approaches currently being taken to promote HT stress tolerance in plants
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