Understanding Heat Stress and Tolerance Mechanisms in Wheat (Triticum aestivum L.): A Comprehensive Review

Wheat (Triticum aestivum L.), a vital cereal crop in the Poaceae family, plays a crucial role in global agriculture. It contributes approximately 30% of the world's grain production and constitutes half of the grain traded internationally. Serving as a staple food in over 40 countries, wheat provides essential calories to 85% of the global population and protein to 82%. With the global population expected to reach 9.1 billion by 2050, the Food and Agriculture Organization (FAO) projects that nearly one billion additional tons of cereal will be needed annually to meet increasing demand. Enhancing wheat productivity and production is thus essential. Wheat is cultivated in tropical and subtropical regions, where it faces various abiotic stresses that significantly impact yield, with heat and drought being the most critical challenges. Global climate models predict a potential increase in mean ambient temperature by up to 6°C by the end of the century. Wheat is highly sensitive to heat stress; even a 1°C rise in temperature can reduce global wheat production by 6%. Heat stress affects wheat's physiological, biological, and biochemical processes, including seed germination, grain filling duration, grain number, Rubisco enzyme activity, photosynthetic capacity, assimilate translocation rate, leaf senescence, chlorophyll content, and overall yield. To combat heat stress, wheat has developed diverse tolerance mechanisms. These include the induction of heat shock proteins (HSPs) that assist in proper protein folding and the activation of an antioxidative defense system to detoxify reactive oxygen species (ROS). Traits like Stay Green (SG), chlorophyll fluorescence, and canopy temperature are closely linked to heat tolerance. Understanding and improving these mechanisms are imperative to sustain and enhance wheat production to meet future food demands amidst global climate changes. This review provides a comprehensive analysis of the effects of heat stress on wheat morphology, physiology, and biochemistry. It also discusses the mechanisms of heat tolerance, emphasizing the importance of developing crop varieties capable of withstanding future climatic conditions. Understanding these mechanisms at physiological, biochemical, and morphological levels is crucial for ensuring future food security.