Physiology of high temperature stress tolerance in vegetables

Crop production is highly sensitive to elevated temperatures. A rise of a few degrees above the optimum growing temperature can lead to a dramatic yield loss. Heat stress influences an array of processes including physiological, growth, developmental, yield, and quality of crop. High temperature may slow down or prevent germination, depending on plant species and stress intensity, and, at later stages, may adversely affect photosynthesis, respiration, water relations and membrane stability. Plant reproduction is the most temperature-sensitive process in the plant life cycle. More precisely, pollen quality is strongly affected by heat stress conditions. High temperature leads to a decrease of pollen viability which is directly correlated with a loss of fruit production. The reduction in pollen viability is associated with changes in the level and composition of several (groups of) metabolites, which play an important role in pollen development, for example by contributing to pollen nutrition or by providing protection to environmental stresses. Metabolic alterations caused by heat stress can lead to severe damage in sensitive plants compared to tolerant plants. In this review, the effects of heat stress on processes by which plants respond, including the contribution of HSP, QTL and metabolomics studies to its understanding and performance of some vegetable crops under high temperature are discussed.