The objective of this review was to integrate the mechanisms by which plants respond to high temperature stress along the soil-plant-atmosphere continuum, from an agronomic perspective. The review presents the physiological basis underlying thermal stress, for which the optimum and threshold temperatures of crops are examined, along with methodologies for its study and the molecular, biochemical and physiological responses of plants to high temperature. The effects of high temperatures on cell ultrastructure and metabolism, respiration, the acclimation of Q10, membrane stability, accumulation of compatible osmolites, production of pigments, secondary metabolites and stress proteins, production of reactive oxygen species (ROS) and antioxidant enzymes, and the effects on photosynthesis and assimilate partitioning are examined. Hormonal changes and signaling regulating plant responses in the field, and the acclimation to temperature stress are also discussed. 

Keywords: antioxidant enzymes, compatible osmolites, heat shock proteins, induced thermo-tolerance.