Abstract
Plants are constantly exposed to various abiotic and biotic stresses in nature. Abiotic stresses such as extreme temperatures (heat, cold, and freezing), salinity, and drought are critical factors that reduce crop yields for most major crops by more than 50% worldwide. The situation may become worse as a result of climate change, which may multiply the frequency and severity of such abiotic stress events. Hence, there is an urgent need to develop improved varieties that are more resilient to abiotic stresses. To survive under stress conditions, plants have evolved intricate mechanisms to perceive external signals, allowing optimal response to environmental conditions. Intensive research over the last decade has gradually unraveled the mechanisms that underlie how plants react to environmental adversity, but many aspects are still subjects of intensive research. Acquired stress tolerance in plants is often a result of various stress‐response mechanisms that act coordinately or synergistically to prevent cellular damage and to reestablish cellular homeostasis. The phenomenon of cross‐tolerance to different stresses, which is triggered by exposure to a single stress, is widespread in plants; however, little is known about the molecular mechanisms underlying cross‐tolerance. Cross‐tolerance is extremely important for agriculture because plants can be selectively bred that are tolerant to more than one stress. Additionally, cross‐tolerance allows us to compare and contrast individual responses and to examine the roles of common signal‐transducing molecules. Prior or simultaneous exposure to one stressor often affects how plants respond to other stresses, indicating extensive overlap and crosstalk between stress‐response signaling pathways. The synergistic coactivation of plant stress responses confers a preemptive advantage by enabling a general increase in stress resistance following exposure to a single stress condition. Numerous studies have shown that reactive oxygen species (especially hydrogen peroxide) and methylglyoxal exhibit important signaling functions and reinforce resistance to abiotic stress by modulating the expression of genes associated with tolerance. Such studies support the concept that there might be common factors controlling cross‐tolerance, at least at the cellular level. Accumulating evidence supports the notion that the plant antioxidant defense system works in harmony with the glyoxalase system, thus providing better defense against abiotic stresses. This chapter summarizes our current understanding of the possible mechanisms associated with heat‐ or cold‐shock‐induced cross‐adaptation to chilling, heat, salt, drought, and heavy metals in plants, with special reference to reactive oxygen species and methylglyoxal metabolisms. We also aim to highlight the roles other key factors have in abiotic stress signaling and their roles in shaping the outcome of cross‐adaptation reactions.