Temperature stress and redox homeostasis in agricultural crops

Plants are exposed to a wide range of environmental conditions and one of the major forces that shape the structure and function of plants are temperature stresses, which include low and high temperature stresses and considered as major abiotic stresses for crop plants. Due to global climate change, temperature stress is becoming the major area of concern for the researchers worldwide. The reactions of plants to these stresses are complex and have devastating effects on plant metabolism, disrupting cellular homeostasis and uncoupling major physiological and biochemical processes. Temperature stresses disrupt photosynthesis and increase photorespiration thereby altering the normal homeostasis of plant cells. The constancy of temperature, among different metabolic equilibria present in plant cells, depends to a certain extent on a homeostatically regulated ratio of redox components, which are present virtually in all plant cells. Several pathways, which are present in plant cells, enable correct equilibrium of the plant cellular redox state and balance fluctuations in plant cells caused by changes in environment due to stressful conditions. In temperature stresses, high temperature stress is considered to be one of the major abiotic stresses for restricting crop production worldwide. The responses of plants to heat stress vary with extent of temperature increase, its duration and the type of plant. On other hand, low temperature as major environmental factor often affects plant growth and crop productivity and leads to substantial crop loses. A direct result of stress-induced cellular changes is overproduction of reactive oxygen species (ROS) in plants which are produced in such a way that they are confined to a small area and also in specific pattern in biological responses. ROS (superoxide; O - 2 , hydroxyl radicals; OH -, alkoxyl radicals and non-radicals like hydrogen peroxide; H 2 O 2 and singlet oxygen; 1 O 2 ) are highly reactive and toxic and cause damage to proteins, lipids, carbohydrates which ultimately results in oxidative stress. ROS may also serve as signaling molecules in mediating important signal transduction pathways that coordinate an astonishing range of diverse plant processes under temperature stress. To counter temperature induced oxidative stress, plants upregulate a variety of enzymatic and non-enzymatic antioxidants which are also information-rich redox buffers and important components of redox signaling that interact with biomembrane-related compartments. They provide essential information on cellular redox state, and regulate gene expression associated with stress responses to optimize defense and survival, stress acclimation and tolerance. The work done by various researchers has explored a direct link between ROS scavenging and plant tolerance under temperature extremes in various crops which include legumes, cereals, oil crops and vegetables. There is ample need to develop temperature tolerance in crop plants by exploring suitable strategies to manage oxidative stress and maintain cellular redox state. Here, we summarize the studies linking ROS and temperature stress in plants, their generation and site of production, role of ROS as messengers as well as inducers of oxidative damage and strategies for the development of temperature stress tolerance involving redox homeostasis in various agricultural crops.