Physiological and biochemical responses to high light and temperature stress in plants

Light intensity and temperature are primary environmental factors affecting the growth and development of plants. Changes in their intensity, range and duration can lead to acclimatory responses, cellular damage and ultimately to the death of plants. Plants have evolved several efficient protective mechanisms that make it possible for them to survive under unfavorable light and temperature conditions. These mechanisms are linked predominantly to the photosynthetic electron transport chain, xanthophyll cycle and the photorespiratory pathway. Under stress conditions, elevated levels of reactive oxygen species (ROS) are produced, which in addition to deleterious effects also show signalling functions. In response to enhanced ROS formation, different low-molecular antioxidants are synthesized, as well as antioxidant enzymes. Depending on the stress intensity and its duration, the content of synthesized antioxidants varies. Under severe, short light/temperature stress, the contents of low-molecular weight antioxidants, such as ascorbate, glutathione and prenyllipids, tend to decrease, which is correlated with an extra need for ROS scavenging. Under longer exposure of plants to unfavorable light and temperature conditions, the contents of antioxidants gradually increase as a result of acclimation during long-term responses. Studies on plant antioxidant responses indicate that a crucial part of the antioxidant network operates in chloroplasts and their action shows a high level of interdependence. The antioxidant response also depends on plant stress-tolerance, and frequently varies for different species. Therefore studying a wide range of plant species is a fruitful approach to investigating the natural variation in the antioxidant response of plants in relation to excess light and temperature.