Effect of Selenium On Leaf Senescence of Sorghum Grown Under High Temperature Stress.

Selenium (Se) is an essential element for plants and animals. It is a component of the enzyme glutathione peroxidase with an antioxidant activity capable of scavenging reactive oxygen species (ROS). Se has been shown to exert a positive effect on crop growth and stress tolerance at low concentrations. Heat stress can induce changes in photosynthesis, respiration and membrane stability. During heat stress ROS molecules are produced and scavenging of ROS can avoid cellular damage. The objective of this study was to determine if foliar application of selenium is able to retard the high temperature induced oxidative stress in sorghum through its antioxidative functions, and influence leaf senescence, seed yield and components of yield.  A pot experiment was carried out with sorghum (Sorghum bicolor) plants. The plants were grown in glass house (daytime maximum/nighttime minimum 32/22°C) till seed-set and thereafter all plants were transferred to growth chambers and exposed to either optimum temperature (OT, 32/22°C) or high temperature (HT, 40/30°C).  Selenium (sodium selenate) was sprayed at a concentration of 75 ppm before transferring the plants to growth chambers and start of stress treatment. The high temperature stress decreased the chlorophyll content (SPAD value), and increased ROS production and thylakoid membrane damage. When compared to control, Se application increased photosynthetic rate, stomatal conductance and PS II photochemistry under heat stress. Application of Se also decreased levels of ROS (O₂^- and H₂O₂) and thiobarbituric acid reactive substances (TBARS) and leaf senescence, leading to increased yield. These results suggest benefits of selenium application on sorghum physiology and yield under high temperature stress.