Influence of selenium on growth and metabolism in rice (Oryza sativa l.) and its possible interaction with sulphate

The effect of selenate (Na₂SeO₄) with or without sulphate (Na₂SO₄) was studied on the growth and metabolism in rice seedlings cv. Khitish and cv. Satabdi. In the test cultivars, selenate at 2M concentration showed growth promoting effects in comparison to 20M selenate and above, where mostly inhibitory effects were observed. The levels of total chlorophyll, chlorophyll a, chlorophyll b, carotene, xanthophyll and intensity of chlorophyll fluorescence were also similarly affected. Selenium has been attributed with a protective role against formation of reactive oxygen species (ROS) in plants subjected to stress. High concentration of selenate induced differential effects in the activities of antioxidant scavenging enzymes, viz., SOD, CPX, AOX and CAT in rice seedlings. Activities of SOD and AOX were decreased, whereas CAT and CPX activities were increased. In these seedlings receiving high concentrations of selenate, the levels of oxidative stress markers, viz., proline, H₂O₂ and MDA were enhanced. Application of sulphate jointly with selenate reversed the inhibitory effects of high concentration of selenate treatment alone on all parameters tested, which ultimately led to enhanced growth and metabolism in rice seedlings. Thus selenium has a dose dependent effect on the physiological and biochemical responses of rice seedlings, with low concentration of selenate inducing a stimulatory effect on growth and metabolism as against high concentration of selenate which proved to be toxic to the rice seedlings.