Influence of Selenium on Growth, Antioxidants Production and Physiological Parameters of Rice (&i&Oryza sativa&/i& L.) Seedlings and Its Possible Reversal by Coapplication of Sulphate

摘要

The effect of selenate (Na _( 2 ) SeO _( 4 ) ) and sulphate (Na _( 2 ) SO _( 4 ) ) was studied on growth and metabolism in two rice cultivars cv. satabdi and cv. khitish . Selenate at low concentration (2 μM) expressed growth promoting effect on rice seedlings as opposed to its high concentration (≥20 μM) where the test seedlings showed stunted growth with browning at the apices of both roots and shoots. The chlorophyll contents showed a dose dependent effect. Both chlorophyll a and chlorophyll b contents were inhibited with increase in selenate concentrations. The effect w as more pronounced in cv. s atabdi compared to cv. k hitish .The level of accessory pigments w as deferentially affected by s elenium treatment . Simultaneously , the f luorescence intensity and H ill activity decreased with increase in selenate concentrations in the test seedlings. It is assumed that s elenium plays a protective role in plants subjected to stress and prevents the formation of reactive oxygen species (ROS) in the cells. Higher selenate concentrations (≥20 μM) exerted variable effect on the activities of enzymatic antioxidants viz.; s uperoxide dismutase (SOD), catechol peroxidase (CPX) and c atalase (CAT) in the test seedlings. The activity of SOD increased with increase in selenate concentrations, whereas activities of CAT and CPX decreased. Under high selenate concentrations, the levels of oxidative stress markers, viz.; proline, H _( 2 ) O _( 2 ) and MDA were also enhanced. Selenium induced accumulation of total soluble sugar and increased the level of both reducing and non reducing sugars in both the test cultivars. The starch contents concomitantly decreased with rise in selenate concentrations. Moreover , the nutrient contents of test seedlings were significantly influenced by s elenium. The Na and K levels gradually increased whereas Ca , Mg and Fe levels decreased on application of selenate. Joint application of 10 mM sulphate and selenate showed significant alterations on all parameters tested with respect to selenate treatment alone. Partial to complete amelioration occurred in the test seedlings treated with high concentrations of selenate and sulphate. Our study shows that selenium at low concentration had a stimulatory effect on growth and metabolism as against high concentration s which proved to be toxic to the rice seedlings obtained from both the cultivars. Effects were more pronounced in cv. satabdi than in cv. khitish which is considered to be comparatively tolerant to selenium. The dose dependent influence of s elenium on the physiological and biochemical responses of test seedlings may be reversed by co- application with sulphate .