Abstract
The effect of selenate (Na2SeO4) and sulphate (Na2SO4) 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 was more pronounced in cv. satabdi compared to cv. khitish.The level of accessory pigments was deferentially affected by selenium treatment. Simultaneously, the fluorescence intensity and Hill activity decreased with increase in selenate concentrations in the test seedlings. It is assumed that selenium 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.; superoxide dismutase (SOD), catechol peroxidase (CPX) and catalase (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, H2O2 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 selenium. 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 concentrations 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 selenium on the physiological and biochemical responses of test seedlings may be reversed by co-application with sulphate.
Highlights
Selenium (Se), belonging to oxygen sulphur family, acts as an essential micronutrient as well as an antioxidant in microbes and animals but its role in plants is debatable
A marked inhibition in growth of rice seedlings with increase in concentrations of selenium were observed in both roots and shoots of cv. satabdi and cv. khitish (Figure 1(a) and Figure 1(b))
At 2 μM selenate, the root length increased on an average, by about 5% whereas for shoot the increase was by about 3% over water control in cv. satabdi
Summary
Selenium (Se), belonging to oxygen sulphur family, acts as an essential micronutrient as well as an antioxidant in microbes and animals but its role in plants is debatable. Selenium possesses antidiabetic, immunostimulating, cardio-protective, antiviral, anti-carcinogenic and detoxification properties [1]. Plant sources of selenium are more bioavailable than animal sources but the translocation of selenium from root to shoot is dependent on the form of selenium supplied [2]. Se is primarily absorbed as selenite or selenate from soil. It is translocated to the chloroplast, where it follows the sulfur assimilation pathway [3]. Selenium and sulphur being chalcogens compete readily for their uptake in plants as both anions are taken up via sulphate transporter(s) in the root plasma membrane [4] [5]
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