Sodium Selenate Treatment Using a Combination of Seed Priming and Foliar Spray Alleviates Salinity Stress in Rice

Abstract

Soil salinity is one of the important abiotic stress factors that affect rice productivity and quality. Research with several dicotyledonous plants indicated that the detrimental effects associated with salinity stress can (partly) be overcome by the external application of antioxidative substances. For instance, sodium selenate (Na2SeO4) significantly improved the growth and productivity of several crops under various abiotic stress conditions. At present there is no report describing the impact of Na2SeO4 on salinity stressed cereals such as rice. Rice cultivation is threatened by increasing salinity stress, and in future this problem will further be aggravated by global warming and sea level rise, impacting coastal areas. The current study reports on the effect of Na2SeO4 in alleviating salinity stress in rice plants. The optimal concentration of Na2SeO4 and the most efficient mode of selenium application were investigated. Selenium, sodium, and potassium contents in leaves were determined. Antioxidant enzyme activities as well as proline, hydrogen peroxide (H2O2), and malondialdehyde (MDA) concentrations were analyzed. In addition, the transcript levels for OsNHX1, an important Na+/H+ antiporter, were quantified. Treatment of 2-week-old rice plants under 150 mM NaCl stress with 6 mg l-1 Na2SeO4 improved the total biomass. A significantly higher biomass was observed for the plants that received Na2SeO4 by a combination of seed priming and foliar spray compared to the individual treatments. The Na2SeO4 application enhanced the activity of antioxidant enzymes (SOD, APX, CAT, and GSH-Px), increased the proline content, and reduced H2O2 and MDA concentrations in plants under NaCl stress. These biochemical changes were accompanied by increased transcript levels for OsNHX1 resulting in a higher K+/Na+ ratio in the rice plants under NaCl stress. The results suggest that Na2SeO4 treatment alleviates the adverse effect of salinity on rice plant growth through enhancing the antioxidant defense system and increase of OsNHX1 transcript levels.

An Overview of Hazardous Impacts of Soil Salinity in Crops, Tolerance Mechanisms, and Amelioration through Selenium Supplementation

“…Moreover, enhanced growth and nutritional qualities of spinach (Spinacia oleracea L.), ryegrass (Lolium perenne L.), wheat (Triticum aestivum L.), and mung bean (Vigna radiate L.) have also been reported by exogenously applied Se under stressed and non-stressed conditions [22,106,142,146]. Further, a lower Na + concentration and higher K + /Na + ratio was observed in selenite-treated plants as compared to untreated plants [27]. Se might have decreased the accretion of Na + ions which led to an increased K + /Na + ratio in comparison to the untreated control plants of dill (Anethum graveolens) and garlic (Allium sativum L.) [129,147].…”

“…Some studies have shown that Se is an essential element for human and animal, which plays some beneficial roles in higher plants. Selenium application caused an increasing growth in rice (Oryza sativa L.) [27] and wheat (Triticum aestivum L.) [28], under both stressed and non-stressed conditions. Se has been demonstrated to regulate plant growth by strengthening the stress tolerance mechanisms such as antioxidant and secondary metabolite metabolism [29].…”

“…Theses enzymes in turn are responsible for the upgradation of chlorophyllase activity [66] or a reduction in leaf water potential, N uptake, and thereby, the reduced photosynthetic capacity of plants [53]. Chlorophyll degradation might also be carried out by salinity-induced superoxide radicals and H 2 O 2 , which degrade the membranes of thylakoids and chloroplast [27].…”

“…The accumulation of higher levels of Na + ions in plant roots under salinity stress causes a reduction in hydraulic conductivity and ultimately lowered relative water contents (RWC); however, the Se (Na 2 SeO 4 ) supply reduced Na + ions and improved root growth, and thereby, might have enhanced the water supply to shoots and sustained plant growth [27,139]. Salt-affected soils cause hindrances in nitrogen assimilation, accumulation, and metabolism, and hence, disturb the proline (a molecular chaperone responsible for maintaining protein integrity) biosynthetic mechanism [140,141].…”

“…Under salinity stress, lowered H 2 O 2 contents were observed in Se-treated canola (Brassica napus L.) plants [136]. Meanwhile, plants exposed to Se showed lower concentrations of MDA under NaCl stress, showing that Se was vital in bringing down the lipid peroxidation by amending the antioxidant enzymes and protecting the membranous structures of Oryza sativa L. [27], Cucumis sativus L. [124], Brassica napus L. [24], and Anethum graveolens [147]. In addition, it was noticed that lipid peroxidation (MDA) production was reduced by elevating Se concentration under salt stress [127].…”