Effect of exogenous selenium supply on photosynthesis, Na+ accumulation and antioxidative capacity of maize (Zea mays L.) under salinity stress

Abstract

The mechanism of selenium-mediated salt tolerance has not been fully clarified. This study investigated the possible role of selenium (Se) in regulating maize salt tolerance. A pot experiment was conducted to investigate the role of Se (0, 1, 5 and 25 μM Na2SeO3) in photosynthesis, antioxidative capacity and ion homeostasis in maize under salinity. The results showed that Se (1 μM) relieved the salt-induced inhibitory effects on the plant growth and development of 15-day-old maize plants. Se application (1 μM) also increased the net photosynthetic rate and alleviated the damage to chloroplast ultrastructure induced by NaCl. The superoxide dismutase (SOD) and ascorbate peroxidase (APX) activities were increased, and ZmMPK5, ZmMPK7 and ZmCPK11 were markedly up-regulated in the roots of Se-treated plants, likely contributing to the improvement of antioxidant defence systems under salinity. Moreover, 1 μM Se increased K+ in the shoots while decreasing Na+ in the roots, indicating that Se up-regulates ZmNHX1 in the roots, which may be involved in Na+ compartmentalisation under salinity. The findings from this single experiment require repetition together with measurement of reactive oxygen species (ROS), but nevertheless suggest that exogenous Se alleviates salt stress in maize via the improvement of photosynthetic capacity, the activities of antioxidant enzymes and the regulation of Na+ homeostasis.

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

“…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]. It has also been reported previously that Se reversed the negative impacts of soil salinity on the photochemical efficiency of photosystem II [30].…”

“…Likewise, another study reported that Se application (20 µM) in the form of sodium selenite causes improvements in the growth and yield of eggplants under varying levels of soil salinity [123]. However, higher doses of selenite were found to have deleterious effects on the growth and development stages of maize under a salt stress of 100 mM NaCl [29]. Even though Se is an essential trace nutrient to humans and other animals as an antioxidant, Se toxicity might appear at higher concentrations due to the substitution of S with Se in the structure of amino acids, followed by the inaccurate folding of proteins and thus the creation of nonfunctional proteins and enzymes [102].…”

“…Once excess Na + and Cl −1 are vacuolated, this significantly lowers the osmotic potential without any change in the metabolic process rate and ultimately contributes to osmoregulation [57]. Many experiments have emphasized this strategy, where the overexpression of vacuolar Na + /H + antiporter gene (NHX1) family has enhanced the salinity tolerance of tomato (Solanum lycopersicum L.) [81], rice (Oryza sativa L.) [82], and maize (Zea mays L.) [29]. More recently, a novel virus-induced gene silencing (VIGS) method has been applied to study the function of GhBI-1 gene in cotton regarding the salt-stress response [83].…”

“…A variety of adaptive mechanisms at the molecular level are involved in overcoming the harmful effects of salinity-induced oxidative stress. Some of the most important are the up and downregulation of gene transcripts [29,95,96], changes of chemical composition and the rigidness of plant's cell wall [97]. It was reported that the expression of antioxidant defense genes is stimulated in Zea mays L. shoots [98], while Rodríguez-Kessler found that two genes, Zmodc and Zmspds2A, are responsible for salinity tolerance in maize roots through the accumulation of polyamine and spermidine [99].…”

“…Salinity stress in particular not only damages a plant's osmotic potential, but also accompanies various secondary stresses, such as cellular oxidative damage by the over-generation of reactive oxygen species (ROS) [122]. The maintenance of ROS homeostasis and other physiological functions such as photosynthesis are the chief priorities of plants exposed to salinity stress [29]. Therefore, finding suitable approaches to understand and investigate the mechanisms underpinning plant responses to salinity stress is essential to sustain agricultural production in saline soils.…”