Exogenous abscisic acid(ABA) and silicon (Si) promote salinity tolerance by reducing sodium (Na + ) transport and bypass flow in rice (Oryza sativa indica)

Excessive sodium (Na+) and chloride (Cl-) concentrations in rice shoots reduce seedlings growth. In a hydroponic study, we investigated the role of abscisic acid (ABA) seed pre-treatment on growth of salt-stressed rice, in the presence and/or absence of silicate (Si). Caryopses of rice IR4630 (salt tolerant) and IR15324 (salt sensitive) were soaked in an ABA solution (10-5 M) for 24 h, and the plants were then allowed to grow in a medium without or with silicate (Si, 0 or 3 mM). Twenty-one-day-old plants were salinised with NaCl (50 mM).We found the application ABA+Si the most effective treatment for improving plant growth under saline conditions. Si treatment alone or with ABA significantly increased the plant total dry biomass under saline or non-saline conditions, whereas, the effect of ABA seed pre-treatment was significant only on total dry biomass of salt sensitive genotype IR15324. Under saline conditions, ABA, Si and ABA+Si application ameliorated plant growth via suppression of Na+ accumulation in shoots and lowering down Na+/K+ ratios in both the rice genotypes. In addition, treatment with Si alone or with ABA significantly reduced Na+ concentrations in the leaf blades and sheaths, increased net assimilation rate and stomatal conductance of salt affected rice seedlings. We concluded that silicon can be applied as a nutrient for rice under saline or non-saline conditions. Furthermore, seed soaking with ABA has a potential for enhancing salt tolerance, particularly in the sensitive rice genotypes.