Application of Exogenous Spermidine (Spd) Improved Salt Tolerance of Rice at the Seedling and Reproductive Stages

Abstract

Rice productivity in many areas is affected by salinity stress. Application of plant growth regulators may reduce the damage caused by salinity. This study aimed to alleviate salt stress damage using spermidine (Spd) as priming agents and spraying. Two cultivars of rice (Oryza sativa L.) including, Niewdam Gs.no.00621 (salt-tolerant) and KKU-LLR-039 (salt-sensitive) were used in this study. At seedling stage, the seeds of the two cultivars were primed separately with distilled water and 1mM Spd. Primed seeds were germinated and the resultant seedlings were hydroponically grown for 21 days before being exposed to salinity stress (150mM NaCl) for 10 days. Seed priming with Spd improved salt-induced reductions in growth. Salt stress induced pronounced increases in Na+/K+ ratios which were significantly reduced in the seedlings grown from Spd-primed seeds. Priming rice seeds with Spd also resulted in seedlings which possessed higher anthocyanin, phenolic contents and greater antioxidant capacity (based on DPPH, ABTS and FRAP assay) than the control seedlings. For reproductive stage, the plants were grown in pots until early booting stage. Thereafter, the plants were sprayed with 1mM Spd for 7 days before being stressed by adding 25mM NaCl until harvest. Pretreatment by foliar spraying of Spd to rice plants during the early booting stage significantly improved yields particularly of the salt-sensitive KKU-LLR-039. Spd pretreatment resulted in a reduction in Na+/K+ ratio in rice grains. Moreover, pretreatment with Spd further increased anthocyanin, phenolic content and antioxidant capacities (DPPH, ABTS and FRAP) in mature grains both rice cultivars.