Alleviation of Salt Stress in Seedlings of Black Glutinous Rice by Seed Priming with Spermidine and Gibberellic Acid

Abstract

This study was carried out to elucidate the spermidine (Spd) and gibberellic acid (GA₃) priming-induced physiological and biochemical changes responsible for induction of salinity tolerance in two rice (Oryza sativa L.) cultivars, namely ‘Niewdam Gs. no. 00621’ (salt tolerant) and ‘KKU-LLR-039’ (salt sensitive). The seeds of the two cultivars were primed separately with distilled water, 1 mM Spd or 0.43 mM GA₃. Primed seeds were germinated and the resultant seedlings were hydroponically grown for 14 days before being exposed to salinity stress (150 mM NaCl) for 10 days. Seed priming with Spd or GA₃ slightly improved salt-induced reductions in growth, anthocyanin and chlorophyll contents of the seedlings. Salt stress induced pronounced increases in Na⁺/K⁺ ratio, proline and H₂O₂ contents, particularly in the sensitive cultivar. The levels of these salt-sensitivity physiological indicators tended to be mitigated by priming with Spd and GA₃. Salt-stressed seedlings grown from seeds primed with these growth regulators also possessed higher phenolic contents and greater antioxidant capacity than the control seedlings. Based on all growth and physiological data, Spd tended to be more effective than A₃ in improving salt tolerance in both rice cultivars.