Effects of Plant Growth Regulators on Salinity Tolerance in Perennial Ryegrass

Salinity stress is a major abiotic stress that affects plant growth and development. Application of plant growth regulators (PGRs) can improve salinity tolerance. The objective of this study was to investigate effects of PGRs effect on growth and physiology of perennial ryegrass (Lolium Perenne) and alterations of endogenous plant hormone under salinity stress in perennial ryegrass cultivars. The reduced plant height, dry weight and fresh weight, and K+ concentration and increased Na+ concentration were observed in four cultivars of Brightstar SLT, Catalina, Inspire and SR4660ST under both 100 mM and 200 mM NaCl. No obvious PGR effects were found in the plants grown under 100 mM NaCl. Foliar application of 6-Benzyladenine (6-BA), abscisic acid (ABA), CaCl2, γ-aminobutyric acid (GABA), nitric oxide donor sodium nitroprusside (SNP), jasmonic acid (JA), salicylic acid (SA), especially 6-BA, GABA and SNP had significantly higher fresh and dry weight, chlorophyll fluoresce and K+ concentration and lower Na+ concentrations under 200 mM NaCl, compared to the plants sprayed with water, but the results varied with PGR and cultivars. Compared to non-stressed plants, 200 mM NaCl increased total soluble protein (TSP) and decreased activities of superoxide dismutase (SOD) catalase (CAT) and peroxidase (POD) in Brightstar SLT and SR4660ST. Application of 6-BA increased CAT and POD activities but decreased TSP in both cultivars, while application of SNP had higher CAT activity in both cultivars and decreased POD activity in SR4600ST under salinity stress, compared to the plants sprayed with water. No obvious effects of GABA application on antioxidant activity were found under salinity stress. Salinity stress (200 mM NaCl) increased zeatin concertation at 5- and 12-d of harvests in SR4660ST, while increased kinetin concentration was found on 1st harvest for SR4660ST and 2nd harvest for Brightstar SLT, compared to their respective non-stress control. Increased indole-3-butyric acid concentration was found in Brightstar SLT and SR4660ST for both harvests under salinity stress, but indole-3-acetic acid content was unaffected. Salinity stress caused 73% reduction of jasmonic acid in Brightstar SLT and 74 % reduction in SR4660ST at 2nd harvest time. Salinity stress also caused 90% reduction of abscisic acid concentration on 1st harvest for Brightstar SLT. The results suggested that alterations of the endogenous hormone could be associated with plant adaption to the salinity stress