Effects of 6-Benzyladenine, γ-Aminobutyric Acid, and Nitric Oxide on Plant Growth, Photochemical Efficiency, and Ion Accumulation of Perennial Ryegrass Cultivars to Salinity Stress

Plant growth regulators (PGRs) can mediate plant response to salinity stress. Perennial ryegrass (Lolium perenne) cultivars of BrightStar SLT, Catalina, Inspire, and SR4660ST were exposed to 0, 100, or 200 mM NaCl for 14 d. 6-benzyladenine (6-BA, 10 mM), gamma-aminobutyric acid (GABA, 500 mM), nitric oxide (NO, 200 mM), and H2O were applied to the foliage every day for 3 days before stress and then every 2 days during salinity stress. Averaged across the four cultivars, a foliar spray of NO increased leaf fresh weight (FW) and dry weight (DW) at 0 mM NaCl, whereas application of 6-BA increased DW and GABA reduced Na+ concentration at 100 mM NaCl, compared with H2O application. Plants treated with 6-BA, GABA, and NO had less chlorotic and necrotic leaf tissue than plants treated with H2O at 200mM NaCl. Spray of 6-BA and NO increased FW and DW, but application of all three PGRs maintained higher leaf photochemical efficiency and lower leafNa(+) concentration compared with H2O treatment at 200mM NaCl. Across salinity and PGR treatments, 'Catalina' exhibited higher plant height than the 'Inspire' and SR4660ST, and SR4660ST had relatively higher Na+ concentration than 'Catalina' but not 'BrightStar SLT' and 'Inspire'. The results demonstrate that 6-BA, GABA, and NO ameliorated salinity tolerance of perennial ryegrass by improving growth and photochemical efficiency or reducing Na+ accumulation.