Protective effect of exogenous spermidine on ion and polyamine metabolism in Kentucky bluegrass under salinity stress

Spermidine (Spd) acts as a plant protectant under salinity stress. The objective of this study was to determine whether exogenous Spd pre-treatment could improve the salinity tolerance of Kentucky bluegrass (Poa pratensis L.). Exogenous Spd was applied before the grass was exposed to 200 mM sodium chloride (NaCl) for 28 d in the growth chamber. Salinity stress decreased chlorophyll (Chl) content, K+/Na+ ratio and K+, Ca2+, and Mg2+ contents, and increased electrolyte leakage (EL), proline, Na+, putrescine (Put), Spd and Spermine (Spm) levels and the activities of arginine decarboxylase (ADC), ornithine decarboxylase (ODC), S-adenosylmethionine decarboxylase (SAMDC) and polyamine oxidase (PAO). Pre-treatment with 1 mM Spd effectively alleviated the decline of Chl content, K+/Na+ ratio and K+, Ca2+, and Mg2+ contents under salinity stress conditions. Spd pre-treatment also reduced EL, Na+ content, Put levels and the activities of ADC and PAO, but increased proline content, endogenous Spd and Spm levels and the activities of ODC and SAMDC upon salinity stress. These results indicate that exogenous Spd pre-treatment could enhance salinity tolerance by increasing proline levels and regulating ion and polyamine metabolism.