Protective effect of spermidine on salt stress induced oxidative damage in two Kentucky bluegrass (Poa pratensis L.) cultivars.

To improve the salinity tolerance of turfgrass and investigate the effect of spermidine (Spd) on antioxidant metabolism and gene expression under salinity stress condition, exogenous Spd was applied before two kentucky bluegrass (Poa pratensis L.) cultivars ('Kenblue' and 'Midnight') were exposed to 200 mM sodium chloride (NaCl) stress for 28 d. Salinity stress decreased the turfgrass quality, increased the content of malonyldialdehyde (MDA), superoxide anion (O₂(·-)) and hydrogen peroxide (H₂O₂), and enhanced activities of superoxide dismutase (SOD), catalase (CAT), guaiacol peroxidase (POD) and ascorbate peroxidase (APX) and isozymes intensity in both cultivars. In addition, the expression level of Cu/ZnSOD was down-regulated in 'Kenblue' but up-regulated in 'Midnight' after salt treatment. Salinity stress also enhanced the expression of APX but inhibited the expression of CAT and POD in both cultivars. Exogenous Spd treatment alleviated the salinity-induced oxidative stress through decreasing MDA, H₂O₂ and O₂(·-) contents in both cultivars. Besides, exogenous Spd further enhanced the activities of SOD, CAT, POD and APX accompanied with the increased intensity of specific isozymes of SOD, CAT and APX in both cultivars and POD in 'Kenblue'. Moreover, Spd further up-regulated expression levels of Cu/ZnSOD and APX, but down-regulated those of CAT and POD in both cultivars. These results indicated that exogenous Spd might improve turfgrass quality and promote the salinity tolerance in the two cultivars of kentucky bluegrass through reducing oxidative damages and increasing enzyme activity both at protein and transcriptional levels.