Effects Of Exogenous Spermidine On Salinity Tolerance In Two Kentucky Bluegrass Cultivars

Saline water irrigation is an important way to solve the shortage of fresh water resources, but it will result in the salinity stress which is among the main factors limiting the turf quality and growth. Thus, it is necessary to improve the salinity tolerance of turfgrass. Since Spd is known to act as a plant protectant under salinity stress, the objective of this study was to determine whether exogenous Spd application could improve the salinity tolerance in two Kentucky bluegrass (Poa pratensis L.) cultivars (’Kenblue’ and ’Midnight’) when they were seedlings and established turfs, respectively. To the seedlings,1 mM exogenous Spd was added in a MS medium supplemented with 200 mM NaCl before the two cultivars were transferred to it. To the established turfs, exogenous Spd was applied before the two cultivars were exposed to 200 mM NaCl for 28 d in growth chambers. The main results were as followed:1 The stage of seedlings:Under salinity stress, exogenous Spd alleviated both shoot and root growth inhibition and significantly increased the antioxidant activities of APX, CAT, POD, SOD and Pro content. It also significantly decreased the EL and the content of H2O2, O2·- and MDA. Furthermore, Spd maintained ion balance by reducing Na+ content and increasing the contents of K+, Ca2+ and Mg2+, improving proper intracellular ion compartmentalization and stabilizing the membrane’s structure. Thus, exogenous Spd could improve the salinity tolerance in the seedlings of two Kentucky bluegrass cultivars.2 The stage of established turfs:Under salinity stress, exogenous Spd effectively alleviated the decline of TQ, RWC, Chl content, destruction of ion homeostasis, and reduced EL, MDA content and the accumulation of H2O2 and O2·-. Exogenous Spd alleviated the salinity-induced injury through increasing the Pro content, preventing the influx of Na+ and the loss of K+, Ca2+ and Mg2+, further increasing the SAMDC activity, reducing ADC and PAO activity, maintaining high level of endogenous free Spd and Spm levels accompanied with low endogenous free Put level, and further enhancing 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, exogenous Spd further up-regulated Cyt APX and down-regulated CAT and POD in both cultivars, and enhanced the expression of Ch11 Cu/ZnSOD and Cyt Cu/ZnSOD in ’Midnight’ and Ch1 Cu/ZnSOD and MnSOD in ’Kenblue’. Thus, exogenous Spd could improve the salinity tolerance in two Kentucky bluegrass cultivars when they were established.These results indicated that exogenous Spd application might enhance the salinity tolerance by regulating polyamine metabolism and increasing enzyme activity both at protein and transcript levels and thereby sustaining ionic homeostasis and osmotic adjustment and reducing oxidative damages and ion toxicity. In summary, exogenous Spd could improve the salinity tolerance in two Kentucky bluegrass cultivars, no matter when they were seedlings or established turfs.