EFFECT OF NITRIC OXIDE ON ALFALFA SEED GERMINATION UNDER NaCl STRESS

The seeds of two alfalfa varieties(Medicago sativa cv.Gannong No.4 and Medicago.sativa cv.Algonquin) pretreated with NO-donor SNP,NO-scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide(c-PTIO),tungstate,the nitrate reductase(NR) inhibitor,nitric oxide synthase(NOS) inhibitor NG-nitro-L-Arg-methyl ester(L-NAME) and sodium ferrocyanide(SNP analogue that does not release NO) were used to study the physiological effect of NO on germination under NaCl stress.The results showed that the germination rate,epicotyl length,hypocotyl length and dry matter of seedlings were inhibited(P0.05),and the activity of α-amylase,β-amylase and protease were decreased,and the hydrolysis of starch and the accumulation of soluble sugar were inhibited(P0.05) under NaCl stress.The activity of protease,α-amylase and β-amylase was increased,the starch content was decreased and soluble sugar content was increased,the length of epicotyl and hypocotyls,germination rate and dry matter were increased by adding exogenous NO under NaCl stress(P0.05).The NO-donor SNP analogue(sodium ferrocyanide) had no effect on the germination indices(P0.05);whereas reduction effects on seed germination were found while the c-PTIO,tungstate and L-NAME were applied(P0.05).It could be concluded that NaCl stress inhibited the germination of alfalfa seeds,while the exogenous NO could effectively alleviate the inhibitive effect.Endogenous NO might also involved in the regulation of alfalfa seed germination under NaCl stress,and the NO released through NOS and NR pathway might play an important role in alleviating the inhibitive effect in alfalfa seed germination.