低温对山定子和平邑甜茶幼苗根系氮代谢酶及游离氨基酸的影响

Effects of Low-temperature on Enzymes Activities of Nitrogen Metabolism and Free Amino Acids Contents in Root of Malus baccata Borkh.and Malus hupehensis Rehd.Seedlings

以苹果砧木山定子(Malus baccata Borkh.)和平邑甜茶(Malus hupehensis Rehd.)实生苗为试材,研究低温(昼10℃/夜2℃)对根系氮代谢关键酶活性和氨基酸含量的影响。结果表明:低温诱导山定子和平邑甜茶根系谷氨酰胺合成酶(GS)活性,与常温对照相比两砧木活性分别增加了119%和317%。低温同时降低了谷氨酸合酶(NADH-GOGAT)和谷氨酸脱氢酶(NADH-GDH)活性,两砧木NADH-GOGAT活性分别为常温对照的6.11%和48.43%,NADH-GDH活性分别为常温对照的47.07%和33.84%。低温对平邑甜茶GS活性和NADH-GDH活性的影响大于山定子,说明平邑甜茶对低温胁迫较敏感;山定子根系NADH-GOGAT活性受低温影响较大,而低温对平邑甜茶根系NADH-GOGAT活性没有明显影响。GS/GDH比值分析表明,低温前后根系中铵同化途径均以GS/GOGAT为主,但低温使GS/GOGAT途径在根系中的作用明显加强,尤其对平邑甜茶的效果更明显。低温增加了山定子和平邑甜茶根系游离氨基酸总量,山定子和平邑甜茶分别比对照增加了78.34%和89.79%,平邑甜茶游离氨基酸含量高于山定子。低温处理前根系中游离氨基酸以苏氨酸、酪氨酸、天冬氨酸和谷氨酸为主,低温处理后以苏氨酸、精氨酸、天冬氨酸和谷氨酸为主,低温显著提高了根系精氨酸的含量。

The enzymes activities of nitrogen metabolism and free amino acids were studied under low temperature in Malus baccata Borkh.and M.hupehensis Rehd.The results indicated that at low temperature,glutamine synthetase（GS） activity were increased obviously by 119% and 317% respectively in M.baccata Borkh.and M.hupehensis Rehd.But low temperature decreased glutamate synthase （NADH-GOGAT） and glutamate dehydrogenase （NADH-GDH） activity.In M.baccata Borkh.and M.hupehensis Rehd.NADH-GOGAT activity decreased to 6.11% and 48.43%,NADH-GDH activity decresed to 47.07% and 33.84%.Low temperature effected GS activity and NADH-GDH activity in M.hupehensis Rehd.more than in M.baccata Borkh.Analysis for GS/GDH ratio showed that GS-GDH cycle was the main pathway of ammonium assimilation irrespective of low temperature,but under low temperature stress,GS pathway was strengthened obviously,especially in M.hupehensis Rehd.At low temperature the content of free amino acids were increased by 78.34% and 89.79% respectively in M.baccata Borkh.and M.hupehensis Rehd.,the total content of free amino acids increased more in M.baccata Borkh.than that of M.hupehensis Rehd.Before low temperature the main composition of free amino acids were threonine,tyrosine,aspartic acid and glutamate,but under low temperature the main composition of free amino acids were threonine,arginine,aspartic acid and glutamate.The content of arginine was obviously increased under low temperature.