壳聚糖对NaCl胁迫下菜用大豆结瘤固氮的影响

【目的】研究壳聚糖对盐胁迫抑制菜用大豆结瘤固氮的缓解效应,为进一步探讨壳聚糖抗逆机理提供新的线索。【方法】以蛭石为基质,以菜用大豆‘特早王’–根瘤菌共生体系为研究对象,采用人工气候箱培养,研究NaCl胁迫下壳聚糖对菜用大豆根瘤形成、生物固氮的影响。菌种为与‘特早王’共生匹配性较好的快生根瘤菌N18。接种后的植株进行如下4个处理:1)叶面喷施清水,根部浇灌无氮营养液(CK);2)叶面喷施壳聚糖水溶液,根部浇灌无氮营养液(CTS);3)叶面喷施清水,根部浇灌溶有NaCl的无氮营养液(Cl);4)叶面喷施壳聚糖水溶液,根部浇灌溶有NaCl的无氮营养液(CTS+Cl)。上述各处理施用的水或水溶液均为无菌水配制,NaCl处理的浓度为50 mol/L,CTS处理的适宜浓度为200 mg/L。接种30天后,将大豆植株取出,用清水将根部蛭石冲洗干净后,立即测定根瘤固氮酶活性、根瘤数及根瘤鲜重,然后测定根瘤豆血红蛋白含量和根系活力,最后测植株干重和全氮量。【结果】氯化钠胁迫下,植株干重显著下降,与CK相比降幅达49%,喷施壳聚糖后(CTS+Cl),降低幅度显著减小,但依然显著低于CK (P <0.05)。无盐条件下,与CK相比,壳聚糖处理(CTS)增加植株干重的效果不明显。喷施壳聚糖显著增加了菜用大豆的根瘤数、根瘤鲜重、植株含氮量、根系活力、豆血红蛋白含量及固氮酶活性(P <0.05)。NaCl胁迫显著抑制了菜用大豆的结瘤固氮作用,其中根瘤数、根瘤鲜重分别较CK下降了79%、90%,而壳聚糖处理(CTS+Cl)使菜用大豆在盐逆境下的结瘤数、根瘤鲜重、植株全氮含量、根系活力、豆血红蛋白含量及固氮酶活性等均显著回升,增幅分别达对照的29%、20%、17%、48%、19%、21%,但均显著低于CK。【结论】非NaCl胁迫下,喷施壳聚糖可以显著促进菜用大豆结瘤,提高豆血红蛋白含量及固氮酶活性,最终增加植株含氮量。在NaCl胁迫下,外源壳聚糖可以显著缓解氯化钠胁迫导致的对根系活力和结瘤固氮的影响。因此,叶面喷施壳聚糖是促进菜用大豆结瘤固氮和生长的有效措施。

Effects of chitosan on nodulation and nitrogen fixation of vegetable soybean under NaCl stress

【Objectives】The effect of stimulating growth and tolerance to salt stress of crop through foliar spray of chitosan was confirmed in this paper.【Methods】Vermiculite culture method was conducted inside plant growth chamber, vegetable soybean Glycinemax (L.) Merr.] ‘Tezaowang’ and the rhizobium N18 were used as the test materials in the symbiotic system of vegetable soybean-rhizobium. Salt stress was prepared by adding 50 mol/L of NaCl in nitrogen-free nutrient solution and chitosan (CTS) spraying concentration was 200 mg/L in the treatments. Four treatments were setup including spraying water and no salt stress control (CK), spraying CTS under no salt stress (CTS); spraying water under salt stress (Cl) and spraying CTS under NaCl stress (CTS +Cl). After 30 days treatment, the plants were harvested, and the activities of nitrogenase, the number and fresh weight of nodules were measured immediately. Then the root activity and leghemoglobin content were determined, and the plant dry biomass and total N content were tested at last.【Results】Without NaCl stress, spraying CTS did not increase the dry plant biomass significantly; Under NaCl stress, the fresh biomass was significantly decreased, and spraying CTS narrowed the decrease significantly but still lower than that in CK (P < 0.05). Without NaCl stress, the nodule number, nodule fresh weight, total N content, root activity, leghemoglobin content and nitrogenase activity of vegetable soybean were significantly increased by spraying CTS. Under NaCl stress, the nodulation and nitrogen fixation of vegetable soybean were significantly inhibited, while spraying CTS significantly increased the nodule umber, nodule fresh weight, total nitrogen content, root activity, leghemoglobin content and nitrogenase activity of vegetable soybean under salt stress, with the increase of 29%, 20%, 17%, 48%, 19%, 21% of the CK respectively, although they were still significantly lower than CK.【Conclusions】Under normal condition, spraying chitosan shows significant effect in promoting the nodulation, enhancing the leghemoglobin content and nitrogenase activity, and increase plant growth as a result. Under NaCl stress, spraying chitosan could significantly increase the tolerance of crop to salt stress, although could not offset the diverse effect of salt stress completely. Therefore, foliar application of exogenous chitosan is recommended in the production of legumes.