NaCl胁迫下壳聚糖促进菜用大豆根毛生长和根尖内源IAA积累的机理

Chitosan promotes root hair growth and endogenous IAA accumulation in root tips of vegetable soybean under NaCl stress

【目的】研究外源壳聚糖对NaCl胁迫下菜用大豆根毛生长和根尖内源IAA积累的影响,为进一步研究壳聚糖提高菜豆抗盐性和结瘤能力提供理论基础。【方法】以菜用大豆品种‘绿领八号’-慢生型根瘤菌USDA 122的共生体为试材进行了无土栽培试验。试验设4个处理:根部浇灌无氮营养液条件下,叶面喷蒸馏水(CK)、喷200 mg/L壳聚糖水溶液(T1);根部浇灌含50 mmol/L NaCl的无氮营养液条件下,叶面喷蒸馏水(T2)、200 mg/L壳聚糖水溶液(T3)。在NaCl胁迫处理后2、3、4、5天时,测定菜豆幼苗根毛数量、形态、变形根毛数,分析根尖内源IAA含量、吲哚乙酸氧化酶(IAAO)、过氧化物酶(POD)活性,分析根系丙二醛(MDA)含量。在NaCl处理30天时测定结瘤数、根瘤鲜重、植株含氮量及植株干重。【结果】外源壳聚糖处理(T1、T3)显著提高了NaCl胁迫和无胁迫下菜用大豆的结瘤数、根瘤重、植株含氮量和植株干重,T3较T2的增幅分别达84%、151%、20%和54%,T1处理较CK的增幅分别为38%、18%、12%和7%。外源壳聚糖处理(T1、T3)显著提高了NaCl胁迫和无胁迫下菜用大豆的根毛总数、根毛密度、根毛长度、变形根毛数以及根尖内源IAA含量,显著缩短了NaCl胁迫下根毛起始距离,降低了根尖IAAO和POD活性,同时显著降低了根系MDA含量。【结论】NaCl胁迫下,外源壳聚糖可通过降低IAAO和POD活性,减少IAA的氧化分解;通过缓解根系膜脂过氧化,维持生物膜的相对稳定性和完整性,促进IAA向根尖的极性运输,提高根尖内源IAA含量,诱导根毛形成和生长,进而提高变形根毛数,最终促进了NaCl胁迫下菜用大豆根系的生长和结瘤能力。

【Objectives】Exogenous chitosan could increase the nodulation of vegetable soybean under salt stress.We studied the root hair growth and the accumulation of endogenous IAA in root tip of vegetable soybean under NaCl stress,to provide new clues to further understand study of the promotion mechanism of chitosan.【Methods】Vermiculite cultivation was adopted,the test material was the symbiosis of vegetable soybean variety‘Green Collar VIII’-slow-growing rhizobium USDA 122.Four treatments were set up in the experiment:nitrogen-free nutrient solution was watered on the roots,distilled water was sprayed on the foliage(CK),and 200 mg/L chitosan aqueous solution was sprayed(T1);N-free nutrient solution containing 50 mmol/L NaCl was watered on the roots,and distilled water was sprayed on the foliage(T2);200 mg/L chitosan aqueous solution was sprayed(T3).At 2,3,4,and 5 days after NaCl stress treatment,the number and morphology of seedling root hairs and the number of deformed root hairs were counted,and the endogenous IAA content,indole acetic acid oxidase(IAAO)and peroxidase(POD)activities of the root tips,as well as the malondialdehyde(MDA)content of the root system were analyzed.The number of nodules,fresh weight of rhizomes,nitrogen content of plants and dry weight of plants were determined at 30 days of NaCl treatment.【Results】1)Exogenous chitosan significantly increased the nodule number,nodule weight,plant N content,and plant dry weight of vegetable soybeans by 84%,151%,20%,and 54%under NaCl stress compared to T2,and by 38%,18%,12%,and 7%under no stress compared to CK.2)Exogenous chitosan significantly increased the total number of root hairs,root hair density,root hair length,number of deformed root hairs,and endogenous IAA content in root tips regardless of NaCl stress or not.3)Exogenous chitosan significantly shortened the initial distance of root hairs,reduced the IAAO and POD activities in root tips,and reduced the MDA content in roots under NaCl stress.【Conclusions】Under NaCl stress,exogenous chitosan could reduce the oxidative decomposition of IAA by decreasing the activities of IAAO and POD,maintain the relative stability and integrity of the biofilm by alleviating the lipid peroxidation of the root membrane,promote the polar transport of IAA to the root tip,increase the content of endogenous IAA in the root tip,and induce the formation and growth of root hairs,resulting in the increased number of deformed root hairs,which may be one of the important mechanisms for chitosan to improve the tumor-forming capacity of vegetable soybean.