烟草幼苗根系分泌自毒物质种类及PAEs对根系抗氧化性能的影响

摘要

采用GC-MS技术鉴定水培烟草Burley及K326在幼苗期不同生长阶段的根系分泌物;并用不同浓度邻苯二甲酸二丁酯(DBP)、邻苯二甲酸二异辛酯(DIOP)溶液浇灌盆栽烟草幼苗,研究其根系抗氧化性能变化.结果如下:(1)Burley根系分泌物主要有3类化合物,其中自毒物质邻苯二甲酸酯(PAEs)在二叶龄期、四叶龄期、六叶龄期的相对含量分别为7.6％、0.3％、未检出;而K326根系分泌物主要有9类化合物,PAEs在二叶龄期、四叶龄期、六叶龄期的相对含量分别为35.6％、51.3％、2.2％.(2)浓度高于0.1 mmol/L的PAEs使根中超氧阴离子自由基产生的速率显著(P＜0.05)增加;随着DIOP及DBP浓度的增加,超氧化物歧化酶、过氧化氢酶活性增加,在0.5 mmol/L时达到最大,然后随着处理浓度的增加而下降.丙二醛的浓度随着这两种PAEs处理浓度的增加而增大.结果表明:烟草根系分泌的自毒物质PAEs达到0.5 mmol/L时,能降低根系的抗氧化性能,造成根尖细胞膜系统的氧化损伤,引起根吸收功能等一系列生理生化变化,并最终表现出自毒作用.%Root exudates of two varieties (Burley and K326) of tobacco seedlings cultured in a hydroponic medium were collected,and identified using gas chromatography-mass spectrometry (GC-MS).Further,the effects of different concentrations of dibutyl phthalate (DBP) and diisooctyl phthalate (DIOP) on root antioxidant capacity were assessed using pot culture experiments.The results revealed three main compounds in Burley root exudates.The relative content of autotoxin phthalate esters (PAEs) at the two-,four-,and six-leaf stages were 7.6％,0.3％,and not detected,respectively.However,there were nine main compounds in K326 root exudates.The relative PAE content at the two-,four-,and six-leaf stages were 35.6％,51.3％,and 2.2％,respectively.PAEs such as DIOP and DBP were identified as the major autotoxins in root exudates of both tobacco seedlings.The rate of superoxide anion radical generation in roots significantly increased at concentrations greater than 0.1 mmol/L DIOP and DBP (P ＜ 0.05).Both superoxide dismutase and catalase activities increased with increasing DIOP concentrations,with a peak at 0.5 mmol/L,and subsequently decreased at higher concentrations.Accumulated malondialdehyde concentrations increased with increasing DIOP and DBP concentrations,and the magnitude of malondialdehyde content was DIOP ＞ DBP,which indicated the order of their toxic effect.Finally,our findings also revealed that when PAEs reached 0.5 mmol/L,they decreased the antioxidant capacity of the root system,initiated oxidative damage of the root cell membrane system,and caused a further decrease in root absorption and mineral metabolism,and thereby led to autotoxicity in the tobacco plants.