香根草对镉毒害的生理响应——采用傅里叶变换红外光谱法(FTIR)

Physiological responses of Vetiveria zizanioides to cadmium stress by fourier transform infrared spectroscopy

为阐明香根草(Vetiveria zizanioides)对镉(Cd^2+)胁迫的耐性机理及其对重金属Cd2+的积累特征,通过水培试验,采用傅里叶变换红外光谱法(FTIR)研究在不同Cd^2+浓度处理时香根草根、茎、叶化学组分的变化,同时测定香根草叶Cd2+的亚细胞分布和其重金属Cd^2+含量。结果表明,其根组织在2927 cm^-1处峰高先下降后上升,表明在低Cd^2+(Cd^2+<3 mg/L)处理条件下香根草分泌的有机酸不断螯合Cd^2+,造成羧酸O—H的减少,但随着Cd2+含量的升高,其羧酸螯合力变弱,有机酸含量渐渐升高;茎组织在1631 cm-1峰高处先上升后下降,表明在低Cd^2+(Cd^2+<3 mg/L)处理条件下香根草产生氨基酸、多肽和蛋白质等物质,通过渗透调节来增强抗逆性,但随着Cd^2+含量的升高,蛋白质二级结构中肽键间氢键的结合力受影响较大。当Cd^2+处理浓度为7 mg/L时,香根草生长10 d后,地上部分及根组织富集Cd^2+量分别高达212.49 mg/kg和290.59 mg/kg。香根草地上部分的Cd^2+含量随Cd2+处理浓度的增加而增加。香根草叶片富集的Cd^2+主要分布于细胞质中,其次为细胞壁,而在线粒体和叶绿体中含量最低。

Heavy metal pollution caused by industrial sewage and agricultural production is becoming an increasingly serious problem.Cadmium(Cd)is one of the most phytotoxic heavy metal elements and is attracting increasing research attention.It easily enters the food chain and poses considerable threat to human health.Vetiveria zizanioides is a tall(1—2 m),fast growing,and perennial tussock grass that is eurytopic in terms of habitat choice.It develops a long(3—4 m),massive,and complex root system that can penetrate the deeper layers of the soil.V.zizanioides has a strong tolerance for Cd,and it can adapt to tolerate Cd at low concentrations over a long period,or high Cd concentrations over a short period.The Cd can be absorbed and stored by V.zizanioides while retaining its stability.Healthy and equal sized plants were chosen,cleared,and cultured for 7 days in complete Hoagland nutrient solution.After the plants had grown buds,they were treated with different gradients of Hoagland′s solution modified by adding Cd with cadmium sulfate(1∶1)hydrate(3∶8)(3CdSO4·8H2O)to create Cd concentrations of 0,1,3,5,and 7 mg/L.The experiments were carried out separately in three different groups.The plants were harvested after 10 days.The whole plant was washed under tap water and rinsed with deionized water.The roots,stems,and leaves were separated,put into a cabinet dryer at 105℃for 30 min,further dried in a cabinet dryer at 80℃for a another 48 h and finally milled into a fine powder(less than 200 mesh)with a stainless steel attritor.This study deals with the physiological response of the changes in chemical contents in the root,stem,and leaf of V.zizanioides seedlings stressed by excess cadmium ions(Cd^2+)using the Fourier transform infrared spectroscopy technique(FTIR).Cadmium(Cd)accumulation in plants and its subcellular distribution(determined by atomic absorption spectroscopy)were tested under the different Cd^2+concentrations to elucidate the mechanism of Cd^2+tolerance and the accumulation characteristics of Cd^2+in V.zizanioides.This result indicates that after an initial decline,absorbance in roots of the dominant infrared band(near 2927 cm^-1)exhibited an increase.At low Cd^2+concentrations(<3 mg/L),organic acids secreted by V.zizanioides were able to chelate Cd^2+,which leading to a decrease in carboxylic acid O—H.At high Cd^2+concentrations(>3 mg/L),chelating activity decreased,which was followed by an increase in organic acids.After an initial increase,absorbance changes in stems of the dominant infrared band(near 1631 cm-1)exhibited a decline.This indicates that at low Cd^2+concentrations(<3 mg/L),osmosis of organic substances(e.g.amino acids,peptides,and proteins)occurred,improving Cd2+tolerance.However,with the increase in Cd2+concentrations,the binding force between peptide bonds and hydrogen bonds in protein secondary structure was significantly affected.In addition,the plant accumulated large amount of Cd^2+,up to the maximum of 212.49 mg/kg(shoot)and 290.59 mg/kg dry weight(root)after 10 days when the plant was treated with a Cd^2+concentration of 7 mg/L.The Cd^2+in the shoot(stem and leaf)usually increased with increasing Cd^2+concentrations.Cadmium accumulated in leaves was mainly distributed in the cytoplasm,followed by the cell wall,and was least distributed in the mitochondria and chloroplast.This study demonstrates the potential of the Fourier transform infrared spectroscopy as a non invasive and rapid technique for monitoring of plants stressed with heavy metals.