Study On Response Of Soybean To Aluminum Toxicity

1.The spectra of root,stem,leaf of soybean(Glycine max(L.)Merrill) samples with 0,20,40,60mg/L Al³⁺was determined by Fourier Transform Infrared(FTIR)spectrometry with OMNI-sampler directly,fast and accurately.Little difference was found between the spectra of control leaves of two soybean cultivars,aluminum-resistant cultivar Zhechun NO.2 and aluminum-sensitive cultivar Zhechun NO.3,except the indices of wave number-absorbance from 928 cm^-1to 1200 cm^-1,and similar results were also observed in stem and root samples of two soybean cultivars with 0 mg/L Al³⁺.However,results from the comparison of the spectra showed some distinguishable differences in the intensity and the shape of absorption peaks of their FTIR spectra between the indices of wave number-absorbance from 721 cm^-1to 3366 cm^-1of Al-stressed samples and control samples of two soybean cultivars,and more evident differences of FTIR were exhibited in Al-stressed roots,stems and leaves with the higher concentration of Al³⁺. The increasing absorbance of 2929 cm^-1and 3350 cm^-1was found in root FTIR spectra with 20,40,60 mg/L Al³⁺,while roots got maximum absorbance at wave number of 1375 cm^-1with 20 mg/L Al³⁺,decreased with higher concentration of Al³⁺,and same results showed at wave number of 1410,1423,1549 and 1645 cm^-1.Absorption peak appeared maximum at wave number of 1051,2850,2929 and 3350 cm^-1in stem FTIR spectra with 60 mg/L Al³⁺.There was little difference between the spectra of Al-stressed leaves and controls at wave number from 1750 cm^-1to 2750 cm^-1, but visible difference in leaf spectra was exhibited at other wave number. Moreover,the results showed that the FTIR spectra of aluminum-sensitive cultivar Zhechun NO.3 indicated much more observable differences than aluminum-resistant cultivar Zhechun NO.2 with different concentration of Al,comparing their spectra,implying the material metabolize of aluminum-sensitive soybean was evidently affected by Al,especially. Therefore,providing exact outcome,FTIR spectra could be used broadly for the identification of the endurance of different soybean cultivars to Al.2.Root growth of soybean was markedly inhibited by the exposure to 3 mmol/L Al solution,and the inhibitory of root in aluminum-sensitive cultivar Zhechun NO.3 was more serious than aluminum-resistant cultivar Zhechun NO.2.Moreover,reduction of relative root elongation rate was found with time of exposure to Al.3.Al entered mitochondria and effected the respiration by disturbing the function of mitochondrial membrane.Difference in radical respiration rate between two soybean cultivars was occurred with 0,0.5,3 mmol/L Al. Zhechun NO.3 showed notable reduction of radical respiration rate with Al, while enhancement of respiration rate was found in Zhechun NO.2 with 0.5 mmol/L Al,and there was little difference in radical respiration rate between Zhechun NO.2 soybean with 0 and 3 mmol / L Al.The decrease of root elongation may be related to the inhibion of mitochondrial respiration rate.4.The response of soybean root cell wall composition in different root segments accounted for the Al resistance mechanism.Content of pectin uronic acid,hemicellulose,cellulose as well as Al content in two root segments were investigated.Al content in cell wall of 0-10 mm root segments were significantly higher than those of 10-20 mm root segments, and more Al were found in both 0-10 and 10-20 root segments of Zhechun NO.3.The amount of pectin uronic acid,hemicellulose 2 and cellulose in 0-10 mm root segments increased observably in two cultivars with Al. However,the pectin uronic acid,hemicellulose 1,hemicellulose 2 and cellulose concentration in 10-20 mm root segments had no notable changes with 3 mmol/L Al.The present datas showed that the root tip is the primary target of Al toxicity and the importance of pectin concentration for Al binding to cell wall and Al accumulation in different root segments, implying that Al binding to cell wall represent an important pathway in the response of soybean root to Al toxicity.5.Al is a toxic metal that produce disturbances in plant antioxidant defences giving rise to oxidative stress.In this study,with four different Al treatment concentrations(0,20,40,60 mg/L Al³⁺),Zhechun No.2 and Zhechun No.3 were grown in aerated full-nutrient media of 1/100 under optimum conditions for 10d and 20d,in order to study the response of leaf reactive oxygen species(ROS)and antioxidant enzyme activities to Al toxicity.The main results showed that:compared with controls,leaf O₂·^-formation rate,OH·and H₂O₂ content of the two soybean cultivars increased under Al stress,with the lowest value occurred at 20 mg/ L.Meanwhile, significant increment in ROS accumulation was observed at 40mg/L Al³⁺, which was more serious along with increasing Al and extending time. 6.Mild stress promoted the SOD,POD,CAT and APX activities in this study,which enhanced scavenging capacity to DPPH free radicals,while keeped Al-induced ROS accumulation at a low range and avoided its damage,so as to increase Al adaptability of plants.However,high Al stress damaged defense system of ROS,whereas restricted antioxidant enzyme activities remarkably,runned up ROS production,augmented oxidative stress and membrane lipid peroxidative level,thus caused the activation and release of PPO.The enhancement of PPO activity accelerated phenolic compounds transforming to more toxic quinones,and finally did harm to Zhechun No.2 and Zhechun No.3.Combining with those conclusions,it can be inferred that Al aroused oxidative stress and growth inhibition in plants, but different plant genotypes with different antioxidant abilities differ in growth inhibition under Al stress.In the experiment,antioxidant enzyme activities were higher in Zhechun No.2 and ROS accumulation was much lower,thereby oxidative stress and lipid peroxidation were less seriouse.