Al Stress On Root Tipantioxidant System Of Two Eucalyptus Seedlings Under H₂O₂ Pretreatment

Eucalyptus,native to Australia,is a large evergreen tree of Eucalyptus in mytaceae.Eucalyptus has become an ideal tree species for landscaping and economic afforestation because of its tall and beautiful shape,evergreen,low maintenance cost,barren resistance,fast growth rate and good material quality,which plays an important role in regional economy and environmental management.The main Eucalyptus growing areas in China are mainly distributed in South China and southwest China.About half of the world’s potential arable soil p H is below 5.5.Aluminum toxicity is one of the main factors affecting plant growth,and root tip is the initial site of plant stress.In this study,two different Eucalyptus species（Eucalyptus urophylla×E.grandis and Eucalyptus Pellita）were used to study the effects of 0.2 m M H₂O₂pretreatment on ROS metabolism and antioxidant system under Al³⁺（120 mg/L）stress.It provides scientific basis for the protection,development and utilization of Eucalyptus Plantation and the protection of germplasm resources on acid soil in South China.The main conclusions are as follows:1.Under 24h Al³⁺（120 mg/L）stress,the growth of Eucalyptus urophylla and Eucalyptus urophylla were inhibited in different degrees,and the relative root elongation of Eucalyptus urophylla seedlings in hydroponics was significantly lower than that of Eucalyptus urophylla×E.grandis.2.The results showed that 0.2 m M H₂O₂pretreatment could alleviate the stress of Al³⁺（120 mg/L）treatment on Eucalyptus roots,and the relative root elongation was higher than that of other concentrations of H₂O₂,and the root activity was enhanced.3.Under 0.2 m M hydrogen peroxide pretreatment,the H₂O₂Content,O₂^-content,MDA content and Evans blue absorption of water culture root tips of Eucalyptus urophylla×E.grandis and Eucalyptus pellita were significantly lower than those of non-H₂O₂pretreatment group,indicating that exogenous H₂O₂pretreatment can reduce the above indexes of root tips of Eucalyptus urophylla×E.grandis and Eucalyptus pellita under Al stress,and maintain their membrane lipid peroxidation and cell membrane integrity.4.The activities of cat,APX,pod,SOD,GR,GPX,MDHAR and DHAR in water culture root tips of Eucalyptus urophylla×E.grandis and Eucalyptus pellita under 0.2 m M hydrogen peroxide pretreatment were increased in varying degrees.It indicated that under the addition of exogenous H₂O₂,Eucalyptus urophylla×E.grandis and Eucalyptus pellita showed a high level of antioxidant enzyme activity to resist stress.5.In the As A GSH cycle,there were no significant differences in the total ascorbic acid（TAs A）,dehydroascorbic acid（DHA）and reduced/total ascorbic acid ratio between Eucalyptus urophylla×E.grandis and Eucalyptus pellita among the treatment groups（including the control）;at the same time,the GSSG of Eucalyptus urophylla×E.grandis root tip under aluminum stress was not significantly different The content and GSH/GSSG ratio of Eucalyptus pellita root tip were significantly increased compared with the control group,but the GSSG content of Eucalyptus pellita under Al stress was significantly lower than that of the control.Under 0.2 m M hydrogen peroxide pretreatment,the root tip ASA content of Eucalyptus urophylla×E.grandis and Eucalyptus pellita and GSH/GSSG ratio of Eucalyptus pellita in Al treatment group were significantly higher than those in single Al treatment group（without H₂O₂pretreatment）.6.In this experiment,it was found that the DPPH and FRAP of Eucalyptus urophylla×E.grandis and Eucalyptus pellita were significantly higher than those of the control group after Al³⁺（120 mg/L）treatment,and the DPPH and FRAP of E.urophylla were significantly higher than those of Eucalyptus pellita,It showed that the resistance of Eucalyptus urophylla×E.grandis to aluminum stress was stronger than that of Eucalyptus pellita.The principal component scores of each treatment also showed that Eucalyptus urophylla×E.grandis had stronger resistance to aluminum stress,and the effect of 0.2 m M H₂O₂ concentration on alleviating Al stress was more significant.