Responses Of Alternaria Alternata To Oxidative Stress And Its Possible Mechanisms Invoved

Reactive oxygen species(ROS)burst and changes in intracellular redox balance play an important regulatory role in plant-pathogen interactions.Successfully deoxidating higher level of ROS produced by the host is required for further infection of plant pathogens.In order to reveal the mechanism underlying pathogens responding to oxidative stress,effect of high-level H₂O₂ stress on growth,cellular ROS production and antioxidant system(As A-GSH cycle and thioredoxin system)related enzyme activity and gene expression,antioxidant content of Alternaria alternata were studied based on comparative analysis of its tolerance tooxidative stress using in vitro test system.The results show:1.Trichothecium roseum,Fusarium sulphureum,Penicilium expansum and A.alternata were all tolerant to exogenous H₂O₂ oxidative stress,and their tolerant capacities varied with pathogenic fungi species.Under more than 30 m M H₂O₂stress,four pathogenic fungi still growth after 3d incubation.Among them,the mycelium diameter of A.alternata was the largest.2.Exogenous low concentrations of H₂O₂(0?10 m M)increasedthe intracellular ROS production in A.alternata,while exogenous high concentrations of H₂O₂(30?50 m M)stimulated ROS scavenging ability of A.alternata.At 30 and 50 m M H₂O₂oxidative stress,the H₂O₂ content in A.alternata culture medium was decreased by 27.4%and 37.4%,respectively compared to the control after 4 h incubation.3.Exogenous 30 m M H₂O₂ stress treatment significantly promoted O₂^·-production rate and H₂O₂ accumulation in A.alternata at the early stage.2 h after treatment,the intracellular O₂^·-production rate and H₂O₂content in oxidative stress group were increased by 22.9% and 41.4%,respectively compared to the control,and then gradually decreased.At the same time,the gene expression level and activity of A.alternata NOX were also significantly induced after exogenous 30 m M H₂O₂ treatment.NOX enzyme activity peaked at 2 h after treatmrmt,which was increased by 18.9%compared with the control group.4.Upon responding to exogenous H₂O₂stress,the activities of antioxidant enzymes SOD,CAT and POD and gene expression level of A.alternata increased significantly,the SOD and POD activities peaked at 2 h,which was 33%and 52.6%higher than the control group,respectively;the activities of GR,GPX,APX and MDHAR in the As A-GSH system were significantly induced,and the contents of antioxidants such as GSH,As A and DHA,and GSH/GSSG ratio were also significantly increased.DHAR and GST enzyme activities are reduced.Meanwhile,the Trx content in the A.alternata thioredoxin system increased.The activity of Trx R and its gene expression were also significantly induced after oxidative stress.In addition,the G6PDH enzyme activity and gene expression of A.alternata were also significantly increased under oxidative stress.In summary,A.alternata can rapidly respond to exogenous H₂O₂ oxidative stress and initiate antioxidant mechanisms such as intracellular reactive oxygen scavenging system(As A-GSH cycle and thioredoxin system)to maintain intracellular redox balance,and further start the normal infection process.