胡杨对叶锈菌侵染的生理响应

Physiological responses of Populus euphratica to leaf rust infection

胡杨叶锈病是严重危害胡杨幼苗、幼林的真菌病害之一,对胡杨(Populus euphratica)人工林造成影响,目前国内外鲜有对胡杨感染叶锈菌松杨栅锈菌(Melampsora larici-populina)后生理响应的报道。本研究以胡杨为材料,喷施松杨栅锈菌,对照喷施蒸馏水,在感染7、14和21 d后取感病叶片和对照叶片,测定叶片活性氧(ROS)含量、抗氧化酶活性、激素和酚类等物质含量的变化,以探究胡杨对叶锈菌的防御机制。结果表明:(1)随着胡杨感病时间增加,ROS含量在感病叶片中下降;感病叶片中硝酸还原酶(NR)活性在14d时上升至133.91 mU·g^(-1),且活性均高于未感病植株;超氧化物歧化酶(SOD)、过氧化物酶(POD)、过氧化氢酶(CAT)及抗坏血酸过氧化物酶(APX)活性在感病后都有不同程度的升高,其中POD和APX活性在感病21 d时比未感病植株分别提高87%和1.17倍,且NR活性在感病后与POD正相关性增强。(2)叶片中脱落酸(ABA)和水杨酸(SA)含量在感病后增加,在感病14 d时的叶片中分别达到463.63 ng·g^(-1)和39.51μg·g^(-1)。(3)感病叶片中肉桂酸-4-羟化酶(C4H)和无色花色素还原酶(LAR)活性在14 d时分别在达到1.31 kU·g^(-1)·min^(-1)和54.70 U·g^(-1)·min^(-1)后下调;总酚和黄烷醇含量变化趋势一致,在14 d时分别在降低至2.18 mg·g^(-1)和90μg·g^(-1)后上升,且总酚和黄烷醇含量呈显著正相关。胡杨通过提高抗氧化酶活性清除ROS以提高对病原菌的防御能力;ABA和SA在感病叶片中发挥防御作用并与抗氧化酶活性的提高密切相关,且可能连同NR介导的NO信号途径共同调控植物对病菌的防御过程;苯丙烷途径产生的次级代谢物总酚、黄烷醇等也在防御过程中发挥重要作用。本研究为胡杨对叶锈菌侵染的防御机制研究提供参考。

Populus euphratica leaf rust,caused by Melampsora larici-populina,is one of the serious fungal diseases that damages poplar seedlings and young forests,which also affects P.euphratica afforestation.However,very few reports have studied how P.euphratica physiologically responds to M.larici-populina infection.We used P.euphratica as the experimental material.We sprayed poplar with M.larici-populina exogenously,while we sprayed the control with distilled water.Subsequently,we collected the infected and control leaves at 7,14,and 21 d post-infection,and we aimed to explore the defense mechanism of P.euphratica against the leaf rust fungus by investigating the changes in the leaf reactive oxygen species(ROS),antioxidant enzymes,hormones,and secondary metabolites like phenol and flavanol.The results show:(1)The ROS content decreased in the infected leaves.Nitrate reductase(NR)activity in infected leaves increased to 133.91 mU·g^(-1)at 14 d,with the NR activity in the infected leaves being higher than that of the control.As compared with control,the activities of superoxide dismutase(SOD),peroxidase(POD),catalase(CAT),and ascorbate peroxidase(APX)all increased,with POD and APX activities increased 87%and 1.17 times at 21 d,respectively.Furthermore,the positive correlation between activities of NR and POD had increased post-infection.(2)Infected leaves had higher abscisic acid(ABA)and salicylic acid(SA)contents than the control post-infection,which reached 463.63 ng·g^(-1)and 39.51μg·g^(-1)at 14 d in the infected leaves.(3)The activities of cinnamate 4-hydroxylase(C4H)and leucoanthocyanidin reductase(LAR)reached 1.31 kU·g^(-1)·min^(-1)and 54.70 U·g^(-1)·min^(-1)in the infected leaves at 14 d.The trend changes of phenol and flavanol were similar,and they decreased to 2.18 mg·g^(-1)and 90μg·g^(-1)at 14 d,respectively,and subsequently increased.We found a significant positive correlation between phenol and flavanol contents.In conclusion,P.euphratica scavenged ROS by enhancing antioxidant enzyme activity to improve the disease resistance in infected leaves.The plant hormones ABA and SA played defensive roles in infected leaves and were related to the enhancement of antioxidant enzyme activities.Furthermore,the NR-mediated nitric oxide signal pathway may participate in plant defense against pathogens along with hormones.The secondary metabolites produced by the phenylpropane pathway,like total phenol and flavanol,also were essential in poplar defense.Therefore,we provided a reference for future studies focused on the defense mechanism of P.euphratica against the M.larici-populina fungus.