Studies On The Photosynthetic Physiology And Molecular Mechanisms Of Poplar Infected By Canker Diseases

Canker diseases of poplar are the main disease that restricts the development of poplar plantation.The studies showed that the photosynthesis of poplar could be inhibited after the occurrence of canker diseases.However,the physiological and molecular mechanisms by which these diseases inhibit photosynthesis in poplar remain unclear.Taking P.bolleana-pathogenic fungi as the experimental system,this study analyzed the effects of pathogen stress on photosynthetic characteristics,chlorophyll fluorescence characteristics,stomatal characteristics,water and carbon metabolism,hormone levels and gene expression in leaves of P.bolleana,and analyzed the specific physiological and molecular mechanisms of canker disease affecting photosynthetic carbon assimilation in leaves of host plants.The main results are as follows:（1）The net photosynthetic rate（P_n）,stomatal conductance（G_s）and chlorophyll fluorescence parameters of P.bolleana leaves significantly decreased at the early stage of the stress of B.dothidea and V.sordida.Stomatal restriction analysis showed that the decrease of P_nunder the stress of V.sordida was mainly caused by non-stomatal factors,while the decrease of P_nunder the stress of B.dothidea was mainly caused by stomatal factors,indicating that the restriction pathways of photosynthesis of P.bolleana under the early stress of the two pathogenic fungi were different.（2）In this experiment,the stomatal conductance,transpiration rate（Tr）and water use efficiency（WUE）of P.bolleana leaves significantly decreased under the stress of V.sordida,and the water vapor pressure deficit significantly increased,while the petiole water potential was basically unchanged,indicating that V.sordida only affected the water use of P.bolleana leaves,but did not cause the deterioration of water condition of leaves.The results of non-structural carbohydrate（NSC）content showed that the NSC of the leaves increased under pathogenic stress,while the NSC of the roots significantly decreased.It may be related to the functional damage of phloem caused by the infection of V.sordida,which hinders the transport of NSC from the leaf tissues to the root.（3）The analysis of leaf transcriptome data showed that the expression of disease-resistant protein synthesis,epigenetic modification,RNA variable shear and other related genes in P.bolleana leaves were down-regulated under the stress of V.sordida,and the expression of genes related to oxidative phosphorylation pathway was significantly up-regulated,while the expression of genes related to photosynthesis was not affected.（4）At the early stage of B.dothidea stress,the decrease of net photosynthetic rate of P.bolleana leaves was mainly caused by stomatal factors,and then changed to non-stomatal factors.The decrease of chlorophyll content and chlorophyll fluorescence parameters indicated that the main reasons for the decrease of P_nin P.bolleana leaves were the inhibition of light absorption and transformation,and electron transfer.In addition,it was found that ABA,Me JA and H₂O₂in P.bolleana leaf tissues did not increase in the early stage of B.dothidea stress,while stomatal openness significantly decreased,indicating that the stomatal closure caused by pathogen stress was unrelated to hormones.