Effects Of Endophytic Fungi Infection On Photosynthetic Characteristics And Carbon And Nitrogen Metabolism Of Rice Seedlings Under Aluminum And/or Cadmium Stress

Aluminum and heavy metal cadmium in acid soil can harm the growth of plants and affect the yield and quality of crops.Rice is an important food crop in China,which is increasingly polluted by aluminum and cadmium.Therefore,it is important to study how to alleviate the toxic effects of aluminum and cadmium on rice.In this study,rice seeds of Liaoxing 1 were used as the research material,and the changes of seedling growth indexes,photosynthetic indexes,carbon metabolism,nitrogen metabolism related substances and enzyme activities in leaves and roots were measured under CK（0μM）,Al（80μM）,Cd（50μM）and Al+Cd（80μM Al+50μM Cd）stress by endophytic fungi Gao Y1-1 of Suaeda salsa.Experiments were carried out to explore the alleviating effect of endophytic fungi Gao Y1-1 on the growth of rice seedlings under single and combined stresses of Al and Cd.Research results showed:1.Under single and combined stresses of Al and Cd,the plant height,root length and above ground dry weight of rice seedlings were significantly reduced,while the under ground dry weight was increased.The infection of endophytes increased the height of seedlings,the accumulation of dry matter in the above ground and the under ground.2.Under single and combined stresses of Al and Cd,the chlorophyll content,net photosynthetic rate（Pn）,stomatal conductance（Gs）,intercellular carbon dioxide concentration（Ci）,transpiration rate（Tr）,maximum photochemical efficiency of photosystemⅡ（Fv/Fm）and potential activity of photosystem II（Fv/F₀）of rice seedlings decreased.The chlorophyll content,Pn,Gs,Tr,Fv/Fm and Fv/F₀ of leaves were increased after endophyte infection,but Ci was decreased.3.Under single and combined stresses of Al and Cd,the carbon metabolism-related substances and SPS activity in the leaves and roots of rice seedlings were increased,while the activities of SS and amylase were decreased,and the changes of invertase activities were not obvious.The infection of endophytes can improve the sucrose content,SPS activity and amylase activity in leaves and roots of rice seedlings to some extent;reduce starch content and SS activity in leaves and roots;improve the soluble sugar content and invertase activity of leaves;reduce the roots soluble sugar content and invertase activity.4.Under single and combined stresses of Al and Cd,the contents of nitrate nitrogen and free amino acids in the leaves and roots of rice seedlings decreased,the content of soluble protein increased,and the activity of nitrate reductase（NR）in leaves decreased.The leaf ammonium nitrogen content and glutamate synthetase（GOGAT）activity decreased,while the activities of glutamine synthetase（GS）and glutamate dehydrogenase（GDH）were increased;the root system had the opposite change.The inoculation of endophytes can reduce the nitrate nitrogen content in the leaves and roots of the seedlings and the ammonium nitrogen content in the leaves;increase the soluble protein,free amino acid content,NR,GS,GOGAT,GDH activities,and root ammonium nitrogen in the leaves and roots content.In conclusion,endophytes can improve the photosynthetic characteristics of rice seedlings,change the activities of carbon and nitrogen metabolism-related enzymes,promote the synthesis and transportation of carbohydrate and nitrogen metabolism-related substances,enhance the tolerance of rice to Al and Cd,and promote the growth of rice seedlings.