Physiological And Biochemical Characteristics And Molecular Mechanisms Of Willow In Response To Cobalt Stress

For plants,cobalt is a non-essential heavy metal element,which promotes the growth and development of plants in an appropriate amount.However,when plants absorb too much cobalt from the soil,it will have harmful effects on plants.At present,the research on the mechanism of cobalt stress response of plants mainly focuses on economic crops or herbaceous model species,while the research on the response mechanism of cobalt stress in woody plants was relatively rare.In this paper,the Salix babylonica was used as experimental materials to study the molecular response mechanism of willow to cobalt stress and reveal the physiological and biochemical characteristics of willow response to cobalt stress and the underlying molecular mechanism by combining the results of morphological,physiological and biochemical indicators with transcriptome data and microRNA sequencing.The main results of this paper are as follows:1.In terms of morphology,100 ?M cobalt stress caused leaf chlorosis and inhibited the growth of roots,resulting in obvious phenotypic changes in the willow.At physiological and biochemical levels,cobalt stress caused a large accumulation of cobalt in the plant,affecting the content of other metal elements in the body,and significantly reducing the content of chlorophyll a and chlorophyll b in the leaves of plants.Cobalt stress significantly changed the stomatal conductance of the leaves,increased the transpiration rate and intercellular carbon dioxide content,but the net photosynthetic rate decreased significantly,and the total soluble sugar content in the plants increased significantly.Cobalt stress induced oxidative stress in willow,which results in the accumulation of reactive oxygen species(ROS)in root.The activities of peroxidase(POD)and superoxide dismutase(SOD)increased significantly,while the activity of catalase(CAT)decreased.The oxidative stress damaged the plant roots,causing a significant increase in malondialdehyde(MDA)content in the roots.2.At the molecular level,1165 differentially expressed genes and 62 differentially expressed microRNAs were found in the roots of the plants by RNA-seq analysis.836 differentially expressed genes and 80 differentially expressed microRNAs were found in the tops.Pathway enrichment analysis revealed that these differentially expressed genes and microRNAs were mainly involved in carbohydrate metabolism,lignin metabolism,amino acid metabolism and flavonoid metabolism.3.Three possible defense mechanisms of willow in response to cobalt stress were proposed in this paper:First,to drain and reduce the absorption of cobalt ions in order to reduce their content in plants by secreting a large number of organic acids from roots and regulating the expression of a series of metal ion transporter genes;Second,removing ROS and free radicals induced by cobalt stress in plants by regulating the expression of a series of antioxidant system genes,enhancing the activity of antioxidant enzymes and the content of antioxidants;Thirdly,to reduce the free cobalt ions in plant cells by complexing and chelating excessive cobalt ions with cysteine-rich phytochelatins(PCs)or metal lothioneins(MTs).4.In response to cobalt stress,the content of citric acid in the roots of the plants increased significantly.In the tricarboxylic acid cycle(TCA),Aconitase(ACO),which catalyzes the synthesis and accumulation of citric acid reversibly and has the function of iron ion homeostasis regulation,also has up-regulated gene expression.Aconitase had undergone gene expansion in angiosperms,and large fragments duplication contributed to the expansion of the gene family.After gene expansion,two major gene clusters of A1 and A2 were produced,and their gene structure,molecular selection pressure and expression pattern analysis showed that the genes on the A2 branch were under more stronger selection constraints and their gene structure were more conservative and had higher expression levels in the root.In summary,this paper studied the effects of cobalt stress on the physiological and biochemical levels of woody plants,and revealed the underlying molecular mechanism.Through the transcriptome and microRNA analysis,three defense mechanisms of willow response to cobalt stress were discovered.The results of this study provided a theoretical reference for the response mechanism of woody plants to cobalt stress from a comprehensive perspective,and provided a theoretical basis for the cultivation of new forest varieties with higher resistance.