Responses Of Myriophyllum Spicatum To Salt Stress And Its Salt Tolerance Mechanism

Myriophyllum spicatum is a submerged plant widely found in rivers and lakes.Due to its strong absorption capacity and rapid reproduction,it is often used as a pioneer species in ecological restoration of waters.In recent years,both indoor research and field investigations have shown that the submerged plants have potential salt-tolerant properties,while salt tolerance and mechanisms are rarely studied.In this paper,M.spicatum was studied.According to the salt-tolerance characteristics of M.spicatum,the characteristics of plant growth and change,photosynthetic and respiratory life processes,physiological mechanism response and transcriptome regulation were analyzed to understand the salt stress response of M.spicatum.The specific results are as follows:1.The effect of salinity,temperature and light on the growth of M.spicatum: The0~12 salinity group had a higher specific growth rate.In the 15 salinity group,the fresh weight,plant height and leaf number of M.spicatum were significantly lower than those of other salinity groups.2.Effects of salt stress on photosynthesis of M.spicatum: Salinity stress treatment for 10 days,photosynthetic indexes such as Fo,Fm,Fv / Fm,Fv'/Fm',and YII increased with increasing salt concentration.From day 15,the photosynthesis of the 12 salinity group and the 15 salinity group gradually weakened.On the 20 th day,the photosynthesis of the 9 salinity group was weakened.Until the end of the experiment on the 25 th day,photosynthetic indexes such as Fo,Fm,Fv / Fm,Fv'/Fm',and YII decreased as the salt concentration increased.During the salt stress,the photosynthesis of the 3 and 6 salinity groups was slightly higher than that of the 0 salinity group.3.Physiological response of low salinity stress of M.spicatum: During the 25 days of the experiment,the malondialdehyde(MDA)content increased with increasing salinity.The small molecular organic proline(PRO)and soluble sugar involved in osmotic adjustment increased with increasing salinity.Antioxidant activity enzymes involved in antioxidant defense,superoxide dismutase(SOD),catalase(CAT),peroxidase(POD),showed an increase with salinity on the 5th day of stress.Theactivity was enhanced,and in the monitoring on the 15 th day and the 25 th day,both the12 salinity group and the 15 salinity group showed a decrease.4.Transcriptome analysis of low salinity stress of M.spicatum: Set the salinity gradient to 0 salinity group control,6 salinity and 12 salinity.6 Salinity and 12 salinity were compared with the 0 salinity control group respectively,and the catalytic activity and the number of up-regulated genes in the molecular function were the highest.The number of up-regulated genes in catalytic activity of the molecular function are the most.Among the cell components,the cell membrane and cell membrane components were up-regulated most.The up-regulation of cellular processes and metabolic processes in biological processes is most expressed.The results of KEGG enrichment analysis showed that carotenoid biosynthesis was the most concentrated in the up-regulated genes,and Unigene was the most abundant in starch and sucrose metabolism.The photosynthesis-antenna protein in the down-regulated gene has the largest degree of enrichment and the largest number of genes,followed by the highest number of genes for plant hormone signal transduction.In summary,under the salt stress condition,the highest salinity tolerated by M.spicatum was 12,showing a good growth state at 3 salinity and 6 salinity.When it is subjected to salt stress,it increases the chlorophyll content to enhance photosynthesis ability,secretes small organic molecules to regulate cell membrane permeability,and increases the activity of antioxidant enzymes against oxidative stress damage,for corresponding to salt stress.At the same time,at the level of transcriptome,normal metabolism and growth of tissues are ensured by up-regulating catalytic activity and binding genes.In this study,the salt tolerance mechanism of M.spicatum was initially identified from the phenotype,photosynthesis,physiological response and transcriptome level,which provided a theoretical basis for salt tolerance breeding and ecological restoration of low salinity waters.