Study On The Response Mechanism Of Ottelia Acuminata To Different Level Of Nutrition And Heavy Metal Stress

Eutrophication and heavy metal pollution have become serious water quality problems,which will cause changes in water environment and aquatic ecosystem functions worldwide.Aquatic plants are one of the important components of aquatic ecosystem and play an important role in purifying water quality and maintaining the stability of aquatic ecology.Therefore,exploring the physiological and molecular mechanisms of the effects of heavy metals and eutrophication on aquatic plants can not only provide a scientific theoretical basis for the protection and management of aquatic plants and the restoration of eutrophication lakes,but also provide a reference and theoretical basis for the study of aquatic plants response to climate change.The Ottelia acuminata is endemic aquatic plant in southwest China and is indicator species to predict water pollution.Under oligotrophic and eutrophic conditions,physiological and biochemical parameters and transcriptome were analyzed to explore the mechanism response to Cr⁶⁺and N,P stress of Ottelia acuminata.The study will provide a theoretical basis for the population recovery of Ottelia acuminata in plateau lakes,provide a new idea for the recovery and ecological management of aquatic ecosystem in plateau lakes.The main results and conclusions are as follows:（1）The physiological indicators of photosynthetic electron transfer rate（ETR）,photosystem actual photosynthetic efficiency（YⅡ）and photochemical quenching coefficient（q P）of chlorophylls significantly decreased under low N and P treatments of Ottelia acuminata,indicating that the PSII structure might be damaged under low N、P treatments.In the high N and P treatments,the proline（Pro）content of Ottelia acuminata significantly increased with the increase of treatment time;the contents of chlorophyll a,chlorophyll b and carotenoid decreased with increase of treatment time;the Fv/Fm and Y（NPQ）significantly decreased,as well as the Y（NO）significantly increased with the increase of treatment time.（2）Under the oligotrophic condition,the contents of ETR,YⅡand q P of Ottelia acuminata were significantly decreased under with Cr⁶⁺（Cr＿OC）and without Cr⁶⁺（control＿OC）,and the content of q P was lower in Cr＿OC.This indicated that the light energy conversion efficiency may be reduced under the oligotrophic condition of Ottelia acuminata,and the PSII structure may be damaged.Under eutrophic condition,the proline content of Ottelia acuminata with Cr⁶⁺（Cr＿EC）and without Cr⁶⁺（control＿EC）significantly increased with the increase of treatment time;the contents of total chlorophyll,chlorophyll a and carotenoid significantly decreased with the increase of time;Fv/Fm significantly decreased in control＿EC;Y（NPQ）significantly decreases with the increase of time,and Y（NPQ）has low value in Cr＿EC stress;Y（NO）significantly increased with the increase of time.（3）The differential expression of genes（DEGs）and the weighted gene co-expression network analysis（WGCNA）of Ottelia acuminata under Cr⁶⁺and N and P stress showed that the pathway of energy metabolism,carbohydrate metabolism,secondary metabolism and amino acid metabolism were enriched.The genes involved in photosynthesis,lignin synthesis pathway,and DNA damage were inhibited under Cr⁶⁺stress of Ottelia acuminata.Under eutrophication,the genes involved in light-capture proteinwere low expression level;under high N and low P conditions,the genes involved in chlorophyll and carotenoid synthesis were high expression levels;the genes involved in electron transport process were high expression levels under high N and P conditions.Meanwhile,the expression of genes involved in pectin degradation and lignin synthesis pathway were affected by eutrophication,suggesting that cell wall plays an important role in response to eutrophication of Ottelia acuminata.Based on physiological and biochemical indicators and transcriptome,this study revealed the mechanism of growth and molecular response to Cr⁶⁺,N and P stress of Ottelia acuminata.It can provide a new idea for the protection and population recovery of Ottelia acuminata.