Study On The Physiology Of Ionic Interaction On Ricinus Communis L. And The Molecular Mechanism Of Phosphorus On Its Tolerance To Copper

Soil heavy metal pollution is often not caused by a single element pollutant,but by a variety of heavy metal such as cadmium?Cd?and copper?Cu?pollutants and their interactions.The interactions within the elements of heavy metal compound pollution,as well as between them and the plant's essential nutrients,have a conspicuous impact on the growth of plants,and considerably distinguish from that of a single heavy metal.Moreover,the relevant studies mainly focus on the physiological and biochemical level,lacking of deep molecular mechanisms.As a commonly used agronomic practice,applying phosphorus?P?fertilizer is frequently used as an effective strategy to enhance plant tolerance to heavy metal and detoxification.The Ricinus communis L.?R.communis?were used as candidate objects for this study.The hydroponic experiments were conducted to investigate the effect of ion interaction on the growth and physiology of R.communis under Cu stress,unveiling the physiological characteristics of R.communis under multi-media system.The transcriptome sequencing was used to illustrate the transcriptional regulation of the response of R.communis to Cu stress alone with the role of P in enhancing the tolerance to Cu,uncovering the potential molecular mechanism.The relevant results are as follows:?1?A hydroponic experiment was carried out to study the influence of interaction between Cu and Cd on the growth and physiology of R.communis.The results showed that the strongest inhibition to R.communis of the single and combined pollution of Cu and Cd occurs at the complex effect of high concentration of both Cu and Cd,followed by single Cd pollution.Cd stress can inhibit the growth of R.communis,reduce root morphological parameters?e.g.root length,root surface area,root volume and root average diameter?,decrease photosynthetic pigments contents and induce oxidative stress and stimulate a certain response to oxidative stress.The effect of Cu includes two dimensions.Specifically,the low concentration of Cu can improve the growth of R.communis and alleviate the toxicity of low concentration of Cd on R.communis by stimulating the antioxidant defense system,indicating an antagonistic effect with Cd;however,the high concentration Cu can pose a toxic effect on R.communis and aggravate the Cd stress,suggesting a synergistic effect with Cd.?2?A hydroponic experiment was conducted to study the influence of interaction between Cu and Ca on the growth and physiology of R.communis.The results showed that Cu stress significantly decreased the fresh weight,relative growth rate and photosynthetic pigments contents of R.communis;It also results in inhibition of root growth and imbalance of nutrients absorption.Additionally,Cu stress increased MDA and H₂O₂ contents as well as antioxidant enzyme activity and nonenzymatic antioxidants contents in leaves of R.communis.The Low concentration of Ca?5 mmol/L?showed a certain antagonism with Cu and improved the growth of R.communis and inhibited the uptake of Cu by R.communis via alleviating the inhibition effect of Cu on plants.Specifically,the low concentration of Ca increased the various root morphological parameters and photosynthetic pigments contents,and also significantly reduced the antioxidant enzyme activity and non-enzymatic antioxidant contents to maintain them at an equal level to that of the control.However,the excess Ca may also cause toxicity to R.communis.?3?The transcriptome sequencing was used to analyze the expression changes of root of R.communis in response to Cu stress.The results showed that a total of 51299transcripts were assembled and the annotation rate of unigenes was up basically to 80%.Compared with CK,Cu stress obtained totally 3783 differentially expressed genes,including 1551 up-regulated genes and 2232 down-regulated genes;these differentially expressed genes mainly involved in phenylpropane metabolism,hydrogen peroxide decomposition,reactive oxygen metabolism,oxidoreductase activity,hormone signal transduction,glutathione metabolism and other processes and pathways.Compared with no P addition,the application of P gained a total of 160 differentially expressed genes,of which 102 were up-regulated and 58 were down-regulated,respectively;these differentially expressed genes mainly involved in the response to oxidative stress,the binding,precipitation and transport of Fe,oxidoreductase activity,various amino acid metabolism and other biological processes.In conclusion,these findings reveal the physiological response of R.communis in multi-media systems and the molecular mechanisms of R.communis in response to Cu stress as well as that of P to enhance its resistance to Cu.Additionally,it provides inspiring understanding on biological adaptation and resistance mechanism of R.communis to sophisticated systems and broad prospects for the application of R.communis.