The Preliminary Mechanism Of Potassium In Regulation Of Anthocyanins Metabolism In Hypocotyls Of Radish Sprouts

Potassium,a macroelement for plant growth and development,regulates plant physiological and biochemical processes by regulating enzyme activity,metabolite synthesis,signal transduction,stress and osmotic balance.Previous studies have shown that potassium can affect the accumulation of anthocyanins in plants,but the conclusions were inconsistent,and the molecular mechanisms involved have not been explored in detail.In this paper,we investigated the effects of potassium on the expression level of genes which related in anthocyanins biosynthesis,sugar metabolism and sugar signaling in hypocotyls of radish seedlings.’Yang Hua Radish’sprouts were used as experimental material to demonstrate the role of sucrose metabolism and signaling in the regulation of anthocyanins biosynthesis by potassium.The main results were as follows.1)The accumulation of anthocyanins was inhibited by potassium.Treating with different concentrations of KCl,the growth of radish sprouts was significantly promoted but the accumulation of anthocyanins was remarkably inhibited in the hypocotyls.The results of the anion interference test showed that the trend of anthocyanins content under Mg Cl₂ and Ca Cl₂ treatment was not consistent with KCl treatment,which proved that the K⁺rather than Cl^-affected the content of anthocyanins under KCl treatment.The results of the determination of endogenous potassium content in each tissue of the sprouts also showed that the accumulation of endogenous potassium in the hypocotyls was the most significant,and the content of endogenous potassium was negatively correlated with the change of anthocyanins content.The expression level of key genes involved in anthocyanins biosynthesis pathway was detected by Quantitative Real-time PCR.The expression of all structural genes except Rs4CL was lower under potassium treatments than potassium deficiency treatment,especially the late structural genes Rs DFR,Rs ANS and Rs GSTF12,further demonstrating that potassium can regulate anthocyanins metabolism.In addition,the detection of hypocotyls ROS levels revealed that the accumulation of anthocyanins under low potassium conditions was not mainly due to stress,thus further demonstrating that potassium inhibits anthocyanins accumulation.2)Sugar metabolism,phytohormone signaling transduction may beregulated by potassium.Transcriptomic analysis showed that the KEGG enrichment pathway was more enriched in Biosynthesis of secondary metabolites,Phenylalanine metabolism,Carbon metabolism,Flavonoid biosynthesis,Pentose phosphate pathway,Starch and sucrose metabolism,Plant hormone signal transduction and Nitrogen metabolism among the three treatments.These data suggested that sugar metabolism,hormone signaling transduction are possible pathways regulated by potassium.3)The activity of Rs ANS promoter was repressed by Rs MYB82,the activity of Rs GSTF12 promoter was activated by Rs MYB39.Trend analysis of transcriptome data revealed that potassium could activate the expression of R2R3 MYB repressor factor Rs MYB82 and inhibit the expression of R2R3 MYB activator Rs MYB39.Yeast one-hybrid assays,GUS activity analysis,and dual-luciferase assays demonstrated that Rs MYB82 could inhibit the promoter activity of Rs ANS,and Rs MYB39 could interact with the promoter of Rs GSTF12 to activate its activity,which participated in the metabolic of anthocyanins through an activation-inhibition network under potassium treatments.4)Sucrose affects the regulation of potassium on anthocyanins in radish sprouts hypocotyls through metabolism and signal transduction pathways.The determination of the content of sugars in hypocotyls under different concentrations of potassium showed that the content of soluble total sugar and sucrose showed a consistent change trend with the content of anthocyanins,that is,it decreased with the increase of potassium ion concentrations.The expression levels of Rs MYB82 and Rs MYB39 in potassium treatments alone and potassium plus sucrose treatments revealed that the expression level of these gene were inconsistent with the previous results,suggesting that sucrose did not regulate the accumulation of anthocyanins through these two transcription factors.The expression levels of genes involved in sucrose metabolism and signal transduction pathway were determined between different potassium concentrations,and the expression of sucrose degradation-related genes Rs SUS1L,Rs VIN1 and hexose kinase Rs FRK1 increased with increasing potassium ion concentrations,while sucrose transporter gene Rs SUC2 and monosaccharide efflux gene Rs SWEET12L were inhibited by potassium.It has been proved by exogenous addition of sucrose and exogenous sugar signal inhibition experiments,the levels of anthocyanins were significantly increased between different potassium ion treatments with sucrose and sugar signaling inhibitors,and there was no significantly difference between the three potassium concentrations.When sucrose and sugar signaling inhibitors were added on the basis of normal potassium treatment as control,the expression level of MYB activator Rs MYB75 was significantly up-regulated,and the expression level of Rs MYB75 in the treatment with sugar inhibitor was lower than that in the treatment with sugar.The expression level of the above sugar pathway-related genes were also significantly lower under the sugar signaling inhibitor treatment than that under the sucrose treatment,but significantly higher than that under the potassium treatment alone.These results suggested that sucrose may regulated of potassium on anthocyanins metabolism in hypocotyls of radish sprouts through metabolism and signal transduction pathways.