Sodium Silicate Treatment Promotes Wound Healing Of Harvested Muskmelons And Its Related Mechanisms

Silicon is ranked second most abundant among the most elements prevalent in the Earth’s surface,also exists as amorphous and soluble silicon in plants.Although it is not an essential nutrient in plants,silicon induces resistance against biotic and abiotic stress by directly inhibiting pathogens,forming physical barriers,and inducing the synthesis of defense compounds.However,it has not been reported that the effect of sodium silicate on wound healing of muskmelon.In this study,wounded‘Manao’fruit was soaked in 50 mmol/L sodium silicate.The effects of sodium silicate treatment on wound healing of harvested muskmelon were evaluated.Based on the transcriptome analysis,the effects of sodium silicate treatment on glucose metabolism,fatty acid metabolism,and phenylpropanoid pathway at fruit wounds.Below are key research findings:1.Sodium silicate treatment reduced weight loss by wounded fruit,and disease index in fruit subjected to Trichothecium roseum.Sodium silicate accelerated deposition of suberin poly phenolic（SPP）,suberin poly aliphatic（SPA）,lignin and silicon layer,increased the thicknesses of SPP,SPA,lignin,and cell layers,silicon layer,silicon relative content,maintained the morphology in healing tissues.Sodium silicate treatment increased brightness,decreased a*and b*,increased the hardness and brittleness and reduced their resilience of the healing tissues at fruit wounds.2.Transcriptome sequencing showed that the number of DEGs between Control 1 d and Control 0 d was 4576,including 2521 upregulated genes and 2055 downregulated genes.In addition,there were 720 DEGs between Si 1 d and Control 1 d,of which259 genes were upregulated and 461 genes were downregulated.Transcriptome sequencing of sodium silicate fruit wound tissues through GO（Gene ontology）functional enrichment analysis showed that fatty acid biosynthesis and fatty acid metabolism in biological processes contributed significantly.KEGG（Kyoto encyclopedia of genes and genomes）metabolic pathway enrichment analysis,plant hormone signal transduction,plant-pathogen interaction and phenylpropane biosynthesis contributed significantly.In addition,we also found out that starch and sucrose metabolism,glycolysis/gluconeogenesis,fatty acid degradation,and pentose phosphate pathway with wound healing of fruit.3.Sodium silicate treatment increased activities of sucrose phosphate synthase（SPS）,sucrose synthase-synthesis（SS）,acid invertase（AI）and neutral invertase（NI）,decreased contents of sucrose,fructose and glucose,and increased activities of hexokinase（HK）,pyruvate kinase（PK）,and contents of adenosine triphosphate disodium（ATP）,adenosine diphosphate（ADP）and energy charge（EC）duiring wound healing.Besides,sodium silicate increased glucose-6-phosphate dehydrogenase（G-6-PDH）and 6-phosphogluconic dehydrogenase（6-PGDH）activities and nicotinamide adenine dinucleotide phosphate（NADP）and triphosphopyridine nucleotide（NADPH）contents at wound sites of muskmelon.4.For fatty acid metabolism,sodium silicate treatment up-regulated phospholipase A₂（PLA₂）gene expression and activity at fruit wounds during healing,enhanced contents of oleic acid,linoleic acid,linolenic acid and unsaturation degree of fatty acids,decreased palmitic acid and stearic acid.Sodium silicate treatment also up-regulated genes expression of long chain acyl Co A synthetase（LACS4）,β-ketoacyl Co A synthase（KCS10）,cytochrome P450 oxygenase（CYP86B1）,fatty acyl Co A reductase（FAR3）,glycerol-3-phosphate acyltransferase（GPAT1）and ATP-binding cassette transporter（ABCG6）,also increased activityes of LACS,KCS,CYP,FAR,and GPAT,and content of ABC transporter.5.Sodium silicate treatment enhanced activities of phenylalanine ammonia lyase （PAL）,cinnamate-4-hydroxylase（C4H）,and 4-coumarate coenzyme a ligase（4CL）at fruit wounds during healing.The contents ofρ-coumaric acid,caffeic acid,and sinapic acid were increased by sodium silicate treatment.Sodium silicate treatment enhanced activities ofρ-hydroxycinnamoyl-Co A:quinate shikimate（HCT）,ρ-coumarate 3-hydroxylase（C3H）,caffeoyl-Co A O-methyltransferase（CCo AOMT）,cinnamoyl-Co A reductase（CCR）,ferulate-5-hydroxylase（F5H）,and caffeic acid/5-hydroxyconiferaldehyde O-methyltransferase（COMT）at fruit wounds during healing,increased contents ofρ-coumaryl alcohol,coniferyl alcohol,sinapyl alcohol and lignin.Sodium silicate treatment increased peroxidase（POD）activity and hydrogen peroxide（H₂O₂）content,accelerated the deposition of SPP and lignin.In summary,sodium silicate treatment accelerated deposition of SPP,SPA,and lignin to form the wound healing tissues through activation of glucose metabolism,fatty acid metabolism,and phenylpropanoid metabolism at fruit wounds.Sodium silicate treatment promoted the accumulation of silicon.Wound healing tissues and silicon layersa as physical barriers can reduce weight loss and disease index,and enhance hardness.