Studies On The Mechanisms Of DNP And ATP Regulating The Disease Development Of Harvested Longan Fruit Infected By Phomopsis Longanae Chi

Longan(Dimocarpus longan Lour.)is a kind of subtropical fruit with high nutrient and commercial values,however the high temperature and humidity at its harvested season easily causes the latent pathogen to infect the fruits with a result of pericarp browning and fruit deterioration.These greatly limited the long distance transpotation and sales of longan fruits.Our previous found that energy deficiency could promote the pericarp browning of harvested longan fruit,while the Phomopsis longanae Chi(P.longanae)is the primary latent pathogen which caused the longan pericapr browning and deterioration,moreover the energy charge and adenosine triphosphate(ATP)of longan fruit would be greatly reduced after infected by P.longanae.Therefore we conclude that fruit disease might related to energy deficiency.However it is still unclear that the specify mechanism of longans' harvested diseases,and also the effects of energy on the diseasing and its relationship with harvested physiological metabolisms.Thus,basing on the previous researches,this study focus on the effects of 2,4-dinitrophenol(DNP)and ATP on longan disease caused by P.longanae and their relationship between different metabolisms of energy,respiration,reactive oxygen,antifungal substance and cell wall.Also,the effects of ATP treatment on postharvest physiology,quality and storage behavior of longan fruit would be investigated.The aims of this work is to find out the real mechanism of longan fruit disease and provide the scientific theory and alternative methods for disease control.The results as followed:1.DNP treatment promoted the disease index and browning index in P.longanae-infected longan fruit,accelerated the diseasing progress;ATP treatment decreased the disease index and browning index in P.longanae-inoculated fruits,inhibited the disease.2.DNP treatment decrease the ATP level and energy charge of P.longanae-inoculated longan fruits,inhibited the Ca2+-ATPase and H+-ATPase in protoplasm,vacuole and mitochondria,damaged the balance between Ca2+and H+,and finally changed the osmotic pressure of membrane and membrane structure.ATP treatment could maintain the higher level of ATP and energy charge,inhibited the activities of ATPase in protoplasm,vacuole and mitochondria,and protected the membrane structure.3.DNP treatment increased the respiration rate and the activities of cytochrome C oxidase(COX),ascorbic acid oxidase(AAO)and polyphenol oxidase(PPO)(terminal oxidase)in the pericarp of P.longanae-inoculated fruits,restrained the activities of nicotinamide adenine dinucleotide kinase(NADK),enhanced the content of oxidized form of nicotinamide adenine dinucleotide(NAD)and reduced form of nicotinamide adenine dinucleotid(NADH),reduced the content of oxidized form of nicotinamide adenine dinucleotide phosphate(NADP)and reduced form of nicotinamide adenine dinucleotide phosphate(NADPH),and finally weakened pentose phosphate pathway.ATP treatment significantly decreased the respiration rate and the activities of terminal oxidase in the pericarp of P.longanae-inoculated fruits,decreased the content of NAD and NADH,and increased the NADP and NADPH content,enhanced pentose phosphate pathway.4.DNP treatment enhanced the O2-production rate of P.longanae-inoculated fruits,accelerated the products malondialdehyde(MDA)of membrane peroxide reaction,decreased the activities of superoxide dismutase(SOD),catalase(CAT)and ascorbate peroxidase(APX)(reactive oxygen scavenging enzymes),promoted the reduced ascorbic acid(AsA)and reduced glutathione(GSH)(reactive oxygen scavenging substance),and then decreased the 1,1-diphenyl-2-picrylhydrazyl(DPPH)scavenging ability and reduction ability,finally leaded to over-accumulation of reactive oxygen species(ROS)and the increasing reaction of membrane peroxide.ATP treatment obviously decreased the O2-production rate of P.longanae-inoculated fruits,inhibited the production of MDA,and increased the activities of reactive oxygen scavenging enzymes and substance,enhanced the DPPH scavenging ability and reduction ability,and then maintained the balance between ROS production and scavenging,alleviated the membrane peroxide.5.DNP treatment enhanced the activities of lipoxygenase(LOX),lipase and phospholipase D(PLD)(enzymes related to fatty acid degradation)in the pericarp of P.longanae-inoculated fruits,accelerated the degradation of linoleic acid(C18:2),linolenic acid(C18:3)and gondoic acid(C2O:1),enhanced the relative content of palmitic aicd(C16:0)and stearic acid(C18:0),consequently decreased the ratio of unfatty acid to fatty acid(U/S)with an increase of membrane permeability,finally damage the membrane structure;ATP treatment significantly decreased the activities of enzymes related to fatty acid degradation in the pericarp of inoculated fruits,alleviated the degradation of unfatty acid and the increase of fatty acid,maintained higher index of unfatty acid(IUFA),inhibited the change of fatty acid components,and finally protected the membrane integrity.6.DNP treatment significantly decreased the activities of phenylalanine ammonia-lyase(PAL),PPO and POD in pericarp of P.longanae-inoculated fruits in the earlier storage period,and then inhibited the synthesis of lignin and quinine(the production of oxide reaction between phenolics and PPO,peroxidase(POD)which could poison the pathogen;during the later storage period,DNP treatment promoted the activities of PPO and POD with a result of phenolic rapid oxidation and pericarp browning.Moreover,DNP treatment kept a relative lower activities of PAL,chitinase(CHI)and ?-1,3-glucanase(GLU)(pathogen resistance-relative enzymes),decreased the disease resistance of inoculated longan fruit.Higher activites of PAL,PPO and POD and higher content of lignin and phenolics in the earlier storage time were showed in the inoculated fruits with ATP treatment;During the later storage,ATP lowered PPO and POD activities,inhibited the phenolics oxidation followed by lower browing index;ATP treatment could also maintain higher CHI and GLU activities,consequently enhance the disease resistance.7.DNP treatment significantly promoted the activities of polyethylene(PE),polygalacturonase(PG),cellulase(Cx)and ?-galactosidase in pericarp of P.longanae-inoculated fruits,improved the degradation of cell wall materials and the degradation of covalent-bound pectin to ionic-bound pectin and to water-soluble pectin,decreased the content of cellulose and hemicellulose,consequently damaged the cell wall structure;ATP treatment decreased the activities of PE,PG,Cx and ?-galactosidase in pericarp of P.longanae-inoculated fruits,inhibited the degradation of pectin,cellulose and hemicelluloses,and protected the cell wall structure.8.The application of ATP could significantly reduce fruit respiration rate,delay an increase of cell membrane permeability in pericarp,maintained higher contents of chlorophyll,carotenoid,anthocyanin and flavonoid in pericarp and subsequently retard the change of apparent color of longans,in addition,significantly decrease PPO activity and reduce the decrease of total phenolics content in pericarp and subsequently reduce browning index in longan pericarp.The application of ATP also could effectively inhibit the decreases of contents of total soluble solids(TSS),total soluble sugars and vitamin C,and retard an increase of titratable acid(TA)content in pulp,and subsequently maintain better quality and flavor in longan pulp.Furthermore,ATP treatment could maintain higher rate of healthy fruit,and effectively reduce weight loss from longans,with the developments of aril breakdown and fruit disease in longan fruit retarded.It could be concluded that 0.8 mM ATP treatment could effectively delay fruit senescence,maintain higher fruit quality,and exhibit better storage behavior of longan fruit.Thus,it is suggested that application of ATP may be a promising method for maintaining quality and extending shelf life of harvested 'Fuyan' longan fruit.