Mechanism Of Induced Resistance Of Fruit In Response To Sodium Silicate

Disease caused by fungal infection is a critical factor which is responsible forpostharvest loss and decay of fresh fruits and vegetables. Currently, chemicalfungicides treatment is primary and effective method for controlling these diseases.However, due to problems related to fungicide residues, environmental pollutions andfungicide resistance by pathogens, there is a worldwide trend to reduce or restrict touse of chemical fungicides. Induce resistance, as one kind of new and safe strategy forcontrolling postharvest disease, have a potential ability to instead or reduceapplication of chemical fungicides. Furthermore, previous studies have shown thattreatment with soluble silicate could reduce postharvest disease of some fruits throughinducing resistance. In the present study, fruits of ‘Zaosu’ pear,‘Fuji’ apple and‘Yujinxiang’ muskmelon were chosen as materials, and multiple approaches involvingthe postharvest pathology, biochemistry and proteomics have been used to investigatecontrol effective of sodium silicate treatment on major postharvest disease in the threekinds of fruits above mentioned, to study the effect of treatment on metabolism oraccumulation of hydrogen peroxide in fruits, and to analyze effect of treatment onproteomic changes in muskmelon fruit. Main results were following:1.100mM sodium silicate treatment can significantly inhibit blue mold caused byPenicillium expansum in ‘Zaosu’ pear fruit during storage. Moreover, enhancement ofperoxidase (POD) activity and reduction of activities of catalase (CAT) and ascorbateperoxidase (APX) were found in Si-treated fruit.0.1mmol/L sodium silicate treatmentby using inoculation method can also significantly control blue mold of ‘Zaosu’ pearfruit. However, Si treatment combined with DPI reduced the ability of controllingblue mold in fruit, which were consisted with inhibition of hydrogen peroxide (H2O2)content and NADPH oxidase (NOX) activity in integration treated fruit.2.200mM sodium silicate treatment resulted in alleviation of incidence of disease,and inhibition of development of lesion of apple fruit inoculated with P. expansum.Compared with the control, both superoxide dismutase (SOD) and NOX activities inthe treated fruit were significantly higher after treatment, while CAT and APXactivities were significantly lower，which were associated with the significant increaseof superoxide (02-) production and H202content after treatment respectively. Furthermore, the inhibition of the activity of NOX by DPI also resulted in inhibitionof H2O2content, and accelerating development of lesion.3. The timing of accumulation of H2O2and response to resistance againstTrichothecium roseum in melon fruit treated with100mM sodium silicate byimmersion method were investigated in this study. The results of dying by DABsuggested that the initiation of H2O2accumulation was4hours after treatment. From12to48hours after treatment, Si-treated fruit had ability to inhibiting pink rot.Meanwhile, the results of Si treatment combined with DPT indicated thataccumulation of H2O2in fruits at the time after24hours treatment were correlatedwith the ability to resistance against pink rot.4. To obtain unique insights regarding the effect of induced resistance onpostharvest Si treatments in muskmelons (cv. Yujinxiang) challenged with T. roseum,a complete proteome analysis was performed by using two dimensional gelselectrophoresis (2-DE) followed by matrix-assisted laser desorption ionization time offlight mass spectrometry (MALDI-TOF-MS). A total of81proteins were identified assignificantly up-or down-regulated in response to Si induction and T. roseuminoculation in fruits. After functional categorization, these proteins were attributed toenergy pathway, metabolism, redox homeostasis, disease/defense response, secondarymetabolism, protein metabolism, transporter and cell structure etc. Among them, both8defense response proteins including peroxidase, peroxidase precursor, heat shockprotein70, hsp90-2-like, desiccation-related protein, stress-induced protein sti1-likeprotein,26kDa phloem lectin and17kDa phloem lectin were correlated with defenceresponse, which were involved resistance directly or inderectly. Futhermore,5redoxhomeostasis associated proteins containing ascorbate oxidase, catalase,monodehydroascorbate reductase, glutathione transferase, glutathione s-transferasewere belongs to antiodixant proteins, which were involved to metabolism of reactiveoxygen species. In addition, more than10proteins identified as the enzymesassociated with energy metabolism were also involved in induced resistance ofmuskmelon fruits by Si and challenged by T. roseum.5. The effect of postharvest Si treatments on changes of proteome in muskmelonfruit at36hours after treatment were also investigated by iTRAQ technique. A total of 94polypeptides whose abundance changed in response to the elicitor were identified36hours after the treatments. These altered proteins attribute to energy pathway,protein synthesis, defence response, metabolism, signal transduction, transcription andothers. Among them, many proteins associtated with defence response such ashypersensitive-induced response protein, netting associated peroxidase, peroxidase，endochitinase MCHT-2, thermoinhibition-associated THB-4protein, pollen coatprotein, classical AGP and wound-induced protein were identified as up-regulatedproteins, which can involve in resistance response in fruits.In conclusion, the results of the present study indicated that sodium silicate hasan ability of inducing disease resistance in three fruits including pear, apple andmuskmelon. Meanwhile, the induced resistance of fruits in response to sodium silicateclearly correlated with the accumulation of hydrogen peroxide, enhancement ofactivities of enzymes related defense response, and regulation of proteomics in fruits.Furthermore, these results have an important significance of theoretical guidance forexploring the mechanisms of induced resistance of fruits in response to sodiumsilicate in the future. Moreover, this suggested sodium silicate could be a promisingstrategy in reducing postharvest disease and partially substituting chemical fungicidesto control postharvest disease in fruits and vegetables.