Abstract
The peptide PAF56 (GHRKKWFW) was reported to be an effective control for the main diseases of citrus fruit during postharvest storage. However, the mechanism of action of PAF56 is still unknown. In this paper, PAF56 might not induce defense resistance of citrus fruit. The SEM results visually indicated that the fungi mycelia became shrunken and distorted after being treated with PAF56. The destructive effects of PAF56 on the mycelial cell membrane of three kinds of pathogenic fungi (Penicillium digitatum, Penicillium italicum, and Geotrichum citri-aurantii) were verified by the K+ leakage and the release of nucleic acid. Furthermore, the interaction between peptide PAF56 and the pathogen spores was investigated, including the changes in cell membrane permeability and dynamic observation of the interaction of fluorescein labeled TMR-PAF56 and Geotrichum candidum spores. The results indicated that the antifungal activity of PAF56 on spores was time-dependent and directly related to the membrane damage. This research provided useful references for further research and practical application of peptides.
Highlights
Citrus is the type of fruit crop with the highest production worldwide, and the citrus industry has great economic importance
We studied the effect of PAF56 on spores, and the mechanism related to cell membrane was further explored focusing on two aspects of fungal spores and mycelia
The disease incidence and lesion diameter results show there were no significant difference between the citrus fruit inoculated with PAF56 tthheerecwoenrteronol gsirgonuifipcainntodciufflearetendcewbeittwhesetnetrhileecidtriusstiflrluedit iwnoactuelratdeduwriinthg PtAhFe5w6 ahnodlethpe eriod o cdoinsteroalsgeroduepveinloocpumlateendt.wTithhestererisleudltisstiflolerdtwheatethr dreuerinkginthdeswohfopleaptheroiogdenoifcthfeudnigsei,asPe. italicu darddeneisugdviscieGttelaao.ntdpcucameemnfeeod,nifndatcsu.nietmTdrhru,eewsGsrfe.iresruscetuaiatsnl.nitmdsciefidolauorrmft,hwc,eihtwtrihcuerhsereedfreksumiinmiotd.nislsaotrrfa,ptweasthhtohicgahet nPdiAceFfmu56nogmni,sigPtrh. aitttaneloisctutimhnda, tuP.cPdeAidgiFetfa5et6numsme, ight no
Summary
Citrus is the type of fruit crop with the highest production worldwide, and the citrus industry has great economic importance. Penicillium digitatum (green mold), P. italicum (blue mold), and Geotrichum citri-aurantii (sour rot) are well known as the predominant citrus pathogens causing postharvest diseases during fruit storing and transportation. Increasing antimicrobial peptides has been proved to be able to control infectious diseases of fruit and vegetables such as citrus and tomato [1,2,3]. PAF56 exhibited an effective control on green and blue mold and sour rot in citrus fruit without a hemolytic effect. The fungicidal mechanism of the control of PAF56 for the diseases of citrus fruit has not been revealed. It is not clear whether the mechanism of the control of active peptide PAF56 for those diseases is related to induced fruit defense resistance. Fungi initiate their infection by disseminating spores, and spores swell and germinate into hyphae, which results in severe yield loss in the citrus industry
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