Cinnamaldehyde Exerts Its Antifungal Activity by Disrupting the Cell Wall Integrity of Geotrichum citri-aurantii.

Qiuli Ouyang,Lu Li,Nengguo Tao,Xiaofang Duan

doi:10.3389/fmicb.2019.00055

Abstract

Our previous study showed that cinnamaldehyde (CA) significantly inhibited the mycelial growth of Geotrichum citri-aurantii, one of the main postharvest pathogens in citrus fruits. This study investigated the antifungal mechanism of CA against G. citri-aurantii. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images showed that CA treatment led to clear morphological changes in the cell walls and membranes of G. citri-aurantii. However, the membrane integrity, total lipids and ergosterol contents were not apparently affected by CA treatment. Notably, the extracellular alkaline phosphatase (AKP) activity was increased after CA treatment, suggesting impairment in cell wall permeability. A weakened fluorescence in the cell wall, a decrease in the chitin contents, and changes of ten genes involved in cell wall integrity were also observed. These results suggested that CA may exhibit its antifungal activity against G. citri-aurantii by interfering the build of cell wall and therefore lead to the damage of cell wall permeability and integrity.

Highlights

Worldwide citrus sour rot caused by Geotrichum citri-aurantii, which is less common than green and blue molds, has been reported as an important postharvest disease of citrus fruits, during periods of high rainfall (McKay et al, 2012; Zhou et al, 2014)
Our previous study showed that CA significantly inhibited the mycelial growth of G. citri-aurantii with a minimum inhibitory concentration (MIC) and minimum fungicidal concentration (MFC) of Antifungal Mode of Cinnamaldehyde Against G. citri-aurantii
The objective of this research was to reveal the antifungal mechanism of CA against G. citri-aurantii by determining the following: (i) the morphology and ultrastructure of cell membranes using Scanning electron microscopy (SEM) and transmission electron microscopy (TEM), (ii) the plasma membrane integrity and the total lipid and ergosterol contents, (iii) the extracellular alkaline phosphatase (AKP) activity, the calcofluor white stain results and chitin contents, (iv) and the expression levels of genes involved in cell walls

Summary

Introduction

Worldwide citrus sour rot caused by Geotrichum citri-aurantii, which is less common than green and blue molds, has been reported as an important postharvest disease of citrus fruits, during periods of high rainfall (McKay et al, 2012; Zhou et al, 2014). The concentration of SOPP required to effectively manage sour rot can result in the development of oleocellosis and darkening of the fruit rind (Regnier et al, 2014; Zhou et al, 2014). Many studies highlight the feasibility of applying essential oils for postharvest disease control in citrus due to their notable antifungal activity against G. citri-aurantii and substantially lower risk for the development of resistance (Talibi et al, 2012; Regnier et al, 2014; Wuryatmo et al, 2014). Our previous study showed that CA significantly inhibited the mycelial growth of G. citri-aurantii with a minimum inhibitory concentration (MIC) and minimum fungicidal concentration (MFC) of Antifungal Mode of Cinnamaldehyde Against G. citri-aurantii

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Conclusion