Role of Lipid Composition and Lipid Peroxidation in the Sensitivity of Fungal Plant Pathogens to Aluminum Chloride and Sodium Metabisulfite

Abstract

Aluminum chloride and sodium metabisulfite have shown high efficacy at low doses in controlling postharvest pathogens on potato tubers. Direct effects of these two salts included the loss of cell membrane integrity in exposed pathogens. In this work, four fungal potato pathogens were studied in order to elucidate the role of membrane lipids and lipid peroxidation in the relative sensitivity of microorganisms exposed to these salts. Inhibition of mycelial growth in these fungi varied considerably and revealed sensitivity groups within the tested fungi. Analysis of fatty acids in these fungi demonstrated that sensitivity was related to high intrinsic fatty acid unsaturation. When exposed to the antifungal salts, sensitive fungi demonstrated a loss of fatty acid unsaturation, which was accompanied by an elevation in malondialdehyde content (a biochemical marker of lipid peroxidation). Our data suggest that aluminum chloride and sodium metabisulfite could induce lipid peroxidation in sensitive fungi, which may promote the ensuing loss of integrity in the plasma membrane. This direct effect on fungal membranes may contribute, at least in part, to the observed antimicrobial effects of these two salts.Organic and inorganic salts are widely used in the food industry as preservatives and antimicrobials (26). These salts have a broad spectrum of antimicrobial activity with low mammalian toxicity (22), possess biocompatibility (13), and are generally recognized as safe. Several studies suggest that salts represent an interesting alternative to synthetic fungicides and could find application for the control of plant pathogens (13,20,22), particularly in the case of postharvest diseases that directly affect foodstuffs that will be consumed by the public (12, 21). Recently, organic and inorganic salts have revealed efficacy against postharvest pathogens affecting potato tubers (12,20,21,22,32). Of the tested salts, aluminum chloride and sodium metabisulfite were among the most efficient in controlling potato dry rot (Fusarium sambucinum [20]), soft rot (Erwinia carotovora [32]), and silver scurf (Helminthosporium solani [12]).Recent microscopic work with different potato pathogens, including the gram-negative bacterium E. carotovora (32) and the fungus F. sambucinum (T. J. Avis, M. Michaud, and R. J. Tweddell, unpublished data), has demonstrated that aluminum chloride and sodium metabisulfite produce changes in both bacterial and fungal cells, leading to loss of membrane integrity. Theses results are in agreement with other studies that have postulated that, under certain conditions, aluminum chloride and sodium metabisulfite may act through cell disruption, compromised membrane permeability, and lipid peroxidation (1,3,6,15,17,34).In an effort to gain better insight into the mode of action of these salts and in an attempt to ascertain biochemical determinants in the implicated mechanisms, four fungal potato pathogens were assayed with regard to (i) sensitivity toward aluminum chloride and sodium metabisulfite, (ii) intrinsic...

Antifungal activity of aluminium‐containing salts against the development of carrot cavity spot and potato dry rot

“…There have been numerous studies suggesting that these salts may represent an interesting alternative to synthetic fungicides. Recent literature also suggests that aluminium chloride is among the most efficient salts to control postharvest pathogens (Hervieux et al ., ; Mecteau et al ., , ; Mills et al ., , , ; Yaganza et al ., ; Avis et al ., ).…”

Sulphur dioxide evokes a large scale reprogramming of the grape berry transcriptome associated with oxidative signalling and biotic defence responses

“…No effective alternative to sulphur dioxide (SO 2 ) has been found for the table grape industry, despite much research and development. SO 2 and sulphites are effective against a broad spectrum of pathogens; they are thought to act directly on the pathogen through their strong nucleophilic properties, inactivating key regulatory proteins and altering membrane integrity (Avis, Michaud & Tweddell 2007). However, plants have developed numerous inducible mechanisms to cope with abiotic and biotic stress.…”

Antimicrobial activity of phosphites against different potato pathogens

“…Despite the similarities of our results with those mentioned above regarding relative sensitivity to Phi between oomycetes and fungi, to make extrapolations of the sensitivity of these pathogens to the entire kingdoms could be a mistake, because significant differences in the sensitivity to phosphorous acid related compounds were found within various classes of Oomycetes, and moreover, within a species (BASHAN et al 1990;WILKINSON et al 2001). On the other hand, AVIS et al (2007) reported that sensitivity to low doses of aluminum chloride and sodium metabisulfite, two chemicals capable of controlling post-harvest pathogens on potato tubers, showed similar behaviour in terms of relative sensitivity between oomycetes and fungi as in the present study with phosphites. In that report, they showed that EC 50 s of aluminum chloride and sodium metabisulfite for P. infestans, R. solani and F. sambucinum also differed in at least one order of magnitude, being the oomycete the most sensitive of these pathogens analysed.…”