Ethylene enhances the antifungal lipid content in idioblasts from avocado mesocarp

It has previously been demonstrated that exposure of whole avocado fruits cv. Fuerte to 40 μl/l ethylene for 3 hours enhances the level of antifungal 1-acetoxy-2-hydroxy-4-oxo-heneicosa-12, 15-diene (diene) in the fruit pericarp. Exposure of 1-2 mm slices of fruit pericarp and mesocarp to ethylene enhanced the level of the antifungal diene in the mesocarp only. Since most of the antifungal diene in the mesocarp is compartmentalized in idioblasts, the effect of ethylene was tested on isolated idioblasts. Exposure of idioblasts to ethylene increased the level of antifungal diene twofold within 3 hours. This effect was temperature dependent. Three hours exposure of idioblasts to ethylene at 35°C doubled the diene content compared to less than 50% increase after three hours at 20°. Incubation of idioblasts with [2-¹⁴C]malonyl-CoA or [1-¹⁴C]acetate in the presence of ethylene, showed the incorporation of the label into a compound that co- chromatographed with the antifungal diene. The compound induced by ethylene and released from the cells was identified by NMR as the antifungal diene. The present report suggests that ethylene can induce the synthesis of the antifungal diene in idioblasts and the export of this compound to the pericarp of the fruits.