Disappearance of the Cuticle and Wax in Outermost Layer of Callus Cultures and Decrease of Protective Ability against Microorganisms

In electron microscopic observation, neither wax nor cuticle was observed on the outermost layers of callus tissues. Chemical estimation of wax in the callus surface was attempted by thin-layer chromatography of solvent extracts of callus tissues in comparison with those of barley and rice leaves. Hydrocarbons and free alcohols were detected in lyophilized callus tissues, but no wax esters or ketones were detected. Germination test indicated that germination of spores of Aspergillus oryzae was less favored on hydrophobic membranes than that of spores of Alternaria sp. and Botrytis cinerea.

From these results, we inferred that the lack of cuticle and wax in the outermost layer of callus tissues facilitated spore germination and penetration, and A. oryzae, a saprophytic fungus, could also readily penetrate into callus tissues.