Chemical composition and morphology of apple cuticular wax during fruit growth and development

Cuticular wax covers the surface of the apple epidermis and plays an important role in water loss and pathogen resistance. However, little is known about wax biosynthesis during apple fruit development. In this study, the morphological structure and chemical composition of wax and the transcription patterns of wax-related genes were investigated in the 'Red Delicious' and 'Golden Delicious' cultivars. The results showed that accumulation of the waxy layer was synchronized with enlargement and maturation of fruit. The crystal structure, major chemical components (very long chain fatty acids and triterpenes) of wax and the expression levels of wax-related genes varied significantly 90 days after flowering (DAF), indicating that the critical period for biosynthesis of cuticular wax was about 90 DAF. This finding is valuable for further study of the regulatory mechanism of wax biosynthesis at both the molecular and physiological levels.