Submitted to: Journal of Horticultural Science and Biotechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/15/2005
Publication Date: 11/1/2005
Citation: Curry, E.A. 2005. Ultrastructure of epicuticular wax aggregates during fruit development of apple (malus domestica borkh.). Journal of Horticultural Science and Biotechnology. 80:668-676. Interpretive Summary: WHY: In apples, external skin disorders are often linked to weather conditions at a specific developmental stage during the growing season and include frost ring, russet, stain, sunburn, cracking, splitting, flecking, lenticel marking, sunscald and superficial storage scald. This initial study investigated the nature of apple wax growth to improve understanding of cuticle growth and development, and conditions that may alter its composition, structure and function. WHAT: To determine how the apple peel develops, structure of wax platelets on the surface of 'Delicious' apple fruit was investigated throughout the growing season using field emission scanning electron microscopy. Samples were taken at flowering and every 2 weeks thereafter until harvest. RESULT: The ultrastructure of apple fruit surface wax platelets changed little from early growth to harvest. The cuticle is a dynamic organ which grows along with the apple by a combination of stretching, sharing and healing of the scars, all without exposing the sensitive cells beneath. A model of this process was proposed. This information is important to determine how certain surface disorders develop.
Technical Abstract: Development of wax platelets on the surface of 'Delicious' (Malus domestica Borkh.) apple fruit was investigated throughout the growing season using field emission scanning electron microscopy. At 5,000 x and greater, wax crystalline structures appeared to be composed of microtubules (MT), aggregates of individual MT to form single platelets and of one or more platelets. Thickness of a single wax platelet ranged from 116-128 nm, approximately the diameter of a single MT, whereas multiple-platelet aggregates ranged in visible throughout fruit development as well as on different apple cultivars. Examination of cuticle from young fruitlets (receptacle diameter + 3 mm) of 'Chinese Crabapple' (Malus hupehensis Rehd.), which develops without trichomes, best demonstrated early platelet formation. A model of wax platelet and cuticle development on apples is proposed based on these data.