The domestic apple might well be called an 'extreme' fruit. In the arid Northwest United States, the fruit often tolerates
surface temperatures ranging from -2 °C in the early spring to 50 °C in the heat of summer, and again to -2 °C during
controlled postharvest storage for up to 12 months. During its 18-month existence, the apple maintains a cuticle that is
dynamic and environmentally responsive to protect against 1) cellular water loss during desiccation stress and 2)
excessive uptake of standing surface moisture. Physiological disorders of the peel such as russeting, cracking, splitting,
flecking and lenticel marking, develop as epidermal cells respond to rapid changes in ambient conditions at specific
developmental stages during the growing season. Resultant market losses underlie research investigating the nature of
apple cuticle growth and development. Ultrastructural analysis of the pro-cuticle using scanning electron microscopy
indicates an overlapping network of lipid-based distally-elongating microtubules--produced by and connected to
epidermal cells--which co-polymerize to form an organic solvent-insoluble semi-permeable cutin matrix. Microtubule
elongation, aggregation, and polymerization function together as long as the fruit continues to enlarge. The nature of
lipid transport from the epidermal cells through the cell wall to become part of the cuticular matrix was explored using
an FEI Helios NanoLabTM DualBeamTM focused ion beam/scanning electron microscope on chemically- and cryo-fixed
peel tissue from mature or freshly harvested apples. Based on microtubule dimensions, regular projections found at the
cell/cuticle interface suggest an array of microtubule-like structures associated with the epidermal cell.
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