Chemical Composition of Cuticle and Barrier Properties to Transpiration in the Fruit of (Lour.) Skeels.

The plant cuticle, as a lipid membrane covering aerial plant surfaces, functions primarily against uncontrolled water loss. Herein, the cuticle chemical composition and the transpiration of wampee fruit ( (Lour.) Skeels) at the green, turning, and yellow stages in cultivars of "Jixin" and "Tianhuangpi" were comprehensively studied. The coverage of wax and cutin monomers per unit of fruit surface area at the green stage was lower in "Jixin" than in "Tianhuangpi" and increased gradually during development. Cutin monomers accumulated ranging from 22.5 μg cm (green) to 52.5 μg cm (turning) in "Jixin" and from 36.5 μg cm (green) to 81.7 μg cm (yellow) in "Tianhuangpi." The total composition of waxes ranged between 6.0 μg cm (green) and 11.1 μg cm (turning) in "Jixin," while they increased from 7.4 μg cm (green) to 16.7 μg cm (yellow) in "Tianhuangpi." Cutin monomers were dominated by ω-, mid-dihydroxy fatty acids (over 40%), followed by multiple monomers of α,ω-dicarboxylic acids with or without added groups, α-monocarboxylic acids with or without ω- or mid-chain hydroxy or mid-epoxy groups, primary alcohols, and phenolics. The very-long-chain (VLC) aliphatic pattern of cuticular waxes was prominently composed of -alkanes (ranging from 21.4% to 39.3% of total wax content), fatty acids, primary alcohols, and aldehydes. The cyclic waxes were dominated by triterpenoids (between 23.9 and 51.2%), sterols, and phenolics. Water loss in wampee fruit exhibited linear changes over time, indicating an overall monofunctional barrier to transpiration. Permeance for water in wampee fruit was higher at the green stage than at the yellow stage in both "Jixin" and "Tianhuangpi," which showed a negative correlation with the changes of VLC -alkanes. The results showed the cuticular chemicals, including cutin monomers and waxes, in wampee fruit and further indicated the potential contributions of the cuticular chemical composition to the physiological functions in fruits.