Abstract
Exposure of the fruit surface to moisture during early development is causal in russeting of apple (Malus × domestica Borkh.). Moisture exposure results in formation of microcracks and decreased cuticle thickness. Periderm differentiation begins in the hypodermis, but only after discontinuation of moisture exposure. Expressions of selected genes involved in cutin, wax and suberin synthesis were quantified, as were the wax, cutin and suberin compositions. Experiments were conducted in two phases. In Phase I (31 days after full bloom) the fruit surface was exposed to moisture for 6 or 12 d. Phase II was after moisture exposure had been discontinued. Unexposed areas on the same fruit served as unexposed controls. During Phase I, cutin and wax synthesis genes were down-regulated only in the moisture-exposed patches. During Phase II, suberin synthesis genes were up-regulated only in the moisture-exposed patches. The expressions of cutin and wax genes in the moisture-exposed patches increased slightly during Phase II, but the levels of expression were much lower than in the control patches. Amounts and compositions of cutin, wax and suberin were consistent with the gene expressions. Thus, moisture-induced russet is a two-step process: moisture exposure reduces cutin and wax synthesis, moisture removal triggers suberin synthesis.
Highlights
Russeting is a surface disorder of many fruitcrop species including of apple [1,2,3,4,5]
Expressions of selected genes involved in cutin, wax and suberin synthesis were quantified, as were the wax, cutin and suberin compositions
During moisture exposure (Phase I) beginning at 31 days after full bloom (DAFB), genes involved in cutin (ABCG11, GPAT6) and wax (KCS10, SHN3, WSD1 and CER6) syntheses were significantly down-regulated compared to in the un-exposed control (Figures 1a–f and 2a–f)
Summary
Russeting is a surface disorder of many fruitcrop species including of apple [1,2,3,4,5]. Russeting is characterized by the formation of rough, brownish patches on the fruit skin. The impaired appearance of the skin reduces the fruit’s marketability and an associated increase in water vapor permeability compromises its postharvest performance [6]. Russet is the result of the formation of a periderm, the cell walls of the phellem being suberized. The periderm assumes the barrier functions of the epidermis and cuticle—the fractured epidermal cells soon drying and sloughing off. Despite of its economic importance, the sequence of processes that lead to russeting are not entirely clear
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