Russeting in Apple is Initiated after Exposure to Moisture Ends: Molecular and Biochemical Evidence

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.

Russeting of Fruits: Etiology and Management

“…Second, experimental exposure of fruit surfaces to water, by immersion [73], by mounting a test tube filled with water on the fruit surface [38] or by overhead sprinkling [36], results in enhanced russeting. Indeed, these techniques are often used experimentally to induce russeting [37,158].…”

Identification of Novel Candidate Genes Involved in Apple Cuticle Integrity and Russeting-Associated Triterpene Synthesis Using Metabolomic, Proteomic, and Transcriptomic Data

“…Russeting detracts from fruit appearance, manifesting brownish rough corky texture on the fruit surface [ 1 ], leading to reduced market value and profitability on fruit production. Environmental stresses were one of the first characterized causes associated with russeting in apples [ 2 , 3 ]. Russeting seems to be initiated at the early stages of fruit development: the extreme mechanical tension on the fruit surface during this time of rapid growth seems to predispose apple fruit skin to cuticle microcracking [ 4 ].…”

Direct Evidence for a Radial Gradient in Age of the Apple Fruit Cuticle

“…Second, feeding 14 C labelled oleic acids to apple skin discs resulted in the incorporation of the label in hydroxy C18 acids such as 18-hydroxyoctadecenoic acid, 10,18-dihydroxyoctadecanoic acid, and 9,10,18-trihydroxyoctadecanoic acid (Kolattukudy et al, 1971 , 1973 ). These are major monomers of the apple fruit cutin (Walton and Kolattukudy, 1972 ; Straube et al, 2021 ). Also, until now the composition of apple cutin has been found to be consistent among all cultivars investigated (Holloway, 1973 ; Legay et al, 2017 ; Straube et al, 2021 ).…”

“…These are major monomers of the apple fruit cutin (Walton and Kolattukudy, 1972 ; Straube et al, 2021 ). Also, until now the composition of apple cutin has been found to be consistent among all cultivars investigated (Holloway, 1973 ; Legay et al, 2017 ; Straube et al, 2021 ). Third, the cutin of apple fruit has been classified as a “mixed-type cutin” comprising C16 and C18 monomers (Holloway, 1982 ).…”

“…The most likely explanation for the observed radial gradient in strain is a corresponding gradient in the deposition and thus the age of the cuticle. Additional factors that may contribute to a radial gradient in strain are the presence of polysaccharides on the inner side of the cuticle (Dominguez et al, 2011 ), a compositional gradient of C16/C18 cutin monomers within the cuticle with C18 fatty acids having a higher impact on cuticle integrity (Kolattukudy and Walton, 1972 ; Walton and Kolattukudy, 1972 ; Kolattukudy et al, 1974 ; Kolattukudy, 1980 ; Straube et al, 2021 ) and/or changing status of cutin polymerization (Espana et al, 2014 ; Martin and Rose, 2014 ).…”