Target metabolite and gene transcription profiling during the development of superficial scald in apple (Malus x domestica Borkh)

Abstract

BackgroundFruit quality features resulting from ripening processes need to be preserved throughout storage for economical reasons. However, during this period several physiological disorders can occur, of which superficial scald is one of the most important, due to the development of large brown areas on the fruit skin surface.ResultsThis study examined the variation in polyphenolic content with the progress of superficial scald in apple, also with respect to 1-MCP, an ethylene competitor interacting with the hormone receptors and known to interfere with this etiology. The change in the accumulation of these metabolites was further correlated with the gene set involved in this pathway, together with two specific VOCs (Volatile Organic Compounds), α-farnesene and its oxidative form, 6-methyl-5-hepten-2-one. Metabolite profiling and qRT-PCR assay showed these volatiles are more heavily involved in the signalling system, while the browning coloration would seem to be due more to a specific accumulation of chlorogenic acid (as a consequence of the activation of MdPAL and MdC3H), and its further oxidation carried out by a polyphenol oxidase gene (MdPPO). In this physiological scenario, new evidence regarding the involvement of an anti-apoptotic regulatory mechanism for the compartmentation of this phenomenon in the skin alone was also hypothesized, as suggested by the expression profile of the MdDAD1, MdDND1 and MdLSD1 genes.ConclusionsThe results presented in this work represent a step forward in understanding the physiological mechanisms of superficial scald in apple, shedding light on the regulation of the specific physiological cascade.

Apple fruit superficial scald resistance mediated by ethylene inhibition is associated with diverse metabolic processes

“…Among the phenolic compounds accumulating during scald development, the most abundant is chlorogenic acid. As a consequence of the loss of membrane integrity, chlorogenic acid, which is stored in the vacuole, reacts with PPO enzyme originating in the chloroplast, leading to the discoloration that is typical of superficial scald (Golding et al ., ; Busatto et al ., ).…”

“…The expression profiles were further validated by analyzing the transcriptional pattern of 10 selected candidate genes (Table S11) as in Busatto et al . ().…”

“…The concentration of α‐farnesene increases throughout ripening in parallel with ethylene, and it accumulates mainly in the epicuticular wax layer, while the dark coloration that is diagnostic of superficial scald mainly occurs in the hypodermal and epidermal cells (Bain, ; Bain and Mercer, ; Barden and Bramlage, ). The metabolism of phenolic compounds has been proposed as an alternative cause of superficial scald and, while the antioxidant properties of phenols can help prevent scald development, their ethylene‐regulated oxidation, catalyzed by polyphenol oxidase (PPO), can result in brown coloration (Busatto et al ., ). The tissue discoloration is most probably caused by the interaction between PPO, which accumulates in the chloroplast, and chlorogenic acid, which is stored in the vacuole, following a loss of membrane integrity.…”

An insight into the role of fruit maturity at harvest on superficial scald development in ‘Beurré D’Anjou’ pear

“…It is hence likely, that as specified in apples , specific antioxidants rather than the fruit antioxidant potential itself are key elements in determining the fruit susceptibility to superficial scald. For instance, Busatto et al (2014) recently showed that, in apples, the actual manifestation of superficial scald symptoms resulted from an accumulation of chlorogenic acid and its further oxidation carried out by a polyphenol oxidase (PPO). Whether greater or lower amounts of antioxidants in the fruit are beneficial to prevent the appearance of superficial scald in 'Beurrè d'Anjou' pears, needs to be further confirmed.…”

Pre-harvest climate and post-harvest acclimation to cold prevent from superficial scald development in Granny Smith apples

“…The symptomatic peel browning would result from 1 IRHS-UMR1345, Université d'Angers, INRAE, Institut Agro, SFR 4207 QuaSaV, 49071, Beaucouzé, France. 2 open the enzymatic oxidation of the accumulated chlorogenic acid by the polyphenol oxidase (PPO), both initially in separate compartments 8 .…”