Role of Ethylene in the Biosynthetic Pathway of Related-aroma Volatiles Derived from Fatty Acids in Oriental Sweet Melon

Abstract

<jats:p>The catabolism of fatty acid (FA) is regarded as a key pathway of aroma volatile compounds in oriental sweet melon (<jats:italic>Cucumis melo</jats:italic> var. <jats:italic>makuwa</jats:italic>). In our research, two cultivars of oriental sweet melon, Caihong7 and Tianbao, were employed to illuminate which step of the biosynthetic pathway of aroma compounds could be regulated by ethylene (ETH). The role of ETH in determining the profiles of straight-chain aroma volatile compounds, levels of FA as aroma precursors, activities of aroma-related enzymes derived from FA pathway, and expression patterns of key enzymes were investigated. Overall, exogenous application of ETH increased the production rates of endogenous ETH and levels of FA. Compared with control, the level of straight-chain esters, especially the acetate, hexanoate, and hexyl esters, was significantly increased by ETH, whereas the content of alcohol and aldehyde reduced. In addition, the metabolism of free FA included linoleic acid (LA), linolenic acid (LeA), and oleic acid (OA) appeared to be ETH-dependent. The activities of lipoxygenase (LOX), alcohol dehydrogenase (ADH), and alcohol acetyltransferase (AAT) as well as the expression patterns of <jats:italic>Cm-ADH1</jats:italic>, <jats:italic>Cm-ADH2</jats:italic>, <jats:italic>Cm-AAT1</jats:italic>, and <jats:italic>Cm-AAT4</jats:italic> were positively regulated by ETH. In contrast, hydroperoxide lyase (HPL) and <jats:italic>Cm-AAT2</jats:italic> and <jats:italic>Cm-AAT3</jats:italic> seemed to be independent of ETH modulation. These results suggested that the dissimilation of FA included LA, LeA, and OA into the acetate, hexanoate, and hexyl esters mainly through ETH regulating the LOX pathway by enhancing the expression of particular members of aroma-related key enzyme gene families as well as the activities of dehydrogenation and esterification.</jats:p>

HS-SPME-GC–MS Volatile Profile Characterization of Peach (Prunus persica L. Batsch) Varieties Grown in the Eastern Balkan Peninsula

“…Alcohol dehydrogenase in the fruit mesocarp accumulates throughout ripening [20], and alcohols are usually left undetectable by the consumers. Relatively low alcohol quantities suggest that the fruit is not overripe [42]. Fruit juice pH effectively converts alcohols and aldehydes into flavoring agents [42].…”

“…Relatively low alcohol quantities suggest that the fruit is not overripe [42]. Fruit juice pH effectively converts alcohols and aldehydes into flavoring agents [42].…”

Association among aroma volatiles and other traits in one near-isogenic line with firm flesh texture

“…The aroma profile and the textural traits discriminate climacteric from non-climacteric near-isogenic lines (NILs) at harvest or after postharvest (Obando-Ulloa et al, 2008 and, but little information is still available about aroma formation in non-climacteric melons particularly during postharvest ripening (Gonda et al, 2010) and in non-climacteric NILs during ripening. The emphasis in the flesh aroma of non-climacteric melons have focused in VOCs at harvest (Obando-Ulloa et al, 2010;Perry et al 2009;Verzera et al, 2011), and precursors such as branched amino acid and other amino acids (Gonda et al, 2010(Gonda et al, , 2013(Gonda et al, and 2018, fatty acids (Li et al, 2016). In other non-climacteric studies, most of the authors focused in differences between climacteric and non-climacteric types or among types or NILs (Bernillon et al, 2013 ;Güler et al, 2009;Obando-Ulloa et al, 2008), or among different rootstocks (Verzera et al, 2014), because VOC as a part of flavour is also of interest for fresh melon consumption (Escribano et al, 2010;Fernández-Trujillo et al, 2012a).…”

“…Various transcriptome studies allow the detection of the differences between melon cultivars (Saladie et al, 2015;Li et al, 2016;Zhang et al, 2016;Shin et al, 2017). New genetic and genomic tools are available for studying fruit ripening and generally the differentially expressed genes, including near-isogenic lines, tilling platforms, saturated genetic maps, the genome sequence, many QTLs and eQTLs positioned and gene expression atlas, etc.…”

“…C9 aliphatic aldehydes have been identified as the key aroma and flavour descriptors of commercial inodorus honeydew melons (Kyriacou et al, 2018). The emphasis on the flesh aroma of non-climacteric melons has focused on volatile organic compounds (VOCs) at harvest (Obando-Ulloa et al, 2010, Perry et al 2009Verzera et al, 2011), and precursors such as branched amino acids, other amino acids (Gonda et al, 2010(Gonda et al, , 2013(Gonda et al, and 2018, and fatty acids (Li et al, 2016). In other studies of non-climacteric fruit, most authors focused on differences between climacteric and non-climacteric types, among types or NILs (Bernillon et al, 2013;Güler et al, 2013;Obando-Ulloa et al, 2008), or among different rootstocks (Verzera et al, 2014), because VOCs, which contribute to flavour, are also of interest for fresh melon consumption (Escribano et al, 2010;Fernández-Trujillo et al, 2012).…”