Biosynthesis of phenolic compounds and its regulation in apple

Of particular interest are the proanthocyanidins, or condensed tannins, polymeric flavonoids which are induced by stress and have many interesting ecological activities. We have shown how a single gene (a MYB transcription factor) controls the entire proanthocyanidin pathway, and we are now studying other regulatory genes and proteins hypothesized to act in concert with this MYB. We are also investigating biosynthetic genes such as flavonoid glycosyl transferases and acyl transferases, which are hypothesized to contribute to poplar defense and phenolic synthesis. Understanding the synthesis of the proanthocyanidin has broad implications, since these chemicals are found in food plants (such as apples and blueberries) and are important in the maintenance of human health.

Biosynthesis of phenolic compounds and its regulation ..

Biosynthesis of phenolic compounds and its regulation in ..

Biosynthesis of phenolic compounds and its regulation in apple.

To understand the role of ethylene in regulating the overall flavor of apple fruits, ethylene production or action was reduced using transgenic apple trees suppressed for ACC-synthase or ACC-oxidase enzyme activity or by the addition of 1-methylcyclopropene (1-MCP), an ethylene action inhibitor. Flavor components were differentially regulated in response to the suppression of both ethylene biosynthesis and action. Headspace analysis of aroma production, an ethylene-associated event, showed a reduction in ester and alcohol production in the ethylene-suppressed lines and in the apples treated with 1 μL L-1 1-MCP for 20 h at 20 °C. However, no major differences were observed in the concentrations of aldehyde volatiles. Other flavor metabolites that showed an ethylene-dependent pattern were organic acids and sugars. Malic acid degradation was significantly reduced under ethylene-suppressed conditions, showing a recovery after the fruit was exposed to ethylene. Sucrose and fructose concentrations were influenced by suppression or enhancement of ethylene. Total phenolics as well as individual phenolic compounds showed an ethylene-dependent regulation only in response to the suppression of ethylene biosynthesis, but not when ethylene action was inhibited.

of phenolic compounds and its regulation in apple.

Moreover, fruit bagging can reduce levels of the light-absorptive compound – anthocyanin ( Li et al., 2008 ), resulting in a higher sensitivity of bagged fruit to sunlight irradiation, which improves fruit appearance by promoting anthocyanin synthesis when bagged fruits are re-exposed to sunlight ( Arakawa, 1988; Ju, 1998; Wang et al., 2000; Bakhshi and Arakawa, 2006 ).Apple peel is a major source of phenolic compounds, especially flavonols and anthocyanins ( Treutter, 2001; Bakhshi and Arakawa, 2006; Renard et al., 2007; Chen et al., 2012 ).

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