Abstract
BackgroundBlack carrots (Daucus carota ssp. sativus var. atrorubens Alef.) constitute a valuable source of anthocyanins, which are used as natural red, blue and purple food colourants. Anthocyanins and phenolic compounds are specialised metabolites, accumulation of which often requires elicitors, which act as molecular signals in plant stress responses. In the present study, ethephon, an ethylene-generating compound was explored as enhancer of anthocyanin and phenolic contents during growth of ‘Deep Purple’ black carrots. The effects of ethephon on several parameters were investigated, and the expression of biosynthetic anthocyanin genes was studied during growth and anthocyanin accumulation.ResultsRoots of ethephon-treated carrot plants exhibited an increase in anthocyanin content of approximately 25%, with values ranging from 2.25 to 3.10 mg g−1 fresh weight, compared with values ranging from 1.50 to 1.90 mg g−1 fresh weight in untreated roots. The most rapid accumulation rate for anthocyanins, phenolic compounds, soluble solids and dry matter was observed between 10 and 13 weeks after sowing in both untreated and ethephon-treated carrots. The differences in anthocyanin contents between untreated and treated carrots increased for several weeks after the ethephon treatment was terminated. Five cyanidin-based anthocyanin forms were identified, with variable relative abundance values detected during root growth. Overall, the expression of the anthocyanin biosynthetic genes analysed (PAL1, PAL3, F3H1, DFR1, LDOX2) increased in response to ethephon treatment, as did the expression of the MYB1 transcription factor, which is associated with activation of the phenylpropanoid pathway under stress conditions. In addition, a correlation was proposed between ethylene and sugar contents and the induction of anthocyanin synthesis.ConclusionsThis study presents a novel method for enhancing anthocyanin content in black carrots. This finding is of economic importance as increased pigment concentration per unit of biomass implies improved profitability parameters in food colour production. We provide new insight into the accumulation patterns of the different cyanidin-based anthocyanins and phenolic compounds during root growth. Moreover, we show that enhanced anthocyanin content in ethephon-treated carrots is accompanied by increased expression of anthocyanin biosynthetic genes.
Highlights
Black carrots (Daucus carota ssp. sativus var. atrorubens Alef.) constitute a valuable source of anthocyanins, which are used as natural red, blue and purple food colourants
In mature black carrot taproots, acylated cyanidin glycosides represent the major fraction of anthocyanin compounds [5,6,7], trace amounts of peonidin- or pelargonidin-based anthocyanins have been identified in some cultivars [2]
Effect of different ethephon concentrations on anthocyanin accumulation In the present study, the function of ethylene as a preharvest elicitor of anthocyanin pigments was investigated in black carrots following foliar spray with ethephon
Summary
Black carrots (Daucus carota ssp. sativus var. atrorubens Alef.) constitute a valuable source of anthocyanins, which are used as natural red, blue and purple food colourants. Atrorubens Alef.) constitute a valuable source of anthocyanins, which are used as natural red, blue and purple food colourants. In mature black carrot taproots, acylated cyanidin glycosides represent the major fraction of anthocyanin compounds [5,6,7], trace amounts of peonidin- or pelargonidin-based anthocyanins have been identified in some cultivars [2]. Due to both increasingly rigorous legal restrictions and consumer concerns, there is increasing demand for natural food colourants that can be used as substitutes for synthetic colours [8, 9]. In addition to anthocyanin as the predominant polyphenol, black carrots contain large amounts of other phenolic compounds, such as hydroxycinnamates and caffeic acid [5]
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