Elicitor-mediated simultaneous accumulation of phloridzin and ursolic acid in Annurca apple peel-derived calli

Abstract

Background: Apple peel is rich in natural molecules, many exhibiting a significant bioactivity. In this study, our objective was to establish a novel callus line derived from the apple peel of the Italian local variety Annurca, known to accumulate high levels of dihydrochalcones and terpenes. In this regard, we tested the impact of one elicitor, yeast extract, on the expression of genes encoding key enzymes involved in phloridzin and ursolic acid biosynthesis, leading to the accumulation of these antioxidant compounds. We also assessed the bioactivity of callus extracts enriched in these phytochemicals.

Results: After the elicitation, data showed increased expression of genes directly related to the synthesis of phloridzin and ursolic acid that were found to accumulate within the cultures. This presumably could explain the remarkable activity of extracts from the elicited-calli in inhibiting the growth of Staphylococcus aureus and Bacillus cereus. Also, the extracts enriched in antioxidant compounds inhibited reactive oxygen species (ROS) production in human cells exposed to ultraviolet-A (UV-A) radiation.

Conclusion: Our results underscore the vast potential of the Annurca apple peel cell line in producing natural compounds that can be employed as food components to promote human health. © 2024 The Author(s). Journal of the Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Keywords: Rosaceae; callus cultures; dihydrochalcone; elicitor; foodborne pathogens; terpene.

Figure 1

Yeast extract (YE) effect on Annurca peel‐derived calli on (A) total polyphenol content (TPC) and (B) antioxidant activity %. Superscript letters indicate significant differences by Tukey's multiple comparison test (P< 0.05). CTRL indicates non‐elicited cultures whereas YE 300 and YE 500 indicate elicited cultures.

Figure 2

(A) Phloridzin pathway; (B) Yeast extract (YE) effect on the genes MdDH and MdUGT88F1, related to phloridzin biosynthesis in Annurca peel‐derived calli. The relative quantity of gene expression levels is defined as log₂RQ. Asterisks denote statistically significant differences of each treatment compared to the control samples that here are not shown (**P < 0.01; ***P < 0.001) by Student t‐test. YE 300 and YE 500 indicate the elicited cultures.

Figure 3

(A) Ursolic acid pathway; (B) Yeast extract (YE) effect on the genes MdCYP716A175 and MdOSC1, related to ursolic acid biosynthesis in Annurca peel‐derived calli. The relative quantity of gene expression levels is defined as log₂RQ. Asterisks denote statistically significant differences of each treatment compared to the control samples that here are not shown (*P < 0.05; **P < 0.01; ***P < 0.001) by Student t‐test. YE 300 and YE 500 indicate the elicited cultures.

Figure 4

Effect of Annurca peel‐derived callus extracts on cell survival. Dose–response curve of HaCaT cells incubated for 48 h with increasing concentrations (1–200 μg mL⁻¹) of control extract (black circles) and YE 500 extract (black squares).

Figure 5

Protective effect of Annurca peel‐derived callus extracts on UV‐A‐stressed HaCaT cells. Light pink bars refer to non‐elicited callus cultures, pink bars refer to cells incubated with control extract, and dark pink bars refer to cells incubated with elicited extract, in the absence (−) or in the presence (+) of UV‐A stress. Values are expressed as percentages compared to non‐elicited callus cultures. Student t‐test: *Indicates a statistical difference with respect to untreated cells (P < 0.05). ***Indicates a statistical difference with respect to UV‐A‐irradiated untreated cells (P < 0.005). Untreated indicates HaCaT cells without the addition of callus extract, whereas CTRL and YE 500 indicate HaCaT cells upon the addition of non‐elicited and elicited callus extract, respectively.