Changes in Quercetin Derivatives and Antioxidant Activity in Marigold Petals (Tagetes patula L.) Induced by Ultraviolet-B Irradiation and Methyl Jasmonate

Abstract

Marigold petals contain numerous antioxidative flavonoids and carotenoids that can be affected by environmental stressors. There is yet no detailed study on the relationship between phytochemical accumulation and stressors in marigold petals. This study evaluated quercetin derivatives and antioxidant activity in marigold petals in response to ultraviolet-B (UV-B) irradiation and methyl jasmonate (MeJA) treatment. The limiting UV-B radiation intensity and MeJA dose that caused no wilting damage under 1-h daily treatment for 10 days were <2 W∙m−2∙s−1 and <10 mM, respectively. Marigold petals contained three major flavonoids, quercetin-7-O-glucoside (Q7G, 6.6 mg∙g−1dw), quercetin-3-O-glucoside (Q3G, 62.7 mg), and quercetin (26.6 mg), possessing different antioxidant potential and exhibiting the highest power in quercetin and next value in Q7G. Single UV-B irradiation exerted a limited effect on the changes in the content of the three quercetin derivatives, whereas combined treatment with 1 W UV-B radiation and 5 mM MeJA resulted in the highest total quercetin content, showing >20% increase compared to that without treatment. This increase primarily resulted in an increase in quercetin content. MeJA treatment positively affected the increase in Q3G and Q7G contents in a dose-dependent manner during the 10-d experimental period but exerted no considerable effect on quercetin accumulation. The antioxidant activity was increased when flowers were exposed to mild MeJA treatment of 5−10 mM. UV-B irradiation decreased the antioxidant activity of marigold petals, but this decrease could be compensated by MeJA treatment.

Keywords: flavonoid; growth regulator; marigold flower; quercetin-3-O-glucoside; quercetin-7-O-glucoside; ultraviolet B.

Figure 1

Morphological appearance of marigold flowers treated with different UV-B intensities and MeJA concentrations for 10 days (A). Each row in (A) represents treatment with UV-B alone (without MeJA), MeJA alone (without UV-B), and treatment by MeJA concentration under UV-B 1 W·m⁻²·s⁻¹. Relative fresh weight of marigold flowers depending on UV-B intensities (B-1) and MeJA concentrations (with or without UV-B 1 W·m⁻²·s⁻¹) (B-2) treatment for 10 h within a day. The relative weight was expressed as the mean ± SE value of the weight of triplicate samples. Alphabetically small and different letters on graphs indicates significant differences in Tukey’s studentized test at p < 0.05.

Figure 2

HPLC chromatogram of quercetin derivatives in marigold petals; 1, Quercetin-7-O-glucoside (Q7G); 2, Quercetin-3-O-glucoside (Q3G); 3, Quercetin.

Figure 3

Quercetin derivatives content in marigold petals treated with MeJA (5 mM) or non-treatment depending on UV-B intensity (0, 1, 2, 4 W∙m⁻²∙s⁻¹) for 5 days. All data is exhibited using mean value ± standard deviation within three replications (n = 3). Different letters within bar graphs of each group (Q7G, Q3G, Quercetin, and Total) indicate significant differences by Tukey’s studentized test (HSD) at p < 0.05. Significant difference between non-MeJA and MeJA in each group was performed by Student’s t-test. ns, *, and ** indicate statistically non significance, significance at p < 0.05, and significance at p < 0.01, respectively.

Figure 4

Quercetin derivatives content in marigold petals treated with different MeJA concentrations with/without UV-B (1 W∙m⁻²∙s⁻¹) for 1 h/day × 1 day (short period treatment) (A) and 1 h/day × 10 days (long period treatment) (B). Correlation of individual flavonoids by treatment (C). Different letters within each group (Q7G, Q3G, and Quercetin) in (A,B) indicate significant differences by Tukey’s studentized test at p < 0.05. Significant difference between non-MeJA and MeJA in each group was performed by Student’s t-test. Correlation was performed with Pearson correlation coefficient test. Q7G, Quercetin-7-O-glucoside; Q3G, Quercetin-3-O-glucoside. Content of Q7G is expressed mg Q3G equivalents·g⁻¹ dry weight. All data is expressed mean ± standard deviation of three replications.

Figure 5

ABTS radical scavenging activity of marigold petals treated to series of MeJA concentration either without UV-B (A) or with 1 W∙m⁻²∙s⁻¹ UV-B (B) for 10 days. Antioxidant activities were expressed as mg VCE·g⁻¹ dry weight. VCE indicates vitamin C equivalents. Error bars on each graph indicates standard errors of triplicate samples. Statistical significance within treatment day was performed with Tukey’s studentized test (HSD) at p < 0.05.

Figure 6

Correlation between ABTS radical scavenging activity and content of quercetin derivatives in 10 mM MeJA treatment without UV-B (A) and with 1 W∙m⁻²∙s⁻¹ UV-B (B). ns, **, and *** indicate no significance, significance at p < 0.01, and significance at p < 0.001, respectively, in Pearson correlation coefficient test.