Foliar application of yeast extract mitigates water deficit stress and elicits hypericin and phenolic production in Hypericum perforatum L

Abstract

Yeast extract has emerged as a bio-elicitor capable of modulating secondary metabolism and stress tolerance in plants, but its impact on St John's Wort (Hypericum perforatum L.) remains unexplored. Therefore, the interactive effects of yeast extract (0, 3, and 6 g L^-1) and irrigation intervals (7, 10, and 13 days) on hypericin and phenolic production in this medicinal herb were investigated in a field experiment. The prolonged irrigation intervals decreased biomass during both seasons. Hypericin content peaked under the 10-day irrigation interval but declined in the 13-day irrigation interval. Foliar spraying of yeast extract improved biomass, chlorophyll a, b, carotenoids, relative water content, and hypericin concentration across all water regimes. Yeast extract application reduced hydrogen peroxide and malondialdehyde contents in water deficit-subjected plants due to increased activity of superoxide dismutase and catalase, and elevated levels of total phenol and flavonoid contents in the leaves. The highest contents of hypericin and phenolics were recorded with applying 6 g L^-1 yeast extract under the 10-day irrigation interval, corresponding with the strongest 2,2-diphenylpicrylhydrazyl scavenging activity and ferric-reducing power in the leaves. These findings suggest that yeast extract spraying might be a promising approach for enhancing the productivity and quality of medicinal plants under water deficit.

Keywords: Antioxidant enzymes; DPPH; Drought stress; FRAP; Phenolics; St john’s wort.

Fig. 1

The effect of foliar-applied yeast extract (0, 3, and 6 g L⁻¹) on the biomass of Hypericum perforatum in two harvests (A, B) under various irrigation intervals (7, 10, and 13 days). Values with the same letter have no significant difference at P ≤ 0.05 based on Duncan’s multiple-range tests.

Fig. 2

The effect of foliar-applied yeast extract (0, 3, and 6 g L⁻¹) on the relative water content of Hypericum perforatum under various irrigation intervals (7, 10, and 13 days). Values with the same letter have no significant difference at P ≤ 0.05 based on Duncan’s multiple-range tests.

Fig. 3

The impact of foliar-applied yeast extract (0, 3, and 6 g L⁻¹) on chlorophyll a (A), chlorophyll b (B), and carotenoid (C) contents in leaves of Hypericum perforatum under various irrigation intervals (7, 10, and 13 days). Values with the same letter have no significant difference at P ≤ 0.05 based on Duncan’s multiple-range tests.

Fig. 4

The impact of foliar-applied yeast extract (0, 3, and 6 g/L) on H₂O₂ (A) and MDA (B) contents in leaves of Hypericum perforatum under various irrigation intervals (7, 10, and 13 days). Values with the same letter have no significant difference at P ≤ 0.05 based on Duncan’s multiple-range tests.

Fig. 5

The impact of foliar-applied yeast extract (0, 3, and 6 g L⁻¹) on SOD (A), CAT (B), and APX (C) activity in leaves of Hypericum perforatum under various irrigation intervals (7, 10, and 13 days). Values with the same letter have no significant difference at P ≤ 0.05 based on Duncan’s multiple-range tests.

Fig. 6

The impact of foliar-applied yeast extract (0, 3, and 6 g L⁻¹) on hypericin content in leaves of Hypericum perforatum under various irrigation intervals (7, 10, and 13 days). Values with the same letter have no significant difference at P ≤ 0.05 based on Duncan’s multiple-range tests.

Fig. 7

The impact of foliar-applied yeast extract (0, 3, and 6 g L⁻¹) on TPC (A) and TFC (B) in leaves of Hypericum perforatum under various irrigation intervals (7, 10, and 13 days). Values with the same letter have no significant difference at P ≤ 0.05 based on Duncan’s multiple-range tests.

Fig. 8

The impact of foliar-applied yeast extract (0, 3, and 6 g L⁻¹) on DPPH scavenging capacity (A) and FRAP (B) in leaves of Hypericum perforatum under various irrigation intervals (7, 10, and 13 days). Values with the same letter have no significant difference at P ≤ 0.05 based on Duncan’s multiple-range tests.

Fig. 9

Heat map based on Pearson’s correlation coefficient correlations between all variables in Hypericum perforatum L. Strong positive and negative correlations are represented by dark red and dark blue colors, respectively. The investigated variables include: biomass in harvest 1, 2 (biomass1, 2), hypericin in harvest 1, 2 (hypericin 1, 2), chlorophyll a, b contents (Chl a, Chl b), malondialdehyde content (MDA), hydrogen peroxide concentration (H₂O₂), Ascorbate peroxidase (APX), Catalase activity (CAT), superoxide dismutase activity (SOD), total phenol content (TPC), total flavonoid content (TFC), DPPH scavenging capacity (DPPH) and ferric reducing antioxidant power (FRAP). The correlation heat map based on the Pearson correlation coefficient was performed using R software (version: 3.5.0, http://www.r-project.org).

Fig. 10

Visualization of the interactions between treatments and variables via a hierarchically clustered heat map. Please see the abbreviation of variables in the capture of Fig. 8. The treatments were included: control (Y0-I7), 3 g L⁻¹ yeast extract + 7-day irrigation interval (Y3- I7), 6 g L⁻¹ yeast extract + 7-day irrigation interval (Y6- I7), without yeast extract + 10-day irrigation interval (Y0- I10), 3 g L⁻¹ yeast extract + 10-day irrigation interval (Y3- I10), 6 g L⁻¹ yeast extract + 10-day irrigation interval (Y6- I10), without yeast extract + 13-day irrigation interval (Y0- I13), 3 g L⁻¹ yeast extract + 13-day irrigation interval (Y3- I13), 6 g L⁻¹ yeast extract + 13-day irrigation interval (Y6- I13). A hierarchical cluster analysis (HCA) between treatments and variables were performed using R software (version: 3.5.0, http://www.r-project.org).