Ce³⁺ induces flavonoids accumulation by regulation of pigments, ions, chlorophyll fluorescence and antioxidant enzymes in suspension cells of Ginkgo biloba L.

Abstract

Rare earth elements, a type of abiotic elicitor, were used to investigate the shift in the mechanism of flavonoid accumulation from primary metabolites in Ginkgo suspension cell culture. The changes in flavonoids, mineral ions, photosynthetic pigments, chlorophyll fluorescence and antioxidant enzymes with varying Ce³⁺ (Ce(NO₃)₃) doses (0.01–5.0 mM) were studied. Low doses of Ce³⁺ (0.01–0.1 mM) improved cell growth and the highest increased dry weight was 2.67 g L⁻¹ medium at 0.1 mM Ce³⁺ dose. Moderate doses (0.5–1.0 mM) limited cell growth and initiated a self-protective mechanism through modulation of the pigments, ions and flavonoid content, chlorophyll fluorescence and antioxidant enzymes, while high doses (2.0–5.0 mM) inhibited the cell growth and even caused cell mortality. The chlorophyll content, K⁺, Zn²⁺ and growth mass peaked at 0.1 mM Ce³⁺. The Fv/Fm, and Fv′/Fm′ values, and the amounts of P, Ca²⁺, Fe²⁺ and Zn²⁺ reached a maximum at 0.5 mM Ce³⁺ while the flavonoids content was highest at 1.0 mM Ce³⁺ (11.1 mg L⁻¹ medium). The antioxidant enzyme activities were high from 0.05 to 0.5 mM Ce³⁺. Moreover the changes of chlorophyll fluorescence images of the suspension cells were consistent with the cell growth, relative electrical conductivity (REC) and malondialdehyde (MDA) content with increasing Ce³⁺ doses. Our findings suggest doses of 0.1–0.5 mM Ce³⁺ in Ginkgo cells shifted the metabolism from primary to secondary processes, diverting the metabolism from growth to defense related pathways as a result of the flavonoids accumulation. The high ratio of Car/Chl t, high Car content and 0.5–1.0 mM Ce³⁺ were beneficial for the accumulation of flavonol glycosides in Ginkgo suspension cells.