Effect of fluoride on the biosynthesis of catechins in tea [Camellia sinensis (L.) O. Kuntze] leaves

• F affects the content of polyphenols and catechins in the leaves of tea plants.
• F concentrations below 4 mg L−1 promote the biosynthesis of catechins in tea plants and up-regulated catechins biosynthetic enzymes activities.
• F concentrations more than 8 mg L−1 restrain tea plant growth and the synthesis of catechins.

Tea plant, Camellia sinensis, can accumulate high levels of fluoride (F); however, it is unclear how F influences secondary metabolism in tea plants. In this study, two tea cultivars seedlings, Fuyunliuhao (FY) and Wuniuzao (WNZ), were cultivated in nutrient solutions containing different concentrations of F for 4 weeks to investigate the effects of F on the content of catechins, the activity of related biosynthetic enzymes in the leaves. The content of tea polyphenols reached to the top at 2 mg L−1 (FY) or 4 mg L−1 (WNZ) and then decreased dose-dependently with the F concentration increasing; the content of catechins increased between 2 and 8 mg L−1 and decreased at 16 mg L−1 significantly comparing with the control; the activity of PAL, C4H, CHI and DFRm in WNZ, DFRm and DFRq in FY increased significantly at 4 mg L−1 F concentration comparing to the control and the activity of ANR in WNZ, C4H in FY decreased dose-dependently with the increasing F concentration, while the activity of PAL, CHI in FY changed little with the F concentration between 0 and 16 mg L−1. These results suggested that F concentrations lower than 4 mg L−1 promote the biosynthesis of catechins in tea plants by up-regulating the activity of related biosynthetic enzymes, whereas F concentrations more than 8 mg L−1 restrain tea plant growth and the synthesis of catechins. The pathways of catechins biosynthesis are tremendously complicated, and further research is required to determine whether F regulates the metabolism of tea catechins by altering other pathways and enzymes in addition to those analyzed in this study.