An Original Mechanistic Study of Fluoride Hyperaccumulation in Tea Plants (Camellia sinensis) and Its Phytoremediation Implications for Fluoride-Contaminated Soils in Nigeria

Fluoride toxicity from geogenic and industrial sources affects substantial areas of Northern Nigerian soils, and the mechanistic basis for fluoride hyperaccumulation in plants, with particular reference to the unique case of Camellia sinensis, has potential implications for fluoride phytoremediation that have not been explored for Nigerian applications. This study conducted an original mechanistic investigation of fluoride uptake, translocation, and sequestration in Camellia sinensis grown in hydroponic and pot culture systems at fluoride concentrations of 0, 50, 100, 200, and 400 mg/L, and evaluated its potential application for phytoremediation of fluoride-contaminated soils collected from areas near Nigerian ceramic and aluminium processing facilities in Kogi and Niger States. Fluoride accumulation in roots, stems, and leaves was quantified by ion-selective electrode potentiometry at 14-day intervals. Translocation factor and bioconcentration factor were calculated. Fluoride speciation in leaf tissue was investigated using X-ray absorption near-edge structure (XANES) spectroscopy. Transcriptome analysis by RNA-Seq was conducted on root tissue to identify differentially expressed genes associated with fluoride tolerance and transport. Bioconcentration factors exceeded 15 in leaf tissue at all treatment concentrations, confirming hyperaccumulator status. XANES analysis revealed that fluoride was sequestered primarily as fluoroaluminium complexes in leaf cell vacuoles. RNA-Seq identified 847 significantly upregulated genes in fluoride-treated roots, including 12 novel aluminium-activated citrate transporter genes not previously associated with fluoride tolerance. An original mechanistic model of fluoride-aluminium co-transport is proposed. The study constitutes an original contribution to the molecular physiology of fluoride hyperaccumulation and provides a scientifically grounded rationale for field-scale phytoremediation trials in fluoride-contaminated Nigerian soils.

Keywords: fluoride hyperaccumulation, Camellia sinensis, phytoremediation, XANES spectroscopy, fluoride-contaminated soils