Recent Developments in Understanding Fluoride Accumulation, Toxicity, and Tolerance Mechanisms in Plants: an Overview

Abstract

Excess fluoride (F − ) inhibits the growth and metabolism of several crop plants, while some have an innate ability for F − tolerance. The present study was undertaken to explain how plants tolerate F − toxicity and understand the efficacy of exogenous stress protectants and phytoremediation approaches for F − homeostasis and tolerance of crop plants. This review comprehends existing information available so far on the F − accumulation toxicity and tolerance mechanisms. A high level of F − inhibits plant growth, water and nutrition uptake, enzyme activity, and yield. This review concludes that plants tolerate through F − homeostasis (exclusion, chelating, and compartmentalization) and gene activation for enhanced pathways of antioxidants, hormones, osmolytes, stress proteins, transporters, and metabolites. Exogenously applied stress protectants like salicylic acid (SA), polyamines (PAs), melatonin (Mel), glycine betaine, calcium (Ca 2+ ), and nanoparticles are differentially effective in reducing F − accumulation and toxicity by regulating various pathways. Application of minerals minimizes the F − accumulation through changing pH of soil, chelate formation with F − , and permeability of the cell membrane. Although many of the physiological aspects (enzyme activities, F − accumulation and regulation) were studied earlier, however, an effort has been made for the first time to understand the genetic basis and role of stress protectants and mineral nutrition, regulating these physiological activities, and explore new integrated approaches related to F − mitigation by means of phytoremediation. This review covers the recent development in F − transporters, gene expression, and biochemical and hormonal levels which could be utilized in regulating F − toxicity through omics and transgenic approaches in the future.

Fluoride mitigates aluminum-toxicity in barley: morpho-physiological responses and biochemical mechanisms

“…Fluoride (F − ) is a well-known pollutant in the environment for its highly reactive and non-biodegradable nature, which ranks 13 th in abundance in the Earth’s crust [ 21 , 22 ]. Most of the research findings in plants suggest that excessive accumulation of fluoride causes phytotoxicity [ 21 ]. However, fluoride at low concentrations is beneficial in the prevention of dental caries and facilitates the mineralization of hard tissues.…”

Bioaccumulation of Fluoride in Plants and Its Microbially Assisted Remediation: A Review of Biological Processes and Technological Performance

“…Fluoride is a common phytotoxic contaminant for plants [190]. Plant species absorb fluoride from water and soil via roots and air through leaves [190,191], accumulate fluoride in different parts of the plant, and acquire fluoride at a higher level than in the environment [192,193]. Fluoride accumulation in plants depends on various factors such as fluoride concentration in soil, plant species, and soil properties [178].…”

“…The minimal optimal limit for fluoride accumulation in plants is 10 mg L −1 ; however, fluoride uptake levels in Trifolium repens and Lolium multiflorium were 30 mg kg −1 and 50 mg kg −1 [197]. Therefore, it has been reported that fluoride toxicity can adversely impact seed germination, cellular enzymatic activity, crop yield, etc., as shown in Table 1 [191,[198][199][200][201][202]. Shoot tip burning and chlorosis, reduction in abscisic acid, and inhibition of polyamine biosynthesis and the ascorbate-glutathione cycle [206] Rice (Oryza sativa)…”

“…After that, fluoride diffuses from the plants through stomata [1]. Although some plant species have an inherent ability to tolerate fluoride, the growth and metabolism of numerous crop species are inhibited by excessive fluoride [191]. Biochemical, physiological, and molecular alterations could occur in plants because of prolonged contact with fluoride [209].…”

“…Fluoride accumulation in plants is a significant risk, affecting their growth and development [196]. It enters into plants through water, soil, or leaves [191]. Plants may undergo biochemical, physiological, and molecular changes due to continuous fluoride exposure [209].…”