Influence of Sodium Fluoride on Nitrate Reductase Inhibition and Physiological Changes in Plants

Abstract

Sodium fluoride (NaF) poses significant phytotoxic effects on plants, primarily through the inhibition of key metabolic processes. Fluoride is readily absorbed by plant leaves and roots, accumulating in metabolically active cells, particularly at leaf tips and margins. This accumulation leads to a spectrum of symptoms depending on species sensitivity and environmental factors. Fluoride concentrations vary across species, with resistant plants such as cotton and asparagus tolerating higher levels without visible injury, while sensitive species like Chenopodium murale exhibit severe toxicity even at low concentrations.

Fluoride exposure induces structural and functional changes in plant cells, resulting in chlorosis, necrosis, and ultimately reduced photosynthesis, growth, and yield. Severe fluoride toxicity can lead to plant death, with affected leaves containing significantly higher fluoride levels than healthy ones. Sodium fluoride inhibits nitrate reductase (NR) activity in vivo, a critical enzyme for nitrogen metabolism, while not affecting its activity in vitro. Additionally, fluoride disrupts various physiological processes, leading to stunted growth, diminished photosynthetic pigments, and impaired antioxidative enzyme activity. It also interferes with cell signalling and calcium dynamics, crucial for fertilization and overall plant development. The cumulative impact of sodium fluoride on seed germination and seedling growth underscores the need for further investigation into its ecological consequences and management strategies to mitigate its effects on agricultural productivity and plant health.