Exploring lithium toxicity in rice: An in vitro study on morphological and biochemical parameters

Abstract

Lithium (Li) is a known emerging contaminant and its effects on plant growth and metabolism are not fully understood. Most of the studies have been conducted using soil as the medium or by using hydroponics. The present study explores how different concentrations of lithium affect growth, chlorophyll level, phenolic compound accumulation and Peroxidase (POD) activity in Oryza sativa L. under in vitro conditions.  Seeds were cultured on Woody Plant Medium (WPM) supplemented with lithium sulfate (Li₂SO₄) for 21 days. Chlorophyll a, b and total chlorophyll content were quantified and total phenolic content and POD enzyme activity were assessed to evaluate oxidative stress and metabolic changes. Morphological observations, including growth and symptoms of stress, were also recorded.  Chlorophyll a, b and total chlorophyll content showed an initial increase at lower lithium concentrations (1-2 mg/L), followed by a decline at (3-10 mg/L). In contrast, total phenolic content exhibited a consistent, dose-dependent increase, indicating progressive activation of oxidative stress pathways. POD enzyme activity peaked at 5 mg/L but declined at higher concentrations, likely due to enzyme inhibition under intensified stress conditions. Morphologically, lithium-treated plants displayed stunted growth, with pronounced stress symptoms such as browning of roots and stems at enhanced lithium levels of 3-10 mg/L. Growth inhibition at elevated lithium levels (2-10 mg/L) was evidenced by a reduction in biomass.