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Hydroponics: A Versatile System to Study Nutrient Allocation and Plant Responses to Nutrient Availability and Exposure to Toxic Elements
Published on: July 13, 2016
The analysis of changes in antioxidant enzyme activity and gene expression caused by lead contamination in Azolla
Mozhgan Mehtari1, Majid Talebi1, Badraldin Ebrahim Sayed Tabatabaei1
1Department of Biotechnology, College of Agriculture, Isfahan University of Technology, Isfahan, Iran.
Abstract:
Heavy metal contamination in aquatic ecosystems poses serious environmental and health risks. Azolla caroliniana, a promising candidate for phytoremediation, has the potential to absorb heavy metals like lead (Pb). However, limited information is available on the enzymatic and genetic responses of A. caroliniana under Pb stress. This study investigates the plant's phytoremediation capacity by analyzing antioxidant enzyme activity and gene expression under lead (II) acetate [Pb(C2H3O2)2] concentrations (0, 500, 750, 1,000 µM) over three time points (days 2, 4, and 6). The results showed that with increasing Pb concentration, antioxidant enzyme activity increased. Chlorophyll content increased by 25% at 1,000 µM Pb, whereas carotenoid and anthocyanin levels decreased by 233% and 30%, respectively. Total protein content declined by 90%. Additionally, SOD and CAT activities increased by 28%, while APX activity rose by 25%. Gene expression analysis revealed that genes associated with antioxidant enzymes CAT (94% decrease), APX (64% decrease), SOD (40% decrease), GR (8% increase), and PPO (93% decrease) as well as anthocyanin biosynthesis genes C4H (56% decrease) and CHS (87% decrease) were significantly downregulated at the highest Pb concentration in the later stages, indicating a critical adaptation phase. Observed gene expression fluctuations in the later stages may result from A. caroliniana's dynamic stress response, where initial upregulation of antioxidant defense genes suggests an attempt to mitigate oxidative stress, followed by metabolic adjustments leading to variations in gene expression levels. Lead uptake peaked on day 2 but significantly declined by 42% on day 6, likely due to cellular saturation, activation of detoxification mechanisms, or lead translocation into the growth medium. These findings highlight the potential of A. caroliniana as an effective phytoremediator for Pb-contaminated water bodies.
