Abstract
Hg is an environmental pollutant with severe biotoxicity. Epiphytic Tillandsia species, especially Spanish moss T. usneoides, are widely used as the bioindicator of Hg pollution. However, the effects of different Hg concentrations on Tillandsia have been rarely studied and the occurrence of hormesis in Tillandsia species has not been determined. In this study, T. usneoides was subjected to stress induced by 15 concentrations of gaseous Hg ranging from 0 to 1.8 μg m–3 through a misting system and then Hg content and eight common biomarkers in leaves were measured. The results showed that leaf Hg content significantly increased with Hg concentration, showing a linear relationship. However, there were no obvious mortality symptoms, indicating that T. usneoides showed strong resistance to Hg. Conversely, there were no simple linear relationships between changes in various biomarkers following Hg treatment of T. usneoides and Hg concentration. With increasing Hg concentration, malondialdehyde (MDA) content did not change significantly, superoxide anion radical content decreased gradually, superoxide dismutase (SOD) content decreased to the bottom and then bounced back, electrical conductivity increased, and glutathione (GSH) and metallothionein (MT) content increased to the peak and then dropped. The coefficient of determination of the dose-effect curves between SOD, GSH, and MT contents and Hg concentration was high, and the dose-effect relationship varied with hormesis. The present study is first to confirm hormesis induced by heavy metal pollution in Tillandsia species.
Highlights
Hormesis is the phenomenon in which exposure to a low toxin dose produces stimulatory effects but that to a high toxin dose produces inhibitory effects on growth in the same organism (Calabrese and Blain, 2009)
The leaves turned yellow when Hg concentration increased to 1.0 μg m−3 (Figure 3B), and the yellowed area increased with increasing Hg concentration (Figure 3C)
T. usneoides was subjected to heavy metal stress induced by 15 different Hg concentrations
Summary
Hormesis is the phenomenon in which exposure to a low toxin dose produces stimulatory effects but that to a high toxin dose produces inhibitory effects on growth in the same organism (Calabrese and Blain, 2009). Tillandsia species can absorb moisture and nutrients from the air through their leaves Their leaves exhibit a strong absorption capacity for many atmospheric pollutants, heavy metals. Many studies have shown that Tillandsia species are effective indicators for monitoring atmospheric heavy metals based on the content of pollutants accumulated in their leaves (Wannaz et al, 2006; Vianna et al, 2011; Schreck et al, 2016, 2020; Sánchez-Chardi, 2016; Li et al, 2019). Studies on air pollution monitoring using Tillandsia species date back to the era when T. usneoides, known as Spanish moss, was identified to rapidly and effectively absorb Hg (Calasans and Malm, 1997). Hg accumulation and eight common biomarkers in leaves were measured to generate dose-effect curves and to explore the occurrence of hormesis in T. usneoides
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