Hormesis in the heavy metal accumulator plant Tillandsia ionantha under Cd exposure: Frequency and function of different biomarkers

Cadmium is one of the most biotoxic substances among all heavy metals, but an increasing number of studies indicate that low-dose Cd can induce hormesis in some plants. However, the frequency of hormesis in various biomarkers (molecular, resistance, and damage markers) and their associated function in hormesis-generation are poorly understood. In this study, the heavy metal accumulator plant Tillandsia ionantha Planch. was exposed to 5 mM CdCl2 with 6 different time periods. The trends of 18 biomarkers after Cd exposure were detected. The percentage for all non-monophasic responses based on dose-response modeling was higher (50 %), in which seven (38.89 %) biomarkers showed hormesis, indicating that hormesis effect can commonly occur in this plant. However, the occurrence frequency of hormesis in different types of biomarkers was different. Six Cd resistance genes, glutathione (GSH) among 6 resistance markers, and 0 damage markers showed hormesis. Factor analysis further showed that the 6 Cd resistance genes and GSH were positively intercorrelated in the first principal component. Therefore, heavy metal resistance genes and GSH may play an important role in the generation of hormesis. Our experiment shows that time-dependent non-monophasic responses, including hormesis, are activated by considerably high concentrations of Cd, presenting a strategy to cope with and potentially reduce the anticipated damage as the dose of stress increases over time.