Abstract
In the present work, we investigated the response to Cd in Leptodictyum riparium, a cosmopolitan moss (Bryophyta) that can accumulate higher amounts of metals than other plants, even angiosperms, with absence or slight apparent damage. High-performance liquid chromatography followed by electrospray ionization tandem mass spectrometry of extracts from L. riparium gametophytes, exposed to 0, 36 and 360 µM Cd for 7 days, revealed the presence of γ-glutamylcysteine (γ-EC), reduced glutathione (GSH), and traces of phytochelatins. The increase in Cd concentrations progressively augmented reactive oxygen species levels, with activation of both antioxidant (catalase and superoxide dismutase) and detoxifying (glutathione-S-transferase) enzymes. After Cd treatment, cytosolic and vacuolar localization of thiol peptides was performed by means of the fluorescent dye monochlorobimane and subsequent observation with confocal laser scanning microscopy. The cytosolic fluorescence observed with the highest Cd concentrations was also consistent with the formation of γ-EC-bimane in the cytosol, possibly catalyzed by the peptidase activity of the L. riparium phytochelatin synthase. On the whole, activation of phytochelatin synthase and glutathione-S-transferase, but minimally phytochelatin synthesis, play a role to counteract Cd toxicity in L. riparium, in this manner minimizing the cellular damage caused by the metal. This study strengthens previous investigations on the L. riparium ability to efficiently hinder metal pollution, hinting at a potential use for biomonitoring and phytoremediation purposes.
Highlights
Trace metals, such as Cd, Hg, Pb, Cr(VI), etc., are important environmental pollutants, in areas characterized by a strong anthropogenic pressure [1]
reactive oxygen species (ROS) Production and Antioxidant Response to Cd In Cd-treated gametophytes, the amount of ROS highly increased compared to controls (Figure 1a), and the antioxidant/detoxifying enzymes under investigation were progressively activated by the two Cd concentrations
The GSH levels progressively decreased with the increase in Cd concentrations (Figure 3), and the γ-EC levels showed an upward trend between the controls and the 36-μM-treated samples, whereas the difference was significant between the control and the 360 μM CdCl2-treated samples (Figure 3)
Summary
Trace metals, such as Cd, Hg, Pb, Cr(VI), etc., are important environmental pollutants, in areas characterized by a strong anthropogenic pressure [1]. Cd can activate or even inhibit several antioxidant enzymes, such as superoxide dismutase (SOD; EC 1.15.1.1), which catalyzes the production of O2 and H2O2 from the radical anion superoxide (O2–); catalase (CAT; EC 1.11.1.6), which decomposes H2O2 into O2 and H2O, and many others Among these enzymes, the multifunctional enzyme glutathione-S-transferase (GST; EC 2.5.1.18) [9] can simultaneously counteract oxidative stress by enhancing ROS quenching, and detoxify a number of electrophilic xenobiotics or chemical elements, including Cd, both in yeast [10] and in plants [11,12,13]. Time course experiments with MCB can be monitored by confocal laser scanning microscopy (CLSM)
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