Specific stress responses to cadmium, arsenic and mercury appear in the metallophyte Silene vulgaris when grown hydroponically

Abstract

The tolerance of the metallophyte Silene vulgaris, a plant suitable for the phytostabilisation of metal(loid)-contaminated soils, to arsenic (As), mercury (Hg) and cadmium (Cd) was evaluated in a semi-hydroponic culture system under controlled environmental conditions. The appearance of oxidative stress, alteration of photochemical processes and modification of biothiol content were studied as physiological parameters of metal(loid) stress in plants treated with 0, 6 and 30 μM (As, Hg or Cd) for 7 days. In spite of the metal(loid) excluder behaviour of S. vulgaris, Cd was translocated to the aerial part of the plant at a higher rate than Hg or As. The major toxic effects were observed in roots, where lipid peroxidation was increased in a dose-dependent manner. Redox enzymes such as glutathione reductase (GR) were severely inhibited by Hg, whereas GR was overexpressed. The accumulation of Cd produced a remarkable production of phytochelatins (PCs) in roots, whereas Hg and As led to modest PCs synthesis. There was a severe loss of chlorophyll content in Cd-treated plants, accompanied with a significant decrease in photosystem II efficiency (ΦPSII) and photochemical quenching (qP). Similar negative effects were observed in Hg- and As-exposed plants, but to a lesser degree. The exposure to the highest dose of each toxic element (30 μM) caused depletion of the light harvesting complex b1 protein. In conclusion, specific stress signatures to each metal(loid) were observed, with As being the least toxic element, suggesting that different mechanisms of tolerance were exerted. These results could be applied in future experiments to select tolerant ecotypes to optimize the phytostabilisation of metal(loid) multipolluted soils.