Cadmium uptake, cellular localization and structural and physiological effects in Pteris vittata.

This study aimed to provide new information about the effects of different concentrations of cadmium (30, 60, 100 µM) on the fern Pteris vittata. Taking into account the root system, our results showed, at the increase of Cd concentrations, a significant progressive reduction of the meristematic region size, probably related to the inhibition of mitotic activity. Moreover, there was an increase in length and in density of roots hairs, and an acropetal shift of their development in plants treated with 30 and 60 µM Cd, while in plants treated with 100 µM there was a decrease of both length and density of roots hairs and a basipetal shift of their development in respect to control. The observed increase of root hairs was linked to an ectopic pattern of several hair cell formation. The quantitative analysis of cadmium content in roots and fronds of P. vittata, performed by the atomic absorption spectrophotometer, showed that the translocation of cadmium from the roots to the fronds depended on the time of exposure to Cd. The dithizone technique revealed the presence of Cd as reddish precipitates inside root hairs and in different tissues of the fronds, in particular in the indumentum. Thricomes and scales, probably play an important role in accumulating and then eliminating the excess of cadmium ions. Our results showed that P. vittata can efficiently absorb Cd from the solution, transport it to the fronds and accumulate it in the aboveground biomass. Cadmium can induce some sign of stress in the fronds of P. vittata, such as high lipid peroxidation and membrane leaching. Moreover, a significant decrease in relative water content and chlorophyll total content was detected in all the treated plants after fifteen days of exposure to Cd. Our results clearly indicated an involvement of enzymatic and non-enzymatic antioxidative systems in stress defence, however, only sufficient in 30 and 60 µM Cd treated plants to maintain a level of H2O2 not significantly different from control plants. Our results suggest that, in our experimental conditions, 60 µM Cd may represent the highest concentration that P. vittata can tolerate, as this Cd level improves the absorbance features of the root and allows a good transport and accumulation of the metal in the fronds. This threshold of tolerance is further confirmed from the study of the oxidative stress induced by Cd in P. vittata and by the antioxidant response of the plant. These results could represent a starting point for the development of strategies for the phytoremediation of sites contaminated with Cd.