Figure 4 Electron-dense precipitates recovered from root cortical parenchymal cell of Festuca rubra and X-ray spectra of elements. Bar corresponds to 1,000 nm.

Insets JNK-IN-8 represent enlarged region where X-ray microanalyses have been performed. Bar corresponds to 200 nm. Ag peaks, at 23 keV, were well visible. The presence of C, Os, U and Pb was due to sample preparation, and Cu was due to the grids used as section support. Figure 5 Electron-dense precipitates recovered from leaf parenchymal cell of Medicago sativa and X-ray spectra of elements. Bar corresponds to 1,000 nm. Insets AC220 concentration represent enlarged region where X-ray microanalyses have been performed. Bar corresponds to 100 nm. Ag peaks, at 23 keV, were well visible. The presence of C, Os, U and Pb was due to sample preparation, and Cu was due to the grids used as section support. Figure 6 Electron-dense precipitates recovered from leaf parenchymal cell of Brassica juncea and X-ray spectra of elements. Bar corresponds to 1,000 nm. Insets represent enlarged region where X-ray microanalyses have been performed. Bar corresponds to 100 nm. Ag peaks, at 23 keV, were well visible. The presence of C, Os, U and Pb was due to sample preparation, and Cu was due to the grids used as section

support. Discussion Plants are able to take up silver, although this element has no biological functions [24]. The typical level of Ag in plant tissue is <1 ppm [25]. When the ionic form of Ag occurs in low concentrations in the soil, it accumulates check details evenly throughout the whole plant. At much higher concentrations, Ag accumulation increases in the plant roots, but it is poorly translocated to the shoots [26]. This also occurs when plants are grown in hydroponics. Our data

confirms the major Ag accumulation in plant roots. Also, we demonstrated how different Resveratrol the root-to-leaf Ag mobilization can be among different species. According to Harris and Bali [17], B. juncea and F. rubra are much more efficient than M. sativa in Ag uptake and translocation. TEM analyses confirmed the presence of AgNPs through all the plant tissues of the three species, in the form of single particles and/or intracellular clusters of different sizes and shapes. This fact suggests that after entering through the root apparatus, AgNPs are able to move to remote positions and to form aggregates throughout the plants. The movement probably occurs through the vascular system, but it is unclear whether particles were transported as nanosized individuals or as aggregates. Twenty-four hours after treatment, roots showed aggregates that appeared to be blocked to further movement at the plasmalemma of the cortical tissues, while isolated nanoparticles have been mainly found close to the root vascular core, in the xylem pits and in the vessel lumen.