In particular, the role of plant metabolism is not yet understood

in any depth. The first experimental evidence of the synthesis of MeNPs in living vascular plants was reported by Gardea-Torresdey et al. [12] who observed the formation of Au nanoparticles of different sizes and structures in plants of Medicago sativa (alfalfa) grown on agar medium enriched with AuCl4. Brassica juncea (Indian mustard) was the second species in which the synthesis of MeNPs was studied [13, 14]. Besides alfalfa and Indian mustard, some other plant species have been tested for the capacity to synthesize MeNPs [6, 15]. One of the key questions Sapitinib order regarding this process is whether MeNP synthesis occurs outside the plant tissues with MeNPs transported through the root membrane into the plant or whether MeNPs are formed within plants by the reduction of the metal, previously taken up in ionic form by the roots. At present, the second hypothesis is the most accepted one. Plant-mediated MeNP formation was demonstrated by Sharma et al. [16] using XANES SC79 concentration and EXAFS, which provided evidence of Au reduction and the formation of AuNPs within the tissues of Sesbania drummondii. Interspecific differences (M. sativa vs. B. juncea) in the synthesis of MeNPs in response to experimental parameters such as Ag exposure time and concentration have been highlighted by Harris and Bali [17]. Finally, Starnes et

al. [18] studied the effects of managing some environmental parameters (e.g. temperature and photosynthetically

active radiation regime) on the nucleation and growth of AuNPs in some plant species, demonstrating empirical evidence on the feasibility of in planta NP engineering in order to produce nanomaterials of a wide variety of sizes and shape, which therefore have PDK4 different physical and chemical properties. The aims of our work were (i) to confirm the in vivo formation of silver nanoparticles (AgNPs) in B. juncea, M. sativa and Festuca rubra and (ii) to observe the location of AgNPs in plant tissues and cells in order (iii) to evaluate the possible relationship with plant metabolites. Methods Seed germination and plant growth Seeds of Indian mustard (B. juncea cv. Vittasso), red fescue (F. rubra) and alfalfa (M. sativa cv. Robot), previously washed with 1% H2O2 for 15 min and subsequently rinsed with deionized water, were placed in the dark in Petri dishes containing germinating paper and distilled water. Fifteen days after germination, the seedlings were transferred to a hydroponic system (1-L pots) containing a half-strength modified aerated Hoagland’s solution. The nutrient solution was replaced every 7 days. The plants were grown for a cycle of 30 days on a laboratory bench lit by fluorescence lamps providing an average photosynthetically active radiation (PAR) at the top of the plants of 500 μmol m−2 s−1 with a 16:8-h (light/dark) photoperiod. Ambient temperature was maintained at 22°C ± 2°C.