Table 1.
Details of plant species used for exogenous generation of silver NPs by root system of intact plants.
Figure 1.
Potential of root system of plants to reduce DCPIP (0.1 mM) and ferricyanide (1 mM).
Reduction of DCPIP (a–d) and ferricyanide (c–d) by root system of intact plants of Lycopersicon esculentum (Le), Brassica juncea (Bj), Vigna mungo (Vm), Cicer arietinum (Ca), Ocimum sanctum (Os), Catharanthus roseous (Cr), Cynodon dactylon (Cd), Cannabis sativa (Cs), Phyllanthus fraternus (Pf), Portulaca grandiflora (Pg), Triticum aestivum (Ta) and Vernonia cinerea (Vc) under non-sterile (a–c) and sterile (d) conditions. Ctrl represents 0.1 mM DCPIP. Vertical lines on bars represent mean ± standard error, n = 5. Values designated by different letters above bars are significantly different between plant species at p ≤ 0.05 level (Duncan's multiple range test).
Figure 2.
Potential of root system of intact plants to generate silver NPs.
Root system of intact plants of (a) Phyllanthus fraternus, (b) Portulaca grandiflora, (c) Triticum aestivum, (d) Amaranthus gracilis and (e) Vernonia cinerea exhibitingpotential to alter clear colorless AgNO3 of different concentrations (mM) turbid brown. No color change noted in the tubes containing different concentrations of AgNO3 incubated under similar conditions without plants (a–d).
Figure 3.
UV-Vis absorption spectra of 0.5, 1.0 and 2 mM AgNO3 exposed to root system of intact plants of different plant species for 12 h.
Figure 4.
TEM images (a–c), SAED (d–f) and EDX (g–i) of silver NPs synthesized exogenously by root system of intact plants of Tagetes erecta (a, d, g), Catharanthus roseous (b, e, h), Euphorbia hirta (c, f, i).
SAED show Bragg reflections characteristic of crystalline Ag0 () and Ag2O (*).
Figure 5.
TEM (a–c), SAED (d–f) and EDX (g–i) of silver NPs synthesized exogenously by roots system of intact plants of Brassica juncea (a, d, g), Cicer arietinum (b, e, h), and Phyllanthus fraternus (c, f, i).
SAED show Bragg reflections characteristic of crystalline Ag0 () and Ag2O (*).
Figure 6.
TEM (a–d), SAED (e–h) and EDX (i–l) of silver NPs synthesized exogenously by root system of intact plants of Cynodon dactylon (a, e, i), Portulaca grandiflora (b, f, j), Lycopersicon esculentum (c, g, k) and Vernonia cinerea (d, h, l).
SAED show Bragg reflections characteristic of crystalline Ag0 () and Ag2O (*).
Figure 7.
The PXRD pattern of silver NPs synthesized exogenously by roots system of intact plants of various plant species showing Bragg reflections characteristic of crystalline face-centred cubic structure of Ag0 () and cubic structure of Ag2O (*).
Figure 8.
Potential of sodium citrate and root system of intact plants of 4 day old Vigna mungo and Triticum aestivum to generate silver NPs.
1% sodium citrate (a) and root system of intact plants of V. mungo (b) and T. aestivum (c) incubated in AgNO3 of different concentrations (mM) for 6 h, showing alteration in color and turning clear solution colloidal under sterile conditions at room temperature. UV-Vis spectra of resultant colloidal solutions formed by 1% sodium citrate (d), V. mungo (e) and T. aestivum (f).
Figure 9.
TEM images (a–b), SAED (c–d), EDX (e–f) and PXRD (g–h) of silver NPs synthesized exogenously by root system of intact plants of Vigna mungo (a, c, e, g) and Triticum aestivum (b, d, f, h).
Bragg reflections characteristic of crystalline face-centred.
Figure 10.
Schematic representation of the mechanism involved in the reduction of Ag+ and formation of silver NPs at the root surface of live plants.
Figure 11.
Evidences demonstrating - the presence of dehydrogenases in association with root surface cells (a, b); and the potential of dehydrogenases to reduce triphenyltetrazolium to triphenylformazan and Ag+ to Ag0 (which in turn generate Ag0/Ag2O-nanoparticles) (c).
(a) and (b) displays root system of intact plants of Portulaca grandiflora incubated in phosphate buffer (pH 7.6) in absence (A) and presence of triphenyltetrazolium chloride (B) or AgNO3 (C). Note colour change due to formation of triphenylformazan (B) and silver-nanoparticles (C). (c) depicts tubes with reaction mixture (100 mM phosphate buffer pH 7.6) containing - root enzyme extract with NADH (D); root enzyme extract with triphenyltetrazolium chloride (E); root enzyme extract with triphenyltetrazolium chloride and NADH (F); AgNO3 with NADH (G); AgNO3 with root enzyme extract (H); and AgNO3 with root enzyme extract and NADH (I), 6 h after incubation at 37°C. Please note colour change due to formation of triphenylformazan (F) and silver nanoparticles (I). (d) shows silver nanoparticles from tube (I) formed due to dehydrogenase activity in presence of NADH. (e) depicts absorption spectra of the reaction mixtures from tubes (G), (H) and (I). Note silver nanoparticle specific absorption peak that intensified due to dehydrogenase activity in presence of NADH.
Table 2.
Dehydrogenase activities recorded at the surface of roots of intact plants (in vivo) and in root enzyme extracts (in vitro).