Absorption and translocation to the aerial part of magnetic carbon-coated nanoparticles through the root of different crop plants

Abstract

The development of nanodevices for agriculture and plant research will allow several new applications, ranging from treatments with agrochemicals to delivery of nucleic acids for genetic transformation. But a long way for research is still in front of us until such nanodevices could be widely used. Their behaviour inside the plants is not yet well known and the putative toxic effects for both, the plants directly exposed and/or the animals and humans, if the nanodevices reach the food chain, remain uncertain. In this work we show that magnetic carbon-coated nanoparticles forming a biocompatible magnetic fluid (bioferrofluid) can easily penetrate through the root in four different crop plants (pea, sunflower, tomato and wheat). They reach the vascular cylinder, move using the transpiration stream in the xylem vessels and spread through the aerial part of the plants in less than 24 hours. Accumulation of nanoparticles was detected in wheat leaf trichomes, suggesting a way for excretion/detoxification. This kind of studies is of great interest in order to unveil the movement and accumulation of nanoparticles in plant tissues for assessing further applications in the field or laboratory.

Figure 1

TEM images at 300 kV using the cs image corrector (CEOS). a) Nanoparticles encapsulated in several layers of graphitic carbon, and surrounded by amorphous carbon. b) Detail showing the atomic planes of the nanoparticle metallic core.

Figure 2

Schematic representation of the Petri dish rizhotron with the four crops: a) pea; b) sunflower; c) tomato; d) wheat. Squares indicates sampling points of plant tissues.

Figure 3

Longitudinal sections of roots of pea (a, d), sunflower (b, e) and wheat (c, f). Arrows indicate accumulation of bioferrofluid in the cells. *, xylem containing ferrofluid; #, parenchimatic cell containing ferrofluid; p, parenchimatic cells; x, xylem vessels. Scale bars: a) and f), 50 μm; b) and e), 100 μm; c) and d), 25 μm.

Figure 4

Sections from different samples of the aerial parts of pea (a,e,i,l,o,r), sunflower (b,f,j,m,p,s), tomato (c,g,k,n) and wheat (d,h,q,t). a) Detail of the crown of pea after 24 h of exposure to bioferrofluid. b) Idem in sunflower. c) Idem in tomato. d) Crown of wheat after 24 h of exposure, showing an intense accumulation of bioferrofluid in tissues. e) Detail of the crown of pea after 48 h of exposure to bioferrofluid. f) Idem in sunflower. g) Idem in tomato. h) Detail of a longitudinal section in wheat after 48 h of exposure to bioferrofluid. i) Detail of a cross section of the first internode of pea after 24 h of exposure to bioferrofluid. j) Idem in sunflower. k) Idem in tomato. l) Detail of a cross section of the first internode of pea after 48 h of exposure to bioferrofluid. m) Idem in sunflower. n) Idem in tomato. o) Detail of a cross section of the second internode of pea after 24 h of exposure to bioferrofluid. p) Idem in sunflower. q) Detail of a longitudinal section of the second internode in wheat after 24 h of exposure to bioferrofluid. r) Detail of a cross section of the second internode of pea after 48 h of exposure to bioferrofluid. s) Idem in sunflower. t) Detail of a longitudinal section of the second internode in wheat after 48 h of exposure to bioferrofluid. Scale bars represent 100 μm, except in g), q) and t) whereas it represents 50 μm. Arrows indicate accumulation of nanoparticles in vascular tissues in a-c), f), i-t), and in cortical cells in e), g), h). Arrowheads indicate accumulation of nanoparticles in cortical cells in a), l), r), and in trichomes in q). Asterisks (*) indicate localization of vascular bundles.

Figure 5

Sections from a pea petiole (a), wheat leaf (b), and pea (c), sunflower (d) and tomato (e) roots. a) Detail of a cross section of a petiole from the first internode of pea after 24 h of exposure to bioferrofluid. Arrows indicate accumulation of nanoparticles in vascular tissues. b) Detail of a longitudinal view of wheat leaf showing accumulation of bioferrofluid in trichomes. c) Detail of a longitudinal section of a root of pea not immersed into the bioferrofluid and after 48 h of exposure to bioferrofluid of opposite roots. Arrows indicate accumulation of nanoparticles in vascular tissues. d) Idem in sunflower. e) Idem in tomato. *, xylem containing ferrofluid; #, parenchimatic cell containing ferrofluid; p, parenchimatic cells; x, xylem vessels. Scale bars represent 100 μm, except in d) whereas it represents 50 μm.