Analysis of nickel concentration profiles around the roots of the hyperaccumulator plant Berkheya coddii using MRI and numerical simulations

Abstract

Investigations of soil-root interactions are hampered by the difficult experimental accessibility of the rhizosphere. Here we show the potential of Magnetic Resonance Imaging (MRI) as a non-destructive measurement technique in combination with numerical modelling to study the dynamics of the spatial distribution of dissolved nickel (Ni 2+ ) around the roots of the nickel hyperaccumulator plant Berkheya coddii. Special rhizoboxes were used in which a root monolayer had been grown, separated from an adjacent inert glass bead packing by a nylon membrane. After applying a Ni 2+ solution of 10 mg l −1 , the rhizobox was imaged repeatedly using MRI. The obtained temporal sequence of 2-dimensional Ni 2+ maps in the vicinity of the roots showed that Ni 2+ concentrations increased towards the root plane, revealing an accumulation pattern. Numerical modelling supported the Ni 2+ distributions to result from advective water flow towards the root plane, driven by transpiration, and diffusion of Ni 2+ tending to eliminate the concentration gradient. With the model, we could study how the accumulation pattern of Ni 2+ in the root zone transforms into a depletion pattern depending on transpiration rate, solute uptake rate, and Ni 2+ concentration in solution.

Identification of chelidonic acid as the predominant ligand involved in Ni uptake in the hyperaccumulator Berkheya coddii

“…23 The concentration of chelidonic acid in leaves of B. coddii is approximately 10-fold higher compared to other plant sections (Table 3) indicating that the primary location of the acid is within the leaves. Reported chelidonic acid concentrations in leaves, stems and root of non-hyperaccumulators are <200 mg kg -1 indicating that it plays a role in the hyperaccumulation process.…”

“…21 Contradicting results were reported from studies using magnetic resonance imaging (MRI) on the roots, with results indicating a passive uptake mechanism and a specific pattern of Ni concentration at the plane of the roots. 22 Robinson et al 23 reported that the higher the content of Ni in the soil, the lower uptake of macro and micronutrients in the plant. Studies involving the effects of Ni uptake on insects were also investigated.…”

Sensing Technologies for Precision Phenotyping in Vegetable Crops: Current Status and Future Challenges

“…With this technology, 3D acquisition can be accomplished to acquire information on plant morphology with high precision; in particular, this approach has been appreciated for imaging roots in the root zone [61]. NMR is also used for the detection of water and labeled molecule fluxes within plant organs [62][63][64].…”

Root distributions in a laboratory box evaluated using two different techniques (gravimetric and image processing) and their impact on root water uptake simulated with HYDRUS

“…A thinner root zone layer may also be analyzed. Our box thickness was the same as in the study by Moradi et al (2010). Thinner boxes were used for example by Whiting et al (2000) 2 cm, Rudolph et al (2012) 0.5 cm, and Youssef and Chino (1988) 1 mm.…”

“…thickness, transparency etc. ), roots can be either directly photographed or the neutron, x-ray computed tomography, NMR, 2D light transition imaging technique can be applied (de Dorlodot et al, 2007;Doussan et al, 2006;Garrigues et al, 2006;Moradi et al, 2009Moradi et al, , 2010Moradi et al, , 2013Moran et al, 2000;Oswald et al, 2008;Rudolph et al, 2012Rudolph et al, , 2013Rudolph-Mohr et al, 2014;Stingaciu et al, 2013). These techniques were mostly applied to analyze root development in the early stage of plant and roots growth.…”