Determining the fluxes of Tl+ and K+ at the root surface of wheat and canola using Tl(I) and K ion-selective microelectrodes

Abstract

The objectives of this study were to develop and evaluate a Tl + ion-selective microelectrode (ISME) and to determine the basis for observed differences in Tl accumulation by durum wheat (Triticum turgidum L. var 'Kyle') and spring canola (Brassica napus L. cv 'Hyola 401'). Seedlings were grown hydroponically and fluxes of K + and Tl + were measured at the root surface in solutions containing 5 μM Tl + or 3 mM K + . After testing two different Tl (I) ionophores, a functional Tl + ISME was developed from calix[4]arene tetra-n-propyl ether which had a detection limit of 2.5 µM and a slope of 56.6 mV/dec. Measurements of Tl + flux indicate that Tl + efflux occurred within 300-500 µm of the root tip, and influx farther from the root tip. Compared with canola, wheat had a slightly larger region of efflux and a smaller region of maximal influx, resulting in flux per root branch that was 2.3 to 4 times greater in canola than in wheat. The magnitude and pattern of K + fluxes by the two species were more similar. Our results indicate that observed differences in Tl accumulation by wheat and canola are due both to differences in the magnitude of Tl flux per root branch of these species, and to differences in root morphology resulting in more root tips in canola than in wheat roots. Keywords Root morphology . Physiology . Competition . Trace element . Ion uptake Abbreviations ASET automated scanning electrode technique DBP dibutyl phthalate DBS dibutyl sebecate DBzDA18C6 dibenzyldiaza-18-crown-6 HDPE high density polyethylene ISE ion-selective electrode ISME ion selective microelectrode K, Tl, Me sum of all possible species of potassium, thallium, or other element, respectively K + , Tl + , Me z+ free ionic forms of potassium, thallium, or other element, respectively NaTPB sodium tetraphenylborate o-NPOE o-nitrophenol octyl ether PVC polyvinyl chloride SIET scanning ion electrode technique Plant Soil (2010) 335:299-310

When are metal complexes bioavailable?

“…A diffusive limitation is usually identified by comparing the metal internalisation flux with the calculated maximum diffusive flux. [14,61,63] Diffusive limitation can also be inferred from fluxes determined by the diffusive gradients in thin films (DGT) technique, [64] from free-metal-ion gradients close to biological surfaces, as measured by microelectrode arrays, [65,66] or from changes in biouptake under different flow conditions. [64,67,68] In the environment, a mass transport limitation (and thus potential contribution of labile complexes) is often observed: (i) for very low concentrations of metals (picomolar to nanomolar levels) [14,61,64] ; (ii) in constrained media such as sediments, soils or biofilms, where metals have much lower diffusion coefficients [69] ; or (iii) for nutrients and metals with high biouptake fluxes (e.g.…”

Toxicity of metals to roots of cowpea in relation to their binding strength

“…Second, some metals (i.e., Ag, Cs, and Tl) are substantially more toxic than the proposed minimum level, suggesting that additional factors contribute to their toxicity. Both Cs [18] and Tl [19,20] interfere with K uptake and metabolism due to their similar ionic properties (charge, ionic radius, etc.). Indeed, an increase in K concentration has been reported to decrease Cs toxicity [18].…”

Plant species and growing season weather influence the efficiency of selenium biofortification

“…Plant species differ in their ability to take up and assimilate Se (Terry et al 2000). Differences in root morphology and biochemical or physiological pathways are associated with different rates of uptake (Berkelaar and Hale 2000;Harskamp et al 2010). The sulphur (S)-rich Brassica species tend to accumulate higher concentrations of Se than other species due to the biosynthesis of glucosinolate (Bañuelos et al 2007;Harskamp et al 2010) and this may explain the SeUPE being higher in oilseed rape than in wheat in the present study.…”