On the contribution of cadmium – citrate complexes to cadmium uptake by durum wheat

• Published in: Plant and soil 2023-06, Vol.487 (1-2), p.455-465
• Main Author: Sterckeman, Thibault
• Format: Article
• Language: English
• Subjects: Agricultural sciences; Agriculture; Agronomy; Analysis; Aqueous solutions; Biomedical and Life Sciences; Cadmium; Citrates; Citric acid; Coordination compounds; Dissociation; Durum wheat; Ecology; Exposure; Genetics; Hydroponics; Influence; Life Sciences; Pasta; Plant Physiology; Plant Sciences; Plants genetics; Research Article; Soil Science & Conservation; Speciation; Transpiration; Triticum durum; Wheat
• ISSN: 0032-079X; 1573-5036
• DOI: 10.1007/s11104-023-05943-6

Purpose To determine if the increase in Cd uptake by durum wheat in the presence of Cd-citrate is due to dissociation or to the transpiration-driven apoplastic uptake of the complex. Methods A mechanistic model of Cd uptake in hydroponics was developed, formalising the transport of Cd, citrate and their complex, including the dissociation of the latter and its uptake through apoplastic pathway. Model outputs were compared to Cd and citrate uptake by durum wheat exposed to 35 and 117 nM Cd 2+ in aqueous solution, in absence and presence of citrate. Results A quasi-doubling (+ 94%) of the Cd uptake was measured when the exposure solution was theoretically 80 nM Cd-citrate in addition to the 35 nM Cd 2+ , when compared to the exposure to 35 nM Cd 2+ alone. The model precisely predicted the Cd uptake with Cd 2+ at the two exposure levels (35 and 117 nM Cd 2+ ) without ligand. In the presence of citrate, the modelling showed that Cd-citrate dissociation could increase the Cd uptake by 18.1%. Including the uptake of Cd-citrate through apoplastic uptake increased the simulated uptake by only 19.6%. The [Cd 2+ ] measured here was twice that calculated using VisualMINTEQ (35 nM). Using the measured values of Cd speciation enabled an accurate prediction of the metal uptake. Conclusions In the presence of citrate, durum wheat principally absorbs free hydrated Cd ions. The dissociation of the Cd-citrate complexes makes a minor contribution to the Cd 2+ uptake flux, while their apoplastic uptake can be regarded as practically negligible.