Cadmium adsorption, chelation and compartmentalization limit root-to-shoot translocation of cadmium in rice (Oryza sativa L.)

Abstract

Strategies to reduce cadmium (Cd) in rice grain, below concentrations that represent serious human health concerns, require that the mechanisms of Cd distribution and accumulation within rice plants be established. Here, a comprehensive hydroponic experiment was performed to investigate the differences in the Cd uptake, chelation and compartmentalization between high (D83B) and low (D62B) Cd-accumulation cultivars contrasting in Cd accumulation in order to establish the roles of these processes in limiting Cd translocation from root to shoot. D83B showed 3-fold higher Cd accumulation in the shoots than the cultivar D62B. However, a short-term Cd uptake experiment showed more Cd uptake by D62B than by D83B. The distribution of Cd in roots and shoots differed significantly. D83B translocated 38% of total Cd taken up to the shoots, whereas D62B retained most of the Cd in the roots. D62B had higher amounts of non-protein thiols (NPTs) and glutathione (GSH) than D83B. The NPT and Cd distribution ratio (CDR) in the anionic form in the roots of D62B increased gradually as Cd concentration increased. In D83B, in contrast, levels of CDR in the cationic form increased significantly from 22.10 to 43.37%, while NPT only increased slightly. Furthermore, the percentage of Cd ions retained in thiol-rich peptides, especially in the HMW complexes, was significantly higher in D62B compared with D83B. However, D83B possessed a greater proportion of potentially mobile (cationic) Cd in the roots and showed superior Cd translocation from root to shoot. Taken as a whole, the results presented in this study revealed that Cd chelation, compartmentalization and adsorption contribute to the Cd retention in roots.

Cadmium isotope fractionation in the soil – cacao systems of Ecuador: a pilot field study

“…This tentative inference is in accord with previous elemental studies, which revealed signicant differences in the partitioning of Cd between plant organs for different cultivars of cacao, 7,30 and other crops. [26][27][28][29] Also notable is that the enrichment of light Cd isotopes in beans of the relatively pure Nacional cultivar (Tables 2 and 3) is in accord with observations made for Cd-tolerant and Cd accumulator plants, as these also revealed an enrichment of light Cd isotopes in stems and leaves relative to the hydroponic solution in which they were cultured. 62 The latter observation was thereby linked to the particular molecular mechanisms employed by these plants to cope with high levels of toxic Cd.…”

“…25 Previous studies on annual crops such as barley, potatoes and rice revealed clear cultivar-specic differences in Cd uptake and particularly root to shoot translocation, whereby the latter appears to be governed by the ability of plants to sequester Cd in roots with the aid of transporter proteins. [26][27][28][29] Two recent investigations on cacao also revealed cultivar-specic differences in Cd handling but with contrasting results. One study found that cultivars primarily differ in the efficiency of Cd translocation from shoots to beans, due to differences in the efficiency of Cd transfer from xylem to phloem.…”

Alleviating the Cadmium Toxicity and Growth‐Promotion in Paddy Rice by Photosynthetic Bacteria

“…However, the composite bacteria including B. subtilis and RP obviously reduced the concentration of Cd in rice grains. Presumably, B. subtilis partly formed spores for dormancy, while others rapidly consumed free oxygen in the soil environment, leading to local hypoxia . Paddy soil showed relatively anaerobic conditions when soaked with water .…”

Identification of Cd Accumulation and Translocation Ability for the Root of 20 Rice Cultivars

“…Our study held that the accumulation amount of Cd and NPT were significantly positively correlated. The previous studies have shown that the GSH content in root for low-Cd rice varieties is higher than that for high-Cd rice cultivars [24]. Phytochelatin (PC), as a kind of NPT, plays an important role in the metastasis ability of Cd in rice cells.…”