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Jasmonic acid (JA) is thought to be involved in plant responses to cadmium (Cd) stress, but the underlying molecular mechanisms are poorly understood. Here, we show that Cd treatment rapidly induces the expression of genes promoting endogenous JA synthesis, and subsequently increases the JA concentration in Arabidopsis roots. Furthermore, exogenous methyl jasmonate (MeJA) alleviates Cd-generated chlorosis of new leaves by decreasing the Cd concentration in root cell sap and shoot, and decreasing the expression of the AtIRT1, AtHMA2 and AtHMA4 genes promoting Cd uptake and long-distance translocation, respectively. In contrast, mutation of a key JA synthesis gene, AtAOS, greatly enhances the expression of AtIRT1, AtHMA2 and AtHMA4, increases Cd concentration in both roots and shoots, and confers increased sensitivity to Cd. Exogenous MeJA recovers the enhanced Cd-sensitivity of the ataos mutant, but not of atcoi1, a JA receptor mutant. In addition, exogenous MeJA reduces NO levels in Cd-stressed Arabidopsis root tips. Taken together, our results suggest that Cd-induced JA acts via the JA signaling pathway and its effects on NO levels to positively restrict Cd accumulation and alleviates Cd toxicity in Arabidopsis via suppression of the expression of genes promoting Cd uptake and long-distance translocation., (© 2019 Institute of Botany, Chinese Academy of Sciences.)

Auxin is involved in not only plant physiological and developmental processes but also plant responses to abiotic stresses. In this study, cadmium (Cd(2+)) stress decreased the endogenous auxin level, whereas exogenous auxin (α-naphthaleneacetic acid, NAA, a permeable auxin analog) reduced shoot Cd(2+) concentration and rescued Cd(2+)-induced chlorosis in Arabidopsis thaliana. Under Cd(2+) stress conditions, NAA increased Cd(2+) retention in the roots and most Cd(2+) in the roots was fixed in hemicellulose 1 of the cell wall. NAA treatment did not affect pectin content and its binding capacity for Cd(2+), whereas it significantly increased the content of hemicellulose 1 and the amount of Cd(2+) retained in it. There were highly significant correlations between Cd(2+) concentrations in the root, cell wall and hemicellulose 1 when the plants were subjected to Cd(2+) or NAA+Cd(2+) treatment for 1 to 7d, suggesting that the increase in hemicellulose 1 contributes greatly to the fixation of Cd(2+) in the cell wall. Taken together, these results demonstrate that auxin-induced alleviation of Cd(2+) toxicity in Arabidopsis is mediated through increasing hemicellulose 1 content and Cd(2+) fixation in the root, thus reducing the translocation of Cd(2+) from roots to shoots., (Copyright © 2013 Elsevier B.V. All rights reserved.)

Gibberellic acid (GA) is involved in not only plant growth and development but also plant responses to abiotic stresses. Here it was found that treating the plants with GA concentrations from 0.1 to 5 μM for 24 h had no obvious effect on root elongation in the absence of cadmium (Cd), whereas in the presence of Cd2+, GA at 5 μM improved root growth, reduced Cd content and lipid peroxidation in the roots, indicating that GA can partially alleviate Cd toxicity. Cd2+ increased nitric oxide (NO) accumulation in the roots, but GA remarkably reduced it, and suppressed the up-regulation of the expression of IRT1. In contrary, the beneficial effect of GA on alleviating Cd toxicity was not observed in an IRT1 knock-out mutant irt1, suggesting the involvement of IRT1 in Cd2+ absorption. Furthermore, the GA-induced reduction of NO and Cd content can also be partially reversed by the application of a NO donor (S-nitrosoglutathione [GSNO]). Taken all these together, the results showed that GA-alleviated Cd toxicity is mediated through the reduction of the Cd-dependent NO accumulation and expression of Cd2+ uptake related gene-IRT1 in Arabidopsis., (Copyright © 2012 Elsevier B.V. All rights reserved.)

The physiological and molecular mechanisms leading to the competitive interactions between phosphorus (P) and metal elements are a matter of debate. In this study, we found that P deficiency can alleviate cadmium (Cd) toxicity in Arabidopsis thaliana (Col-0). Under P deficiency (-P), less Cd was accumulated in the plants and the root cell walls, indicating the operation of a P-deficiency-induced Cd exclusion mechanism. However, organic acid efflux was similar under -P+Cd and +Cd treatments, suggesting that organic acid efflux is not responsible for the Cd exclusion. Interestingly, P deficiency significantly decreased cell wall polysaccharides (pectin and hemicellulose) contents and pectin methylesterase activity, and decreased the Cd retained by the extracted root cell wall. Therefore, we conclude that the modification of cell wall composition is responsible for the Cd exclusion of the root under P deficiency.

Summary: Rice grain is a poor dietary source of zinc (Zn) but the primary source of cadmium (Cd) for humans; however, the molecular mechanisms for their accumulation in rice grain remain incompletely understood.This study functionally characterized a tonoplast‐localized transporter, OsMTP1. OsMTP1 was preferentially expressed in the roots, aleurone layer, and embryo of seeds. OsMTP1 knockout decreased Zn concentration in the root cell sap, roots, aleurone layer and embryo, and subsequently increased Zn concentration in shoots and polished rice (endosperm) without yield penalty. OsMTP1 haplotype analysis revealed elite alleles associated with increased Zn level in polished rice, mostly because of the decreased OsMTP1 transcripts.OsMTP1 expression in yeast enhanced Zn tolerance but did not affect that of Cd. While OsMTP1 knockout resulted in decreased uptake, translocation and accumulation of Cd in plant and rice grain, which could be attributed to the indirect effects of altered Zn accumulation.Our results suggest that rice OsMTP1 primarily functions as a tonoplast‐localized transporter for sequestrating Zn into vacuole. OsMTP1 knockout elevated Zn concentration but prevented Cd deposition in polished rice without yield penalty. Thus, OsMTP1 is a candidate gene for enhancing Zn level and reducing Cd level in rice grains. [ABSTRACT FROM AUTHOR]