Cadmium adsorption in leaf cell walls prevents redistribution to silique in Arabidopsis thaliana ecotypes Jm-1 and Kyo-0

Cadmium (Cd) redistribution from leaf to silique determined seed Cd content in Arabidopsis, but the control mechanism remains largely unknown. Here, we found that the Cd concentrations in the leaves, stems, and siliques of Arabidopsis thaliana (A. thaliana) ecotype Jm-1 were higher than in the ecotype Kyo-0. The Cd concentrations in the leaves’ cell walls (CW) were 39% lower in Jm-1 than in Kyo-0, while the concentrations in the CW of the stem and silique were 14% and 42% higher in Jm-1. The Cyclohexane Diamine Tetraacetic Acid (CDTA)-pectin and hemicellulose in Kyo-0 had higher Cd concentrations than those of Jm-1. The pectin methylesterase (PME) activity was 19% higher in Kyo-0 than in Jm-1, and the expression levels of PME1, PME2, PME12, and PME25 were upregulated in Kyo-0 after Cd treatment. In addition, the Cd and Fe concentrations in the phloem was 36% and 73% higher in Jm-1 than in Kyo-0 respectively. The expression of iron transport-related genes showed that only YSL3 and ZIP11 had significant differences between the two ecotypes after Cd treatment. Kyo-0 accumulated less Cd than Jm-1 in the silique, which may be because (1) the activity of PME that is mainly regulated by PME1, PME2, PME12, and PME25 was higher in Kyo-0 leaves, leading to more Cd chelation in the pectin of the CWs, and (2) the expression of YSL3 was 2 times lower in Kyo-0 leaves， which regulate the transport of Cd in the phloem, thus reducing the transport of Cd to the silique.