Abstract
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.
Highlights
Along with the rapid progress of industrialization and urbanization in the world, soil Cd pollution has become an increasingly serious problem
Kyo-0 accumulated less Cd than Jm-1 in the silique, which may be because (1) the activity of pectin methylesterase (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 cell wall (CW), and (2) the expression of YSL3 was induced to regulate the transport of Cd in the phloem, reducing the transport of Cd to the silique
Demethylation creates a negative charge on pectin polysaccharides, which plays an important role in growth, adsorbing cations, and binding to proteins and homogalacturonic acid (HG) cross-linking complexes (Ca2+-pectate cross-linked complexes, the so called “egg-boxes”) in the CW[14,15]
Summary
Along with the rapid progress of industrialization and urbanization in the world, soil Cd pollution has become an increasingly serious problem. Cadmium accumulation may induce toxic effects in crops, such as by inhibiting normal cell division, reducing photosynthesis efficiency of the blade, increasing membrane lipid peroxidation, and inhibiting the activity of antioxidant enzymes[2,3]. These effects inhibit normal plant growth and reduce yields. Pectin in the CW is one of the main binding sites for cations[11], and there is increasing evidence that CW pectin polysaccharides play a role in the resistance of plants to heavy metals. Hocq[17] postulate that precise and dynamic modulation of extracellular pH plays a central role in the control of HG-modifying enzyme activities and in particular those of pectin methylesterases and polygalacturonases
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