The apoplasmic pathway via the root apex and lateral roots contributes to Cd hyperaccumulation in the hyperaccumulatorSedum alfredii

Abstract

HighlightA portion of the cadmium taken up by the hyperaccumulator Sedum alfredii can be apoplasmically transported to the xylem via root apexes and lateral roots, where the suberin lamellae are not well developed.

Abscisic acid‐mediated modifications of radial apoplastic transport pathway play a key role in cadmium uptake in hyperaccumulator Sedum alfredii

“…Most of early literatures pointed out that transporter‐mediated symplastic and coupled transcellular pathways were the only pathways for Cd influx (Lu et al, ; Van der Vliet, Peterson, & Hale, ; Zhao, Hamon, Lombi, McLaughlin, & McGrath, ) whereas the apoplastic pathway was associated with low importance for radial transport of Cd. Nevertheless, our recent study demonstrated that up to 37% of all Cd ions could directly move to the xylem of a hyperaccumulating ecotype of Sedum alfredii via the apoplastic pathway, and relative proportions of Cd taken up through apoplastic pathway were substantially higher in the hyperaccumulating than in the nonhyperaccumulating ecotype (Tao et al, ). However, the physiological and molecular mechanisms leading to the large intraspecific differences in contribution of apoplastic pathway to Cd uptake are not clear.…”

“…Cd‐hyperaccumulators, plants possessing the ability to tolerate and accumulate high concentrations of Cd, are of great potential for phytoremediation of Cd‐contaminated soils (Krämer, ; Zhao, Jiang, Dunham, & McGrath, ). To date, several processes determining the efficiency of Cd hyperaccumulation have been documented, including increased mobilization of Cd in rhizosphere (Li et al, ), facilitated radial transport in roots (Tao et al, ), enhanced long‐distance transport in xylem (Lu et al, ), and effective sequestration and detoxification in shoot (Tian et al, ). From those processes, radial transport in roots is crucial to the accumulation of Cd in the aboveground organs, because it determines the amount of Cd ions moving from epidermis to stele (Belimov et al, ; Lux, Martinka, Vaculík, & White, ; Tao et al, ).…”

“…During ontogenetic development of a root, the endodermal cells form specific barriers, the Casparian strips (CSs) and the suberin lamellae (SL), which play a crucial role in impeding transport of water and dissolved ions via apoplastic pathway (Barberon, ; Tao et al, ). Therefore, opportunity for the apoplastic bypass increases with the root proportions containing no apoplastic barriers, typically in the root apical region (Barberon et al, ; Geldner, ).…”

“…Therefore, opportunity for the apoplastic bypass increases with the root proportions containing no apoplastic barriers, typically in the root apical region (Barberon et al, ; Geldner, ). In addition, free apoplastic penetration of dissolved Cd ions is also possible along lateral roots where CSs have been disrupted during root emerging (Li et al, ; Tao et al, ). As many previous studies showed (Martinka & Lux, ; Schreiber, Hartmann, Skrabs, & Zeier, ; Vaculík, Lux, Luxová, Tanimoto, & Lichtscheidl, ), both chemical composition and deposition of CSs/SL in roots are sensitively regulated by various types of abiotic stresses.…”

“…S. alfredii (Crassulaceae) is a Zn/Cd hyperaccumulator with significant potential for utilization in phytoremediation (Yang & Stoffella, ). Previous experiments using hyperaccumulating (HE) and nonhyperaccumulating ecotype (NHE) have elucidated the significant contribution of apoplastic pathway to total Cd uptake and transport in this species (Tao et al, ). However, specific mechanisms modulating the apoplastic pathway in the context of ABA are still vacant in S. alfredii .…”