title: The apoplasmic pathway via the root apex and lateral roots contributes to Cd hyperaccumulation in the hyperaccumulator Sedum alfredii.
abstract: Although the significance of apoplasmic barriers in roots with regards to the uptake of toxic elements is generally known, the contribution of apoplasmic bypasses (ABs) to cadmium (Cd) hyperaccumulation is little understood. Here, we employed a combination of stable isotopic tracer techniques, an ABs tracer, hydraulic measurements, suberin lamellae staining, metabolic inhibitors, and antitranspirants to investigate and quantify the impact of the ABs on translocation of Cd to the xylem in roots of a hyperaccumulating (H) ecotype and a non-hyperaccumulating (NH) ecotype of Sedum alfredii. In the H ecotype, the Cd content in the xylem sap was proportional to hydrostatic pressure, which was attributed to pressure-driven flow via the ABs. The contribution of the ABs to Cd transportation to the xylem was dependent on the Cd concentration applied to the H ecotype (up to 37% at the highest concentration used). Cd-treated H ecotype roots showed significantly higher hydraulic conductance compared with the NH ecotype (76 vs 52 × 10–8 m s–1MPa–1), which is in accordance with less extensive suberization due to reduced expression of suberin-related genes. The main entry sites of apoplasmically transported Cd were localized in the root apexes and lateral roots of the H ecotype, where suberin lamellae were not well developed. These findings highlight the significance of the apoplasmic bypass in Cd hyperaccumulation in hyperaccumulating ecotypes of S. alfredii.
authors.affiliation: Ministry of Education Key Laboratory of Environmental Remediation and Ecological Health, College of Environmental and Resource Sciences, Zhejiang University, Hangzhou, China.|Department of Plant Physiology, Faculty of Natural Sciences, Comenius University in Bratislava, Mlynska dolina,  Bratislava, Slovakia.
authors.forename: Qi
authors.initials: Q
authors.lastname: Tao
authors.affiliation: Department of Experimental Biology, Faculty of Science, Masaryk University, Kotlarska, Brno, Czech Republic.
authors.forename: Radek
authors.initials: R
authors.lastname: Jupa
authors.affiliation: Ministry of Education Key Laboratory of Environmental Remediation and Ecological Health, College of Environmental and Resource Sciences, Zhejiang University, Hangzhou, China.
authors.forename: Jipeng
authors.initials: J
authors.lastname: Luo
authors.affiliation: Department of Plant Physiology, Faculty of Natural Sciences, Comenius University in Bratislava, Mlynska dolina,  Bratislava, Slovakia.
authors.forename: Alexander
authors.initials: A
authors.lastname: Lux
authors.affiliation: Department of Plant Physiology, Faculty of Natural Sciences, Comenius University in Bratislava, Mlynska dolina,  Bratislava, Slovakia.
authors.forename: Ján
authors.initials: J
authors.lastname: Kováč
authors.affiliation: Ministry of Education Key Laboratory of Environmental Remediation and Ecological Health, College of Environmental and Resource Sciences, Zhejiang University, Hangzhou, China.
authors.forename: Yue
authors.initials: Y
authors.lastname: Wen
authors.affiliation: Ministry of Education Key Laboratory of Environmental Remediation and Ecological Health, College of Environmental and Resource Sciences, Zhejiang University, Hangzhou, China.
authors.forename: Yimei
authors.initials: Y
authors.lastname: Zhou
authors.affiliation: Ministry of Education Key Laboratory of Environmental Remediation and Ecological Health, College of Environmental and Resource Sciences, Zhejiang University, Hangzhou, China.
authors.forename: Japenga
authors.initials: J
authors.lastname: Jan
authors.affiliation: Ministry of Education Key Laboratory of Environmental Remediation and Ecological Health, College of Environmental and Resource Sciences, Zhejiang University, Hangzhou, China.
authors.forename: Yongchao
authors.initials: Y
authors.lastname: Liang
authors.affiliation: Ministry of Education Key Laboratory of Environmental Remediation and Ecological Health, College of Environmental and Resource Sciences, Zhejiang University, Hangzhou, China.
authors.forename: Tingqiang
authors.initials: T
authors.lastname: Li
mesh_terms: D002104:Cadmium / Q000378:metabolism*; D060146:Ecotype; D015870:Gene Expression; D008055:Lipids / Q000235:genetics / Q000502:physiology*; D018517:Plant Roots / Q000378:metabolism*; D031963:Sedum / Q000235:genetics / Q000378:metabolism*; D052584:Xylem / Q000378:metabolism*
chemical_list: D008055:Lipids; D002104:Cadmium; C065875:suberin
keywords: Apoplasmic bypass; cadmium; hydraulic conductance; lateral roots; root apex; Sedum alfredii; suberin lamellae; trisodium-8-hydroxy-1,3,6-pyrenetrisulphonic acid (PTS)