Translocation of Cd and Zn from roots to shoots in different populations of the hyperaccumulator Thlaspi caerulescens

摘要

We investigated variation in the root to shoot transiocation of Cd and Zn and apoplastic bypass flow among ten populations of Thlaspi caerulescens and one population of Thlaspi praecox, using the short-term <'109>Cd and <'65>Zn labelling technique. Additionally. Cd compartmentation in roots in two contrasting ecotypes was quantified from the kinetics of <'109>Cd efflux. On the basis of root fresh weight, total uptake of <'109>Cd and <'65>Zn varied by 5.0 and 6.7 fold, respectively, among the populations studied. The amounts of <109>Cd and <'65> Zn in shoots as a percentage of their total uptake, as an indicator of the translocation efficiency, varied by 4.9 and 4.4-fold, respectively. Apoplastic bypass flow was quantified by a membrane impermeable fluorescent dye. ResuIts showed that the variation in the root to shoot translocation of Cd and Zn among Thlaspi populations was unrelated tO the variation in the root uptake or apoplastic bypass flow.<'109>Cd compartmental analysis indicated that a smaller fraction of the absorbed Cd was stored in the vacuole in the Prayon ecotype (high translocation efficiency), compared with the Ganges ecotype (low translocation efficiency), suggesting that vacuolar sequestration in root cells may be one of the reasons for the variation in the translocation efficiency from roots to shoots in Thlaspi caerulescens.