Arabidopsis halleri subsp. gemmifera, a close wild relative of A. thaliana in eastern Asia, is an important model species of Brassicaceae used to study cadmium (Cd) and zinc (Zn) tolerance and hyperaccumulation in plants. To investigate the effects of soil factors on metal accumulation in this plant, we collected plants and rhizosphere soil samples from a limestone mining site on Mount Ibuki, and compared them with those collected from non-calcareous soil in Japan. Irrespective of the sampling site, all the plants efficiently accumulated Cd in shoot tissues. The plants growing on non-calcareous soil also accumulated Zn in shoot tissues, but shoot Zn concentration in plants growing on calcareous soils was below the level required for hyperaccumulators. The pH of calcareous soil samples was between 7.68 and 8.21. Total Zn contents were similar in calcareous and non-calcareous soils, but the amounts of Zn extractable by 0.1 M HCl were lower in calcareous than in non-calcareous soil. These results indicate that the properties of calcareous soil affect metal accumulation in plants.
Arabidopsis kamchatica ssp. kawasakiana, a member of the family Brassicaceae, is an endangered winter annual species that grows on sandy coasts and lakesides. A. kamchatica is an allotetraploid plant produced by the hybridization of two closely related diploid taxa, the Zn/Cd hyperaccumulator A. halleri and the non-accumulator A. lyrata. The heavy metal accumulation and vegetation ecology of A. k. ssp. kawasakiana were investigated by collecting leaves and rhizosphere soil samples in three natural habitats on the shore of Lake Biwa in Japan. Leaf Zn contents in almost all plants were above the level required by hyperaccumulators. Plants from one habitat preferred to grow on soils with topical high Zn levels, whereas rhizosphere soils from other populations contained basal levels of Zn suggesting that plant vegetation is more affected by soil disturbance and by soil Zn contents. A. k. ssp. kawasakiana plants were also found to be tolerant to Zn and Cd, in contrast to the nontolerant species A. thaliana. These findings indicated that A. k. ssp. kawasakiana is a facultative Zn hyperaccumulator, inheriting the trait from its parent A. halleri. Furthermore, A. k. ssp. kawasakiana is a self-compatible plant and Arabidopsis floral dip transformation might be applicable to this plant. Considering their natural diversity, A. k. ssp. kawasakiana will help the determination of the molecular mechanisms by which plants accumulate and tolerate heavy metals.
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