Accumulation of zinc and cadmium and localization of zinc in Picris divaricata Vant.

Picris divaricata Vant., a plant species native to subtropical China, was recently identified as the first Cd/Zn hyperaccumulator from Asteraceae. P. divaricata was grown from wild collected seed for 4 months in a series of pH adjusted test soils with added Zn levels 0–7000 mg kg−1 and Cd levels 0–150 mg kg−1. Plants did not hyperaccumulate Zn (threshold >3000 μg g−1) and weakly hyperaccumulated Cd with little or no dose–response.P. divaricata has multicellular simple trichomes concentrated on the leaf margins and midrib. X-ray analysis showed that Zn was concentrated in larger trichomes and epidermal cells adjacent to the trichome but virtually absent in other leaf tissues. Within the trichomes, Zn was localized in ovate spots around the tips of individual cells. These tips and other locations in the trichome cell contained black electron dense material when examined with transmission electron microscopy, some of which was identified as SiO2. Silicon and Mn were concentrated in the same areas as Zn. Si has been previously associated with alleviating Zn, Mn and Cd toxicity. Our results support this observation and further investigation is warranted.Calcium and P were concentrated in the distal tips of trichomes, similar to patterns previously observed for calcicole plants grown in elevated Ca soils. Overall, nonsecretory trichomes from many plant families may have a common origin as tissues adapted to handle a variety of environmental metals.

► P. divaricata has Zn localized in larger trichomes and epidermal cells adjacent to the trichome but virtually absent in other tissues.
► Silicon and Mn were concentrated in the same areas as Zn. Si has been previously associated with alleviating Zn, Mn and Cd toxicity.
► Calcium and P were concentrated in the distal tips of trichomes, similar to patterns observed for calcicole plants grown in elevated Ca soils.
► P. divaricata grown in a series of Zn/Cd test soils did not hyperaccumulate Zn and weakly hyperaccumulated Cd.
► Nonsecretory trichomes may have a common origin as tissues adapted to handle a variety of environmental metals.