Zinc hyperaccumulation in Thlaspi caerulescens.
as a chemical defence against herbivory.
Thlaspi caerulescens is one of several plant species known to.
accumulate heavy metals in excess of 2% of their above ground plant.
biomass. The reasons for hyperaccumulation are unknown, but.
several studies conclude that it may be a plant chemical defence.
This has been of interest to biologists because these metals are.
usually toxic. The accumulation of these metals may serve as a.
model for coevolution. We examined the effects of zinc.
hyperaccumulation in Thlaspi on Xanthomonas campestris and found.
that the plants containing zinc thrived when inoculated with this.
bacteria, while plants not containing zinc showed signs of.
deterioration.
INTRODUCTION.
There are several wild plant species that have the ability to.
accumulate high quantities of heavy metals in their above ground.
biomass, up to three percent or more. Many of these plants are.
found in the Brassicaceae family throughout Europe and the British.
Isles. These plants thrive on mineral outcrops with calamine and.
serpentine soils rich with high levels of zinc, cadmium, and nickel.
(Baker et al, 1994). Several theories have been advanced on the.
reasons for this hyperaccumulation. Boyd and Martens propose that.
it could be a form of drought resistance, inadvertent uptake,.
interference, tolerance or disposal of metal from the plant, or a.
chemical defence against herbivory or pathogens.
Several studies have supported the chemical defence.
hypothesis. Martens and Boyd (1994 and Boyd and Martens, 1994) .
showed that nickel hyperaccumulation is an effective defence.
against insect herbivores in two different feeding experiments. .
Boyd et at (1994) also demonstrated that nickel hyperaccumulating.
plants resisted pathogens including Xanthomonas campestris.
Thlaspi caerulescens J. and C. Presl (Brassicaceae) is a.
hyperaccumulating plant found in the British Isles. It has been.
shown to accumulate 10,000 ppm (>1%) of its biomass in zinc (Baker.
