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

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

herbivory. The insects fed non nickel bearing leaves survived or

hyperaccumulating plant found in the British Isles. It has been

These results demonstrate that zinc hyperaccumulation in

Our results were consistent with other studies in this area.

beaker containing 25ml of solution. The ten Rorison's plants

After twenty days, each plant was transferred to an individual

Several studies have supported the chemical defence

against insect herbivores in two different feeding experiments.

that it is reasonable to assume that the hyperaccumulated metals,

showed weight gain while the insects fed nickel bearing leaves did

investigation, the results were not biased.

Boyd et at (1994) also demonstrated that nickel hyperaccumulating

Some common words found in the essay are:
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Approximate Word count = 1199
Approximate Pages = 5 (250 words per page double spaced)