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Zinc Hyperaccumulation

  • Date Submitted: 01/28/2010 06:29 AM
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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



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...


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