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
ABSTRACT
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...
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