Subject: poisonous plants--nickel hyperaccumulators

From: [email-masked] (Scott Martens)
Date: 7 Aug 1995 21:49:53 GMT

There are relatively few plants that accumulate sufficient levels of
elements from soil to render themselves acutely toxic to herbivores. 
Nickel "hyperaccumulators", capable of accumulating more than 1000 ppm Ni,
however, can do so.  There are only about 200 or so nickel
hyperaccumulating species known, but they occur nearly everywhere Ni-rich,
serpentine-derived soils occur around the world.  We (Martens and Boyd,
1994) have shown that a Californian nickel-hyperaccumulator, Streptanthus
polygaloides (Brassicaceae), is acutely toxic to potential herbivores
(lepidopteran larvae, as well as grasshoppers), and demonstrated similar 
results for Thlaspi montanum (Brassicaceae) (Boyd and Martens, 1994).  We 
have also been able to show that fungal and bacterial pathogens are 
deterred by nickel hyperaccumulation (Boyd et al., 1994).  Large, mobile 
herbivores might circumvent the nickel defense simply by consuming a 
mixed diet, but many bacterial and fungal pathogens, and insect 
herbivores, spend all (or nearly all) of their lives on a single host 
plant.  Nickel hyperaccumulation seems to be an effective defense because 
of its high lethality, apparent low cost to the plant, and broad spectrum 
of toxicity.  For more info you might check out the papers below:

Martens, Scott N. and Robert S. Boyd. 1994.  The ecological significance 
of nickel hyperaccumulation:  a plant chemical defense.  Oecologia 
98:379-384.

Boyd, Robert S. and Scott N. Martens. 1994.  Nickel hyperaccumulated by 
Thlaspi montanum var. montanum is acutely toxic to an insect herbivore.  
Oikos 70:21-25.

Boyd, Robert S., Joe J. Shaw, and Scott N. Martens. 1994.  Nickel 
hyperaccumulation defends Streptanthus polygaloides (Brassicaceae) 
against pathogens.  American Journal of Botany 81:294-300.

Scott N. Martens
Department of Land, Air, and Water Resources
University of California, Davis
Davis, CA  95616

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