Re: Scientists testing plants in fight against radioactivity

["Björn Cedervall" <bjorn_cedervall@hotmail.com>]

As an interested amateur, I wrote a review on taxonomic
aspects of "heavy" metal uptake in angiosperms around 1981.
It was supposed to be a limited study (like three months'
work) but quickly swelled and I had to put an end to the
writing after about 100 pages (in English).
The report was a type of internal work related to the
biochem. dept. at the Royal Inst. Technology in Stockholm.
If somebody is particularly interested, I can fax the
reference list (about 140 refs. I think) - I can come
back and give a few particularly illuminating refs. here
later. Two major mechanisms regarding metal _tolerance_ were:
1. Ability to exclude the metal in question when present
in high concentration in soil.
2. A tolerance for a high tissue concentration of the
metal (Examples B(l?)echium homblei (Copper) and Haumaniastrum sp. 
(Cobalt), both of the Lamiaceae family). These types of mechanisms gave 
the species a competitive advantage as compared to other species.
Some grass species were amazingly rapid with their adaption to toxic
metal heaps/dumps - I interpreted this as the "tolerance genes"
(whatever they were) already existed as low frequency alleles
in the population - rather than that they were created through
new mutations. All this was very complex and I was left with
a lot of guess work. There are many plants that specifically
tolerate or take up various more odd metals such as silver,
uranium and others. Unfortunately, some of the above mentioned
types of species are threatened by extinction since their presence
indicate where to mine for the metals. The two members of the
Lamiaceae family (above) occur in the Zimbabwe region in Africa.
Actually there were whole "toxic metal" (Cr, Co, Cu) specific
plant communities there (300-400 different species if I remember right) 
indicating the metals (good for archaeology research also).
I included the floras of the Scandinavia, Pacific NW, California
and S. Korea/Japan (limited info.) (with some emphasis on
serpentine plants). For PNW and Calif. (6000 species) I checked
every single species of the Munz flora. One conclusion from
this was that although there sometimes were, not surprisingly, 
"taxonomic clusters" (closely related species) showing tolerance
to the same "toxic metal" - there were no simple taxonomic rules.
In Scandinavia, some of the more interesting species tolerating
serpentine soil belong to the Caryophyllaceae (don't know the
English name - beautiful flowers - usually white-pink-red) and
Poaceae (grasses) families (I think there were some Cyperaceae
(sedge?) specieas also. This did not seem reflected by the flora
of Calif. for instance.

Bjorn
bjorn_cedervall@hotmail.com
Depts. Medical Radiation Biology and Medical Radiation Physics,
Karolinska Institutet, Box 260,
S-171 76 Stockholm, Sweden
Ph/fax: Int + 468 343525 (Med. Radiation Physics)
Personal website:
http://www.geocities.com/WallStreet/Exchange/8256/


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