heavy metals a few points

Fri Dec 11 17:14:04 EST 1992

Well I am pleased with the response to my plea for discussion on the topic
of heavy metals and plants.
The discussion on hyperaccumulators is interesting but it is important to
realise that to my knowledge there is no example of a plant which excludes
metals, all plants appear to accumulate metals to some degree. This is probably
due to the cationic metal being driven across the PM via the membrame potential
-ve inside. In tobacco this metal then appears to be compartmentalised within
the vacuole. Once inside the vacuole Cd is bound to the induced peptide
phytochelatins, therebye reducing the Cd's chemical gradient across the
tonoplast and hence reducing the amount of energy required to keep pumping
Cd inside. In oats Cd is transported across the tonoplast via a Cd/H
antiport (presumably driven in vivo by tghe tonoplast H-ATPase or H-PPiase).
Transport of Cd back out across the PM may also be a possibility.
RE Datura: P. Jackson at Los Alamos has done alot of work on the
biochemistry of Cd resistence on Datura innoxia in tissue culture!

a recent article in Nature suggests not!(344, 658-660, 1990)
It would appear that Cd can substitute for Zn in Zn deficient marine diatoms!
Does this explain the slight growth stimulation physiologist have seen (but
not talked about) in Cd tolerence tests using root elongation?
What is Cd doing in the marine diatom? Is it siting in the active site of
catalase or in Zn-fingers?....Any ideas.

Finally are there any biophysicists out there how can explain to me why
crystaline CdS is an interesting semiconductor because the fission yeast
S. pombe makes particles of it when exposed to Cd (and may be also plants)
and AT&T Bell laboratories are interested (Nature 338, 596-597, 1989).

David Salt
Botsalt at vm.uoguelph.ca

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