heavy metals a few points

[Tony Travis]

In article <921211224901.MIN-LHFCa00330.bionet-news at uk.ac.daresbury> you wrote:
: [...]
: 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
: [...]

I did some work with benzo-18-crown-6 (a synthetic ionophore) which
demonstrated that accumulation of K+ in the vacuole of stomatal guard
cells was dependent on the permeability of the PM to K+ ions.  The
crown ether is incorporated into the membrane and forms K+ permeable
channels.

The driving force for accumulation of K+ is electrogenic proton
extrusion across the PM/tonoplast.  It seems that accumulation of Cd or
any other cation available would depend on membrane permeability rather
than active transport of the metal itself.

	Tony.
--
Dr. A.J.Travis,                       |  Tony Travis
Rowett Research Institute,            |  JANET: <ajt at uk.ac.sari.rri>
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