Kevin's example #1:
>1) Heavy metal toxicity resistance in plants. Before the modern
>industrial age there simply wasn't enough lead, cadmium or mercury around
>for plants to worry about. Now there are places in the world where the
>soil is so contaminated with these and other heavy metals that plants can
>die unless protected.
This is a common misconception today - the idea that before man or
before the modern industrial age there weren't any problems with heavy
metal toxicity. In fact, this has always been a problem. Our modern
society has only exacerbated the problem by increasing the number of
"contaminated" sites. All of these metals come from naturally
occurring ore deposits which, when eroded and exposed at the earth's
surface, created "natural contamination" (an oxymoron term used to
emphasis my point.) Even before our modern industrial age, plant
communities had to deal with heavy metal toxicity. Pre-industrial age
animal and human populations also had to deal with areas of naturally
poisoned soils. (And our theology must be able to deal with a world
created with areas that were naturally toxic to human life.)
In the field of exploration geochemistry, plants have been used to
prospect for these areas of "natural contamination" in hopes that
enough of the metals remain to be mined. There are two related fields
of research -- biogeochemistry and geobotany -- that have been pursued
for these purposes (and for environmental purposes). In
biogeochemistry, plants are sampled and analyzed to determine their
heavy metal content - plants from areas of "natural contamination"
normally contain elevated concentrations of interesting elements.
Geobotany deals with the recognition of "indicator plants" - plants
that are tolerant or thrive on specific and often toxic soils. This
relationship between plants and ore deposits was mentioned in the
writings of Vitruvius, the 1st century B.C. Roman architect and
engineer and even more specifically by the 16th century German mining
engineer Agricola.
>Those that can survive had mutations that created
>proteins that were able to bind up these heavy metals and sequester them
>away from other proteins and the DNA.
I have no problems with this statement since mechanisms for toxicity
resistence arose in these plants at some time in the past and
experiments have shown similar results on other species today.
>This function never existed before,
>could never exist before, because only recently have plants started
>encountering these kinds of metals.
Actually this function has arisen several times and acts in different
fashions in different plants. Some plants accumulate the toxic metals
in leaves which are then shed. Many grasses tolerate "contaminated"
soils by preventing the element from concentrating in the aerial parts
of the plant, either by storing the metals in the root system or by
mechanisms which filter out harmful metals (Cannon, 1979). Some
plants actually evolve a dependence upon the toxic metal and use that
element in their own "defense" from menacing herbivores (i.e. loco
weed).
Since this subject is of economic interest, there are several papers
in the journals. I have several references and will only include a
few here for those who may be interested.
Canney, F.C., Cannon, H.L., Cathrall, J.B., and Robinson, K., 1979,
Autumn colors, insects, plant disease, and prospecting: Economic
Geology, v. 74, p. 1673-1676.
Cannon, H.L., 1979, Advances in botanical methods of prospecting for
metals. Part I - Advances in geobotanical methods, _in_ Hood,
P.J., ed., Geophysics and Geochemistry in the Search for Metallic
Ores: Geological Survey of Canada, Economic Geology Report 31, p.
385-395.
Smith, R.A. and Bradshaw, A.D., 1970, Reclamation of toxic
metalliferous wastes using tolerant populations of grass: Nature,
v. 227, no. 5256, p. 376-377.
Steve
[The opinions expressed here are my own
and are not to be attributed to my employer.]
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