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Re: Iron, chelates, and pathways

Steve Pushak wrote

> Oops! I said in the last message that ONLY Fe2+ is
> absorbed into the plant root or leaf. That's not quite
> accurate. There is another mechanism called Strategy
> 2 which involves phytosiderophores. I've taken the
> liberty of quoting the description:
>    "Strategy 2 - Monocotyledonous plants (grasses)
>    This uses Fe complexing compounds called phytosiderophores
>    to mobilize Fe in the rhizosphere (see the summary diagram
>    below). The phytosiderophores (negatively charged amino
>    acids) are released by a specific transporter (an anion antiport ?)
>    into the soil. They then diffuse towards Fe(OH)3+ where they
>    complex Fe. They can then diffuse back to the root where the
>   whole complex is taken back up into the root (by a H+-symporter).
>   The Fe3+ is not reduced to Fe2+ and the chelator does not
>   return directly back to the soil (as in Strategy 1 plants). In the
>   soil the phytosiderophores can become sorbed to the anion
>   exchange phase (as they are strongly negatively charged) or
>   they can be ingested and decomposed by the soil's microbial
>   biomass. "

I probably take this stuff up more slowly than the plants but lets keep
the discussion going anyway!

Greg Morin has indicated that the commercial chelators typically use
Fe+++.   And I have read this is the typical form in nature.  Additionally,
it is commonly accepted that Fe++ is the bioavailable form but that it
doesn't last very long ( at the typical oxygen levels found ) in our
aquaria.

What is the foliar mechanism for obtaining bioavailable Fe++ ? ( how
do  algae, rootless plants and the stems and leaves of rooted plants )  get
bioavailable Fe++ ?  It seems to me  the following are possible:

   1)   Free Fe++ is extracted from the water column for the
         very brief time it is available. ( before being oxidised to Fe+++
         or combining with orthophosphate )
   2)  The entire chelate complex is taken up and further processed
        to obtain Fe++.
   3)  Fe+++ is more bioavailable than is typically written

Of course it is possible that algae and rootless plants have a mechanism
apart from rooted plants and that rooted plants use some combination of
the above.

Christopher Coleman
christopher.coleman at worldnet_att.net