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Iron utilization by plants

Date: Sun, 25 Feb 2001 18:08:58 -0500 (EST)
From: Shawn Prescott <fishvet at shado_jaguNET.com>
Subject: Iron Test Kits


I would like to make an addition to the statements below, as they may cause
undue concern to fellow hobbyists:

:All plants whether terrestial or aquatic can ONLY utilize Ferrous iron,
:cannot assimilate Ferric. Thus using a test kit no matter whether it
:develops slowly or quickly that does not measure Ferrous iron, will only
:cause the Hobbyist to be misled.

:Shawn Prescott .

:Fish-Vet Inc.	

There are many species of plants that utilize ferric iron directly.  These
are the graminaceous species (grasses).  They secrete compounds known a
phytosiderophores from the roots.  The siderophores chelate ferric iron,
then the entire siderophore-iron complex is taken into the root, and the
ferric iron is released.  You are correct that most plants use only ferrous
iron for uptake, however, this does NOT mean that ferric iron cannot be
utilized by plants.  Prior to uptake, the ferric iron is reduced to ferrous
iron by an enzyme (ferric reductase).  Therefore, knowing the total iron,
ferric plus ferrous, IS a valid measurement.  I'm not sure how the hobby
test kits work chemically, but assuming it works like ferric reductase
assays, there is a ferrous scavenger that forms a red or purple color when
bound with ferrous iron.  If this is the case, then the long time period
required for color development could be sped up by adding some ascorbate
(vitamin C) solution. (i.e. crush and dissovle a vitamin tablet in as little
water as possible and add a drop or two.  Make fresh each time.)

Brian Waters