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Re: Trace Elements and fulvenes

James Purchase wrote:

> Kassebeer goes on to discuss the fact that "bound" micronutrients are not
> absorbable by the plants and that there is some "suspected" method whereby
> the plant makes it's own "complex-formers" which act as the transfer
> mechanism to get the micronutirents into the plant tissue. 

This sounds like phytosiderophores which are used by monocotyledonous
plants. Here is a quote from the UK website by Dr Davey Jones at

"Strategy 2 - Monocotyledonous plants (grasses)

"This uses Fe complexing compounds called phytosiderophores to mobilize
Fe in the rhizosphere (see thesummary 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+ wher 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. "

A similar mechanism is mentioned for Strategy 1 plants:

"Strategy 1 - Dicotyledonous Plants 
This uses the plasma membrane H+ pump (see previous lecture) to acidify
the rhizosphere so that Fe becomes more soluble. This allows Fe-organic
complexes to form in the soil solution as the pH drops (Most Fe-organic
complexes are only stable below pH 6.0). The Fe-organic complexes then
diffuse to the root surface where they are reduced by the plasma
membrane ferric reductase to Fe2+. Fe2+ is then taken into the root cell
by a Fe2+ channel. The chelator is released and can return to the soil
where it can acts as a shuttle many times (see picture below). The root
can also produce its own chelators (e.g. the phenolic compound caffeic
acid or the organic acid citric acid). "

James mentioned peat. Yes, I believe peat is very effective in helping
to provide substrate iron. It can be TOO effective so it should be used
in moderation when used together with iron rich clay or other iron
additives like micronized iron.

Steve Pushak                              Vancouver, BC, CANADA 

Visit "Steve's Aquatic Page"      http://home.infinet.net/teban/
 for LOTS of pics, tips and links for aquatic gardening!!!