Fwd: Re: Mycorrhiza

richard mcguiness armich at northcoast.com
Fri May 18 04:20:08 EST 2001

Good understandable working of mycorhizzia  in the root zone of a forest,
and chemically, on several articles here.  Check out " Troubles in the
Rhizosphere" and "A Touch of Chemistry".

Julia Frugoli wrote:

> >It is my understanding that the endomycorrhizae, known as Vessicular
> >Arbuscular Mycorhhizae (VAM), have very little host specificity.  In
> >other words, they will form symbiotic associations with many species
> >of plants, across family order and even class divisions.  It is
> >beleived that VAM are very ancient symbiotic relationships as they
> >are found in bryophytes, and pteridophytes.  This is exactly the
> >opposite of the rhizobium root nodules, which in some cases is
> >extremely species specific and with a few exceptions is found only
> >in the legume family (Fabaceae).
> >
> A clarification--most VAM symbionts are from the fungal order
> Glomales (Zygomycota), and only 200 species have been described, due
> to the difficulty of obtaining a culture with a sexual stage apart
> from their hosts (or even in contact with their hosts).  According to
> a recent review (Barker, Yagu and Delp, 1998, Plant Phys.
> 116:1201-1207) there is very little host specificity in colonization,
> but not all colonization leads to mutualistic nutrient exchange.  The
> fact that the number of fungal species present has a measurable
> effect on biodiversity and plant competition (van der Heijden, et
> al.,1998, Nature, 396:69-72) suggests to me that there is both some
> specificity and some positive effect, but as Mark pointed out,
> measuring it is no walk in the park.
> Plus, since it's possible to obtain plant mutants that no longer set
> up AM symbioses (Harrison, 1997, Trends in Plant Sci, 2:54-56) there
> is some specific signaling going on.  Interestingly, many of the
> legume mutants that are unable to set up symbioses with rhizobia are
> also unable to interact with AM fungi, suggesting the two processes
> share at least part of a common pathway.
> **********************************************************************
> **********
> Julia Frugoli
> Asst. Professor
> Biological Sciences
> Clemson University
> 132 Long Hall
> Clemson, SC 29634
> PHONE (864) 656-1859
> FAX (864) 656-0435
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