Adventitious roots

[unknown at dl.ac.uk]

I have seen an unusual root response on Arabidopsis seedlings 
growing on a plate contaminated with a fungus which I thought 
might be of interest to those interested in root and 
hypocotyl development.  These seedlings were 2 weeks old, 
growing on 0.5X MS with 1% sucrose and a small amount of 
thiamine and had been contaminated for at least a week.  The 
primary, lateral and secondary roots were severely deformed 
and damaged by the fungal infection.  However, what I assume 
are adventitious roots were forming at various positions 
along the hypocotyls.  Each seedling had from 0 to 7 of these 
adventitious roots (average about 3).  These roots appeared 
to form from a tissue layer within the hypocotyl and then 
split the epidermis, and apparently an additional cell layer 
or 2, as they emerged from the hypocotyl.  The end result was 
a root emerging from a vertical slit in the hypocotyl about 6 
times as long as the diameter of the adventitious root.  The 
edges of these slits  were quite straight and uniform and 
they made it possible to view the inside of the hypocotyl.  
In some cases there were multiple roots (up to 3) emerging 
from a single slit.  The adventitious roots looked 
superficially like the normal roots of uninfected seedlings.  
I'm hoping someone out there can tell me whether this type of 
adventitious root formation is a normal response to fungal 
infection or (general stress) or whether this is something 
unusual.  Also, is this the normal way in which adventitious 
roots form in Arabidopsis?
 	
Thanks,
Tim Caspar
DuPont Central Research and Development