Adventitious roots

Leonard N. Bloksberg bloksber at
Wed Jan 12 11:39:00 EST 1994

In Article <2h1a5d$54f at> """ <unknown at>" says:
> 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
I'm not sure about Ath, but in other spp this is quite normal.  The fungal 
infection induces ethylene production which enhances sensativity to auxins.
The auxins, in turn, induce adventitious roots.  You can also play with 
silver thiosulfate or norbornadiene (sp?) to inhibit ethylene in tissue 
culture, or try seeling plates/magenta boxes differently too.  I have 
measured ethylene concentration in tissue culture plates and magenta boxes
by flame ionization gas chromatography.  There are big differences depending
on wheather you use 2 vs 3 wraps of parafilm, or surgical tape, or other 
types of seals.  This has a radical (pun intended) effect on the response
of the explants to auxins and ABA.
	As for adventitious roots splitting the stem, again, normal.  In
my plant anatomy classes in college, we looked at many root primordia 
emerging from stem and root tissue.  It has always seemed a marvel to me
that they push through in such a brutal fassion.  Couldn't nature find a 
more gentle way to produce lateral roots?
	What all this means for Ath, I don't know, but in terms of general
plant biology, this is pretty standard stuff.
.		Good Luck
.	Leonard N. Bloksberg
.	bloksber at
.	Dept. of Crop and Soil Science
.	Michigan State University

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