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Re: Analysis of MV's sedlings Part one Tangerine

  • Subject: [iris-photos] Re: Analysis of MV's sedlings Part one Tangerine
  • From: "Neil A Mogensen" neilm@charter.net
  • Date: Wed, 19 Jan 2005 16:07:31 -0500

Robin, this may show up in the sort by "Thread" far from your entry, but I did want to respond to your question about the beard, "white to cream tipped flame" or something close to that phrasing in the description of F o F.
 
The beard hairs are an extension of epidermal, top layer, cells of the fall, I think--although I am not totally positive of that.  In aril species it certainly is so, as the beard hair is of the epidermal cell, stretched upward, monofiliment--only one cell, which is part of the epidermis.
 
In Eupogons--bearded irises that fall in the classes other than aril--the beard hairs are shaped like a baseball bat, standing on the handle end.  They are composed of many cells, probably all epidermal in origin.
 
All the cells of the iris, all the way from the remotest root tip to the tip of the standards, have the same genetic makeup. 
 
What gets expressed, however, in any one cell depends on which genes are switched on, which are switched off.  An obvious example of this is that in normal development, you aren't going to see standards growing out of roots, or leaves emerging where the style arms are supposed to be.
 
We have pretty much ignored the whole question of switching mechanisms and control in our discussions of color, but in any iris, any color variation from part to part has to do precisely with those mechanisms.  Switching on, switching off "genes"--control genes--are what make plicata and luminata patterns possible, for example.
 
In beards, there must be similar mechanisms that make beard hairs different colors front to back of the beard, bottom to top of the beard hair.  In a hair or beard filament if the base is white, the middle is yellow, the tip is "flame," which may or may not be Lycopene present, what may be going on is that synthesis of carotenoids is suppressed entirely somewhere in a colorless part of the synthesis pathway.  In the yellow part I would assume, based on what Chuck Chapman has suggested, the synthesis proceeds to either a xanthophyll or beta-Carotene pigment, with the tip either containing some Lycopene, or more likely a heavy concentration of various yellow to richer than yellow Carotenes and/or Xanthophylls.  If tangerine (Lycopene) "tttt" is present, I would expect to see something more definite than what is in the "flame" description.  Many non "tttt" varieties have a hot color in the deepest part of the throat in the beard tips. 
 
I'd love to see a pigment analysis of those beard tips.  The result could be quite interesting.
 
Neil Mogensen  z 7 western NC mountains


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