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RE: Analysis of MS seedlings -Flavanoid

  • Subject: [iris-photos] RE: Analysis of MS seedlings -Flavanoid
  • From: "Neil A Mogensen" neilm@charter.net
  • Date: Wed, 19 Jan 2005 16:50:35 -0500

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 that Robin asked, as you also have, Chuck.  My reply is so far back on the thread list/sort that I am posting it again here.
 
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.  Since the arils are evolutionarily derived from Eupogons (presumably, assumed because of the reduced chromosome complement and the presence/absense of metacentrics in the karyotype)
 
In Eupogons--bearded irises that fall in the classes other than aril--the beard hair is 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, or has a flavonoid expressed there, with the tip either containing some Lycopene, or more likely a heavy concentration of various yellow to richer than yellow Carotenes and/or Xanthophylls and /or flavonoids.  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.
 
Some of the earliest "tttt" varieties were not recognized because the color was so muted with other pigments present that the "pink" and "tangerine" are only recognized in retrospect, so blended pigments where Lycopene is minimally expressed along with other yellows or pale anthocyanins could give some rather ambiguous results. 
 
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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