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HYB: Pigments 101


This is old hat to some of you, but I think it may give our newcomers a 
better understanding of why we have over-simplified things a bit.  If you 
haven't been through this exercise before, get out pencil & paper.  I'm going 
to present this in outline form but I think it will be a LOT easier to 
understand if you diagram it.....

At the top level, pigments can be divided into two groups, based on their 
solubility and where they occur in the cell:

I.  The pigments contained in the cell sap are water-soluble.   

II. The pigments contained in the plastids within the cell wall are 
oil-soluble.

And "never the twain shall meet."  One may be present without the other, or 
they may co-exist in the same flower.  Any interaction is an optical effect, 
though, not physical and not genetic.

At the next level, each of these two groups can be divided into chemical 
families.  Why bother?  Because the effect of a "gene" we hypothesize, 
whether it enables, inhibits, or modifies, is really an effect on the 
chemical pathway that changes the end product in such a manner that the 
difference can be readily seen.  

Now....

Going back to the group of water-soluble pigments, there are the flavenoids 
[I.A.] and the xanthones [I.B.].  

And going back to the group of oil-soluble pigments, there are the 
chlorophylls [II.A], carotenoids [II.B], and xanthophylls [II.C].

If you're diagramming, at this point you should have two boxes at the top 
level and five at the second level -- two under the first box and three under 
the second one. 

Now brace yourself, because we have to go down one more level before we can 
start talking about color in a meaningful manner....

The flavenoids themselves can be divided into five groups:  the 
anthocyanidins [I.A.1], leucoanthocyanidins [I.A.2], flavones [I.A.3], 
flavonols [I.A.4], and isoflavones [I.A.5].

The carotenoids can be divided into the carotenes [II.B.1] and lycopene 
[II.B.2].

If you've diagrammed this, you should have 7 boxes at the third level.  

So now we're going to go back and look at each end item, whether it's in 
level two or level three:

Anthocyanidins [I.A.1] produce a range of red through violet to blue.  There 
are six major ones, so they could be the subject of an entirely separate 
"course".

Leucoanthocyanidins [I.A.2] are colorless.

Flavones [I.A.3] range from colorless through ivory to pale yellow

Flavonols [I.A.4] -- little studied in iris, but they are know to lead to 
reds in other flowers.

Isoflavones [I.A.5] -- co-pigments, little studied and I can't find any notes 
regarding their effect on color tonight.

Xanthones [I.B.] are yellow, usually described as a co-pigment.  

Chlorophylls [II.A] are green.

Carotenes [II.B.1] range from yellow through yellow-orange.

Lycopene [II.B.2] is orange red in other plants, produces both tangerine 
beards in iris and the flamingo pink petals.

Xanthophylls [II.C].  Little studied in iris, but includes the carotene 
precursor phytofluene -- which could be another extensive topic.


If you're still with me, I have now described 10 families of pigments and 
co-pigments [co-pigments are more important for the effect they have on major 
pigments than in themselves]. 

Obviously, some of these are more important in iris hybridizing than others.  

Sometimes, the goal is to eliminate all but one family.  In our discussion of 
pinks, for example, we have concentrated on the carotenoids -- how to 
eliminate the other pigments, then the carotenes and end up with only 
lycopene. 

In others, it's a matter of combining complementary ones -- as in producing 
browns and blacks.


This strikes me as a good place to stop and entertain questions....

Sharon McAllister



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