HYB: pigments (was: lycopene)

I assumed that anthoxanthin was a xanthone. Apparently it is a xanthophyll
instead.  TWOI mentions that ten different xanthophylls have been isolated in
iris, pp. 373-374.  The form "-xanthin" is normative to the Xanthophylls, so I
assume anthoxanthin is one of the members of this class.

The quite accurate and simple statement concludes the discussion there in
TWOI.  "It is obvious that much additional work needs to be done on all the
pigments of irises, not only to identify them, but also to make both
quantitative and detailed genetic studies." --TWOI, p. 374.

The presence of a number of different, but unidentified, xanthophylls is noted
from a 1974 study by West (TWOI, Appendix A, Table 3, p. 426-427)  Pigment
"q," one of the unknowns, occurring in quite a number of the varieties
studied.

Since Xanthophylls are sequential derivitives of Carotenes, continuing the
synthesis path that leads to beta- and alpha-Carotene, their presence is not
surprising.

As conservative as chemical synthesis pathways are across widely separated
species, specific studies on the question from almost any angiosperm may have
relevance, and any from irids in specific almost certain to have relevance in
describing what occurs in irises.

Commercially lucrative crops such a Gladiolus are far more likely to have
published studies of this nature.  One such to which I referred some time back
was a highly detailed study of the synthesis of anthocyanins in Gladiolus.
The significant fact from this study that struck me as being especially
important for us was that the synthesis was a fairly long, complex sequence of
twenty or more steps.

Each step is mediated by an enzyme catalyst--which is what DNA to RNA
sequences establish as their end product.  Twenty steps means twenty "genes"
are involved in the sequence.  It appears "blue" isn't simple "B" as a gene.

The TWOI "RRA" language makes more genetic sense, but I find it difficult to
grasp as I grew up believing in a simple "B."  The shift in perspective to
molecular (DNA governed) genetics hasn't turned out to be simple for some of
us older folk.  I hope the younger members and hybridizers find the new
approaches easier to grasp, as they (hopefully) won't have to unlearn a whole
lot of stuff that isn't true.

Molecular genetics makes a whole lot more sense out of such things as crossing
two whites and getting yellow, or, equally, two whites from pure blue ancestry
making violet-blue.  As it turns out, the "white" irises were non-yellow or
non-blue for different reasons--different steps in the synthesis chain
diverted or disrupted.  The crosses reestablish the "normal" sequence to
yellow or violet-blue.  Some of this was known even in the days of TWOI, but
the "why" has emerged since--with molecular explanations of a relatively
simple sort.

Neil Mogensen  z 7 in western NC mountains

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