HYB: pigments (was: lycopene)

Donald Eaves asked if  betanin or anthoxanthin have been observed in iris.

In bearded irises, there is a discussion on p. 366-367 of TWOI concerning
Xanthones in general.  There are xanthones that act as co-pigments with
anthocyanins, at least one of which is a "yellow phenolic pigment, which
appears on paper chromatograms under ultra-violet light as an
apricot-colored....spot changing to a florescent yellow-green in ammonia...."
This dates from a 1963 publication by "Bate-Smith and Harborne."  There appear
to be a number of Xanthone pigments present in TB's acting as co-pigments with
anthocyanins.

I find it particularly interesting that JANE PHILLIPS owes its blue color
almost if not exclusively to the co-pigments and not to the anthocyanin
Delphinidin, which we often see referred to as "Violanin."

In addition, there is a table in Appendix A of TWOI on pp. 426-427 of various
pigments that had show up prior to the 1978 date of publication of TWOI in
chromatographic studies of a number of significant (now "historic") varieties
of bearded irises.  A number of these pigments and co-pigments are
"unknowns."

I've never seen a reference to betanin or anthoxanthin as such.  It is not
impossible that either or both may be included in the "unknowns" referred to
in TWOI.

Incidentally, I would like to refer back to a post by Carole Taber (I don't
recall the date) about the biosynthesis of Lycopene based on molecular studies
which supercede the information in TWOI by a couple of decades.  I quote the
original source (Buchanan, Gruissem & Jones, eds, *Biochemistry & Molecular
Biology of Plants*) in an article which, I believe, will appear in the October
AIS *Bulletin.*  Current studies in the biosynthesis pathways of carotinoids
suggest that the chain of synthesis goes from Phytoene to Lycopene in four
steps, like what is proposed in TWOI on p. 372.  The difference from TWOI lies
in the movement to beta-Carotene, our major yellow.

From Lycopene to both alpha- and beta-carotene involves a couple of specific
enzymes that "twist the tail" in Carole's words of the Lycopene molecule into
the beta or alpha form, depending on whether one (for beta) or both (for
alpha) are present and active.  The significance of this is a major change of
our understanding of "t" as a gene.  Instead of a conversion factor, it is a
preventor of conversion, making a very substantial difference in how we may
understand its history and origin, and how we can interpret the behavior of
the "t" factor in SDB hybrids.

The information in Buchanan, et al. does not mention gamma-Carotene, which
TWOI suggests is an intermediate form  between neurosporene and beta-Carotene
in an alternate pathway not involving Lycopene.  That does not agree with
present research, which shows Lycopene as a precursor to both alpha- and
beta-Carotene.  Gamma-Carotene itself may well be in a branching alternate
path from one of the precursors, either before or after Lycopene in the
synthesis sequence.

In case any of the newer readers don't recognize the acronymn "TWOI," it
refers to the AIS publication *The World of Irises* edited by Bea Warburton
and Melba Hamblen, major figures in the AIS world a generation or two ago,
neither still living.  A number of the writers whose work is included,
however, are still very active in iris work, including Keith Keppel, the
originator of this years Dykes Medal -winning variety,  CROWNED HEADS.  His
contributions to the work were substantial.

TWOI is still worth its price, by the way.  There are some copies still
available through the AIS Bookstore, the link to which is
http://www.irises.org/storefront.htm .  The book is presently priced at $15
and emphatically worth that reduced price despite its senior-citizen age.

Neil Mogensen  z 7 western NC mountains

---------------------------------------------------------------------
To sign-off this list, send email to majordomo@hort.net with the
message text UNSUBSCRIBE IRIS
Other Mailing lists | Author Index | Date Index | Subject Index | Thread Index