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Re: HYB: Pigments 101


Thanks Sharon for your notes on genes. Just an added note on Anthocyanins,
irises (at this stage) do not produce the two reddest forms, perlagonium and
peonadine (excuse spelling, I don't have my references handy at the moment)
leaving just the blue, purple, rose range of colours. I beleive that the
only true reds will come when the enzymes that control anthocyanadins are
mutated (naturally or otherwise) to produce peonadine. If we just
concentrate on the plastids colour ie lycopene and try to produce that over
a non antocyanadin colour the white refraction from the cell sap will reduce
your lycopene colour to pink. Unfortunately  plants that produce at the
truely red end of the anthocyanadin range do not also produce true blues and
vice versa. Hence there is still no true blue rose.

Re your notes on variation of colour expression. I have noted that there is
a little year to year vartiation, I'm sure my clear blues such as Scented
Bubbles are a little more violet this year.

My biggest confusion is one called Binalong. In one part of the garden the
falls appear so dark a brown as to be almost black. In another the falls are
dark brown but it it nowhere near black. The lighter coloured ones are a bit
larger blooms so there is probably a bit of a dilution factor but the colour
difference is very noticable.


Colleen Modra
South Aust.

----- Original Message -----
From: <arilbredbreeder@cs.com>
To: <iris-talk@egroups.com>
Sent: Monday, November 27, 2000 5:17 AM
Subject: Re: [iris-talk] HYB: Pigments 101


> In a message dated 11/26/00 6:28:00 AM Mountain Standard Time,
> charmike1@juno.com writes:
>
> <<
>  How is this modified (?) or whatever when people report varying hues or
>  tints of the same iris in different regions and/or soils? I really am
>  only partially awake folks but I've been wanting to ask that question for
>  several days now!  >>
>
> Ahhh....   So we want to talk "nature vs. nurture" now?   It helps to
think
> of genetics as defining the potential, environment as influencing its
actual
> expression, and observers as affecting the reporting/analysis/conclusions.
>
> Let's start with the Photo Factor -- no film accurately captures all
colors
> and further distortion usually occurs during the printing process.  A
report
> that "It doesn't look like that in MY garden!" can't be taken at face
value
> if 'that' is a photograph -- whether seen in a catalog, book, or slide
show,
> or especially on a website like mine [which could be another thread
> entirely!].  Observations need to be human-eye-on-actual-flower.  The SAME
> human eye, with observations close enough together in time to avoid
problems
> of memory distortion.  If you saw something in bloom in your own garden
one
> spring, saw a picture of that same cultivar during the year, and then saw
the
> flower again in a display garden the next spring -- can you be sure the
> memory you are drawing on hasn't been influenced by the picture?
>
> To get comparable colors for seedling records, I used the same type of
film,
> the same lab, and instead of taking pictures throughout the day as each
> flower reached peak form, I'd shoot a full roll in late morning when the
> day's flowers had opened but not started to fade.  That provided
consistent
> lighting conditions for each roll and to compensate for processing
variations
> I included a shot of the Macbeth Color Chart. [You should have heard the
> lecture a new employee at the local camera shop got when he took it upon
> himself to save me a few cents per roll by sending my film to a processor
> other than the one I'd specified.  I had the shots of the color chart to
> prove their processing wasn't as accurate and the owner had show 'n' tell
> material to explain the tradeoffs between quality & cost.]
>
>
> Removing the Photo Factor, we also remove much of the Myth. Now, assuming
> that we're dealing only with first-hand observations, there are factors
that
> really do affect the expression of pigments:
>
> pH -- the expression of some anthocyanidins is affected by pH.  Hydrangeas
> are probably the best known example.  There have been reports of this
effect
> in iris, to a lesser degree, but although my own observations suggest that
it
> is a factor I'm not aware of any definitive studies.
>
> Sunlight & Temperature #1 -- strong sunlight and low [but above freezing]
> temperatures during bud formation increase the intensity of pigments,
> especially the yellows.  I picked up this tidbit from a friend who had
been
> in the greenhouse business and found that it did, indeed, explain
phenomena
> occuring in my iris gardens. [One spring, we had a couple of weeks of
> overcast days during bud formation and WHITE CHOCOLATE's normally dark
> chocolate beard was merely a yucky brownish-violet.]
>
> Sunlight & Temperature #2 -- after the flower has opened, strong sunlight
and
> high temperatures can hasten fading.   It's very hard to separate these
two
> factors, because beds with the strongest light also tend to be warmer --
but
> I've been able to set up controlled experiments where the ONLY difference
was
> the amount of shade and those in partial shade held the color much better
> than those in full sun.
>
> Water/Expansion -- arilbreds, expecially, are noted for continuing to
expand
> after the flower has opened and thus to undergo dilution of color.  I've
> noticed a similar, although less pronounced, effect in TBs.  If they don't
> get enough water, the last flowers to open are both smaller and more
> intensely colored when they first open.
>
>
> These are just a few factors to start the discussion, I'm sure others can
> think of more.
>
> Sharon McAllister
>
>
>
>


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