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Re: Discussion on Origin of Sports


Back to where I left off last night.  I think we can dismiss a few
ideas for variegation as being unlikely, and we can accept that at
least some variegation is mutated chloroplasts.  What I don't have a
good answer for is that L1-L2 variegation that shows up when the seeds
germinate.  And the other thing I don't have a good answer for is the
different sports that can and do show up from existing variegated
hostas.  If variegation was the result of only mutated chloroplasts,
then we should only see at best 5 possible sports from L1-L2 shifting
and rearrangment.  If we start with a albomarginata type then we can
get an all green form, an all white form (dies), a
albo-mediovariegated type or a streaked form.  Allowing for some minor
differences because of growth rate due to lower photosynthesis in the
non-green parts, these plants should pretty much look alike.  However,
we see many different sports showing up that have changes in addition
to the variegation patterns.

I was out of commission  yesterday participating in a one- day surgery
date with a Doctor on a basal cell carcinoma excision from my chin. I'm
home again, OK,  after the simple surgery and willing to try to
address.....( I didn't say answer) some of the excellent questions you
raised. As I read the questions , the thought occurred to me...YES,
Marcotrigiano discussed these issues so let me try to repeat
Marcotrigiano's views in slightly different language.

The essence of his explanation for variegation in chimeras is that THE
used them again for emphasis.) He does not say that nuclear mutation do
not occur. I think that Bill Meyer yesterday tried to explain this point
also ...that there are indeed most likely many nuclear  mutations that
are unseen or that may not be very noticeable...and that these most
likely affect "form" characteristics of many types.

Let's go back to  Marcotrigiano's description of stochastic sorting out.
He stated that TIMING of when the sorting out began determined the
variability within the population of the plastid mix undergoing sorting
out . To me this explains that if the sorting out is incomplete, the
population mix of green unmutated plastids and the white ( oe other
colored) mutated plastids will be different from cells where it is
complete. This difference may determine the color of the  mutant cell. (
See the Hosta Color Wheel for suggestions of the many variable colors
possible .)We are mixing paint again as on the Artist Palette. Just
about any color (green, thru yellow and white)  is possible in various
LI and LII tissue, depending on the timing of  when the  sorting out
began and became complete.I am saying this using my words to interprete
the expressed  meaning of Marcotrigiano's concept.

The same explanation applies to the case of seedlings. Their colors will
be those that result from the various porportions of the mutated and non
mutated proplastids in the egg cells. Timing of the sorting out is the
variable that determines the porportion of the plastids within the mix.
Please understand that I am not being dogmatic about this. I am only
trying to find the most reasonable explanation  based upon the
scientific generalizations provided by Marcotrigiano.and coworkers on
what has been observed in most genera studied so far..
One of  the experiments I am trying to do
is to induce sports and then take those sports and induce more sports
and see how these different lines relate to each other.  We can't be
getting these sports showing up that also have major changes in
phenotypes unless there is something else going on.

My own hunch is that transposible elements are playing a role or there
is some control mechanism at work that is linked with histogenic layer
formation.  The histogenic layers are formed fairly early on in the
development of the zygote.  It's possible that genes for chlorophyll
synthesis or other regulator genes are turned on or off at this time.
 Transposible elements seem to play a role in the streaked variegation
in some flowers, so I don't see why they couldn't also play a role in
hosta variegation.  The problem we face right now is that we really
don't have enough knowledge to say anything specific.  This is why I
think we need some LONG term studies.  It may be possible that some of
us who are interested in this can cooperate somewhat and report on
results we observe this year when hosta seedlings start to germinate.

Joe, I agree that we don't know enough about variegation in Hostas.yet.
Marcotrigiano does indeed mention transposable elements as responsible
for generating periclinal chimeras in maize and Ipomea. I agree that
reseach is necessary for determining if this causal facor may be
applicable in Hostas as well.

I have enjoyed the discussion so far and I imagine you have also. And we
may not even be finished yet. I have a bit more to add when the timing
is right,,,just like the sorting out, right?
Jim Hawes

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