Re:Marcotrigianop not good enough?

I wrote a post to Dr. Marcotrigiano asking for his personal opinion
regarding
the role of mitotic recombination as a causal factor for variegation in
hosta. He replied to me within 30 minutes of my request. Now that's what
I call a friend. I will let you read my request for his advice and his
answer. This post should answer any questions about the validity of
Ben's unorthodox theories about the origin of sports in hostas. The
floor is open for further discussion if there is any doubt. I don't
suppose there will be any eating of hostas because of this matter.

Jim Hawes
......................................................
Dr. Michael Marcotrigiano's post to me follows:

Somatic recombination to give spots can only occur if the heterozygous
is
codominant yellow. You could not get twin spots unless the background
heterozygote was an intermediate color. But this argument is senseless
anyway. The inheritance of variegation in hosta is maternal and
dependent on
a mottled mother that has not undergone plastid sorting out as would be
the
case in marginal variegation. All of the inheritance data suggest a
plastid
mutation, not a nuclear mutation. If he means the plastid mutation is
from
recombination in the plastid genome, well that is a different story -
but
still very unlikely. The overwhelming cause of variegation in plants is
a
mutant plastid producing a mosaic cell, producing mosaic eggs. The
eventual
sorting out of plastids within each stratified cell layer caused a
stable
phenotype and usually makes eggs that have either white or green
proplastids
but not both. That is why so many marginally variegated plants produce
only
white seedlings that die. Vaughn would back me up on the inheritance in
Hosta. If Hosta are variegated for any other reason but plastid sorting
out,
I'll eat my Hosta!

*************************************
Michael Marcotrigiano
Director of the Botanic Garden
Smith College
Northampton, MA 01063
email:mmarcotr@smith.edu
http://www.smith.edu/garden
http://www.science.smith.edu/~mmarcotr
voice: 413-585-2741

-----------------------------------------------------------------------------------

"We come from the earth,
we return to the earth, and
in between we garden"
Nelson Eddy


>>> Jim Hawes <hawesj@atlantic.net> 03/13/01 11:20AM >>>
Hello again Michael,

I promised myself (and you) that I would not communicate excessively
because you were very busy. This message is because of embarrassing
circumstances and you are somewhat involved.
Let me explain.

I described earlier that I had begun a technical discussion on Origins
of Sports in Hostas via email involving several interested friends.
During the last three weeks we have discussed your article "Chimeras and

Variegation: Patterns of Deceit"...also articles by Dr. Kevin Vaughn on
chloroplast mutants in Hostas and the literature review of plant
chimeras in tissue cultureof Dr. Lineberger of Texas A&M.

One of our participants, Dr. Ben Zonneveld of Leiden University in
Holland, has written three articles since 1996 on the causes of sports
in hostas. He lists three causes as mitotic recombination (somatic
crossing- over of chromosomes), chimeral rearrangements (tissue
transfer) and nuclear mutations. He says practically nothing about
chloroplast mutations sorting-out, the role of apical cell initials and
the related role of LI and LII tissues in leaves. He refuses to answer
questions or make references to the work of others. I have tried to
"interprete"' your explanations of the genetic changes in nuclear and
chloroplast genome and related  phenomena responsible for origins of
chimeras using layman's language as much as possible. I believe I have
had  a good basic understanding for the last two or three years of your
concepts as described. Up to this point no one has mentioned mitotic
recombination as a causal factor for chimeras. When Ben Zonneveld read
your article for the first time, perhaps , and saw the photo on page 773

of the yellow leafed  tobacco with green and white twin spots,
attributed by you to be caused by somatic crossing-over, Ben made the
argument that this specific reference was proof that his theory of
mitotic recombination as a causal factor for certain sport sequences was

valid....i.e. that of yellow leaves on hosta with a green edge was
caused by "mit rec". My comments were that this was not necessarily so.

What I would like to ask of you is a very brief statement from you
regarding the relevance of somatic crossing- over as a phenomenon in
plants ( in hostas specifically, if possible) to explain how it may or
may not "explain" the origin of chimeras in hostas. I can think up some
theoretical explanations but a statement from you will help resolve this

serious " sticking point" in our discussion.

Please drop a short post if you can but only  when it is convenient. I
need your help on this.

Jim Hawes



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