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Re: Reasonable questions



Reply again to dale!

Dale Wilson wrote:

Hi Joe,



What we are talking about in the above example is how does the
transgene slip through, and how much is expected to do so.





The main point is that  the endosperm is a major contributor
to good transgene pollution in corn and oil seeds. I asked you for
studies supporting your belief that embryo is a richer source of
transgens than endosperm.



The endosperm contains less total DNA per unit dry weight, and, as you
have pointed out, the DNA it does contain is 2/3 maternal (as opposed
to 1/2 maternal in the embryo).  So in normal grain contamination
situations, somewhat more transgenic material will come from the
embryos.

answer:
I have hunted for journal articles that support your views on  maize
embryo and endosperm., but my  reading of journal articles  contradicts
your  data and conclusions. For example , the paper below used genetics
to  show that grain filling mutations  can vary number of endosperm
cells relative to embryo. The authors found  mutations decreased
endosperm cell number and grain mass(and mass including DNA) by as much
as two thirds relative to embryo. Since the embryo deficient kernels
were viable  it indicates that sufficient endosperm remains. Those
observations pretty much agree with microscope cross sections of corn
grain indicating that endosperm cells far outnumber embryo cells. What I
am saying is that the journal reports seem to clearly show that maize
kernels  contain more endosperm than embryo.
Volume 23, Issue 1, July 2000 Plant Journal pages 29-42
rfg1, a mutation reducing grain filling in maize through effects on
basal endosperm and pedicel development. M. Maitz, G. Santandrea, Z.
Zhang, S. Lal, L.C. Hannah, F. Salamini and R.D. Thompson
I am reminded of your earlier comment that regulators base their
evaluation of corn transgene  pollution on a proportion of polluted
grains. I would appreciate the names of such regulators so that we may
challenge their bizarre notions. Finally, I again ask for a journal
article that shows your figures on maize embryo and endosperm.


But it doesn't matter.  Overshadowing this concern is the fact that the
embryo/endosperm ratio is pretty much constant (except for high-oil
corn).  So in most situations transgene contamination by weight will be
roughly proportional to the frequency of contaminated kernels.



I was not trying to split hairs on the quantitation.  If 0.5% of the
kernels in the grain are transgenic, then the weight percentage of
the transgenic grain might be slightly different (maybe .48 or .52%)
for the reasons you cite.

Answer:As I pointed out above your figures do not seem to agree with
findings published in journals.






Your numbers imply that embryo is much richer in transgenes
than endosperm in the seed and that is very unreal.

Answer: again show me the journal articles.




Because the embryo/endosperm ratio is pretty much constant, none of
that matters.  If one batch of corn kernels is 1% transgenic (on the
basis of kernel numbers), it will contain X milligrams of transgenic
DNA per kilo.  Another batch of corn kernels with 1% transgenic kernels
will also contain approximately X milligrams of transgenic DNA per
kilo.  The reasons this is so include:

1. generally all these contaminants are hemizygous
2. the endosperm/embryo ratio doesn't change very much.



for embryo and it is much larger than embryo. How much larger is one
of the studies that should have been required by APHIS, but ignored
for fear of the answer.



I feel like this is an exercise in hair-splitting.  The much bigger
factor in practice is what pollen is blowing from where into your
conventional corn field.

Answer; I feel that the exercise  amy not be in hair splitting but in
obfuscation. Please do show me the journal references as I have shown
you mine!
Sincerely, Joe


Dale

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