The People's Seed Bank

Marty Sachs msachs at uiuc.edu
Mon Dec 11 10:03:00 EST 2000


In article <976502878.730794 at cobalt>, Brian Sandle 
<bsandle at shell.caverock.net.nz> wrote:

> In nz.reg.canterbury.general Marty Sachs <msachs at uiuc.edu> wrote:
> > In article <976378882.461061 at cobalt>, Brian Sandle 
> > <bsandle at shell.caverock.net.nz> wrote:
> 
> >> In nz.reg.canterbury.general Tracy Aquilla <aquilla at bpmlegal.com> 
> >> wrote:
> >> > Brian Sandle wrote:
> >> 
> >> >> In nz.reg.canterbury.general Tracy Aquilla <aquilla at bpmlegal.com> 
> >> >> wrote:
> >> >> > Brian Sandle wrote:
> 
> >> Here again, then help me understand it. I can't get to the actual 
> >> paper.
> >> 
> >> High frequency of cytogenetic aberration in transgenic oat (Avena 
> >> sativa
> >> L.) plants Choi HW, Lemaux PG, Cho MJ
> >> PLANT SCIENCE 156: (1) 85-94 JUL 14 2000
> >> 
> >>    Abstract:
> >>    Cytological abnormalities were observed in transgenic oat (Avena
> >>    sativa L. cv. GAF/Park-1) produced by microprojectile bombardment 
> >> 
> >> {biolistic method}
> >> 
> >> of
> >>    mature seed-derived highly regenerative tissues. Of the plants from 
> >>    48
> >>    independent transgenic lines examined, plants from only 20 lines 
> >>    (42%)
> >>    were karyotypically normal (2n = 6x = 42) without detectable
> >>    chromosomal aberrations; plants from 28 lines (58%) had chromosomal
> >>    variation, i.e. aneuploids
> >> 
> >> {missing chromosomes}
> >> 
> >>  and structural changes. No significant
> >>    difference in cytological aberration was observed between the two
> >>    different culturing systems used for transformation: 
> >> 
> >> {after bombardment then method A:}
> >> 
> >> 57% chromosomal
> >>    abnormalities in plants derived from D'BC2 medium (2.0 mg/l 2,4-D, 
> >>    0.
> >>    1 mg/l BAP and 5.0 mu M cupric sulfate) used for tissue initiation 
> >>    and
> >>    maintenance 
> >> 
> >> {after bombardment then method B:}
> >> 
> >> and 60% in plants from tissue initiated on D'BC2 and
> >>    maintained on DBC3 (1.0 mg/l 2,4-D, 0.5 mg/l BAP and 5.0 mu M 
> >>    cupric
> >>    sulfate). Comparative differences in chromosomal status frequently
> >>    occurred among plants regenerated from the same T-0 line. The most
> >>    common cytological aberration in transgenic plants was aneuploidy,
> >>    followed by deletion of chromosomal segments; no change in ploidy
> >>    level was observed.
> >> 
> >> {now contrast with plants not bombarded for transgenics but still 
> >> raised
> >> the same subsidiary ways:}
> >> 
> >>  In contrast, nontransgenic plants, regenerated
> >>    from tissues comparable in age and culture media to that used for
> >>    transgenic tissues, had a much lower percentage of karyotypic
> >>    abnormality (0-14%).
> >> 
> >> {So transgenic 57% to 60% compared non-transgenic but same tissue 
> >> culture
> >> 0% to 14%.}
> >> 
> >>  Our data indicate that some stress(es) imposed by
> >>    the transformation process, e.g. osmotic treatment, bombardment and
> >>    selection, leads to cytological variation in transgenic oat plants, 
> >>    an
> >>    observation similar to that observed in our recent studies with
> >>    transgenic barley plants. (C) 2000 Elsevier Science Ireland Ltd. 
> >>    All
> >>    rights reserved.
> >> 
> >> 
> >> {And I should like to see the whole article, expaling that last bit
> >> further, of course.
> 
> 
> > OK, the proper control, to make your point, would have been cultured 
> > plants bombarded and treated exactly the same way as the transgenic 
> > plants, but without the DNA.
> 
> Do you, or anyone on the added newsgroup
> bionet.molbio.methds-reagnts
> know of any such controlled expts?


I don't know of any off the top of my head.


> 
>   Going through cell culture is only one 
> > aspect of stress generated variation.  The actual bombardment, osmotic 
> > treatment, and selection techniques also contributes to the variation 
> > the authors observed.  Technically, this 'extra' variation is not 
> > 'somaclonal' in nature, but due to other stresses.
> 
> So what do you call it something different when tissue culture is not the
> cause of it?


The more general term would be 'stress induced' variation.

> 
> 
>  The non-transgenic 
> > plants were simply derived from tissue culture without any of the other 
> > treatments, most of the variation in these was somaclonal.  
> 
> > Indeed, methods developed to transform plants with as little stress as 
> > possible would be preferable in that the less unwanted variation 
> > introduced, the better.  However, all breeding methods introduce 
> > unwanted variation that needs to be dealt with.
> 
> So the question is that if the biolistically, haphazardly, implanted 
> genes 


The genes introduced via biotech certainly aren't any more haphazardly 
introduced than those via genetic wide-cross.


> do not lead to extra variation (in some species more or less - that would
> be a hint to the haphazardness of the process also) at the 5% level in 
> the
> short term, will there be any later effect in the tortuous programmed
> pathways of evolution - say a Hox gene not showing its head until some
> pest is present, or whatever?


Certainly, no more so than genes introduced via a genetic wide-cross.  
Also, probably no more chance of this than finding a desired trait,  
that is caused a naturally mutated promotor, and using that in 
conventional breeding.


> 
>  >> >> The point is the extra instability of
> the transgenic results.}
> 
> 
> > Well, not exactly, the point is that the stresses introduced by the 
> > procedure can cause more variation than tissue culture does by itself.  
> 
> Have to look at whether it is the same sort of distribution as may be
> caused by promoters or enhancers starting to reside near genes
> unaccustomed to them.


Again, if this were a problem, this would also occur with genetic 
wide-cross.


> 
> > One way of limiting variation could also be bombarding directly into 
> > the 
> > meristem of an intact plant and thereby avoiding the cell culture 
> > aspect.
> 
> 
<..>
> > Here again, "Controls were 23 distinct clones produced from plants 
> > regenerated after the in vitro culture step used in the transformation 
> > protocol, but in the absence of the foreign gene (C1-control) and 41 
> > plants of the original sugarcane cv. Ja60-5 propagated as three-bud 
> > sets 
> > (C2-control)".  
> 
> > The 'C1-conrol' did not go through the entire same procedure as the 
> > transgenic culture (minus the DNA), which would have been required for 
> > your point.
> 
> > The papers you've cited indicate that that the entire procedure used to 
> > generate transgenic plants can result in more variation than tissue 
> > culture itself does.  However, these papers do not at all show that it 
> > is the integration of the transgene into the host genome that causes 
> > this variation.  There are several other stresses involved in the 
> > transformation processes used, that are more likely the cause of most 
> > if 
> > not all of this additional variation (again, this is technically not 
> > somaclonal; only that seen in the C1 control above that seen in the C2 
> > control is somaclonal).
> 
> > So, as with other breeding methods, there is unwanted variation that 
> > needs to be dealt with before a new variety with a desired introduced 
> > trait, goes to market.  The studies described, in the papers you've 
> > cited, will hopefully lead to methods of transformation that result in 
> > less unwanted variation that a breeder would need to deal with.
> 
> I think I have already answered most of that, but you admit improvement
> would be useful, 


Yes, I certainly agree that improvement in reducing unwanted variation 
would be useful.  You should note that in this regard, present biotech 
methods are a vast improvement over genetic wide-cross.


> and I claim that the precautionary principle should be
> used more in the mean time. 


IMHO, it is being used with biotech methods much more so than with other 
breeding techniques.


> Don't be basing the questions you ask on the
> shifting sands of the current financially driven economics.

I don't.

   -Marty Sachs






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