that this simple transformation procedure can be extended to other cereals,” but this work
was never even repeated with rye. It is unclear what exactly led the authors to their con-
clusions, but the idea of transporting DNA through the vascular system to target the
male germ cells causes one to question the stability of the rye genome itself.
10.6.1.5. Electrotransformation of Germinating Pollen Grain.If the ideal trans-
formation system were available, it would be pollen transformation (Smith et al. 1994).
What could possibly be more convenient than simply introducing DNA into pollen and
then pollinating a plant to generate transgenic seed? Here is yet another report of pollen
transformation that has not been pursued or repeated in over 10 years. In this report,
pollen from tobacco was germinated, washed, and subjected to electroporation. Although
electroporation clearly works well for protoplasts and some actively growing plant
tissues, it may have its limitations for stable DNA introduction into pollen. DNA in the
growing pollen tube is not actively dividing and may not be receptive for foreign DNA.
The authors report the optimization of DNA delivery through transient expression of
gene activity, which is quite feasible as introduced DNA does not have to be incorporated
into the host DNA to be functional. Transient expression in germinating pollen is described
in this paper, along with molecular analysis of some of the recovered plants. The authors
report that 40–70% of the surviving pollen (electroporation kills 35% of the pollen) dis-
played transient expression and that one-third of the 743 plants, which were eventually
recovered, showed some activity from the transgene. This recovery rate is very high.
Although proper molecular analysis ofoneplant appears valid, comparative analysis of
more plants seems feasible and should have been presented, considering the large
number of plants recovered. See the next chapter for transgenic plant analysis methods—
we can see why these are so important in this section.
10.6.1.6. Medicago Transformation via Seedling Infiltration. Although a
relatively unknown plant outside of the plant sciences community,Medicago truncatula
has been presented as a “model” for legumes: the plant family, which includes alfalfa,
peas, and all of the “beans” (soybeans, lima beans, green beans, etc.). As a legume
model and potential counterpart toArabidopsis(which is the unquestionable model for
all plants), large amounts of resources were placed toward the development of comparable
transformation technologies forMedicago truncatula. These efforts resulted in a publi-
cation describing the development of theArabidopsisfloral dip method for this plant
(Trieu et al. 2000). Although most of the plant scientists on the planet have successfully
used theArabidopsisfloral dip method, replication of the work described in this paper
for this legume model have been nonexistent. Transformation efficiencies of 3–76%
were reported, but it remains unclear to this day whether any transgenic plants were actually
recovered. The appropriate molecular analyses were set up and are accurately presented in
this paper but they were grossly misinterpreted. As opposed to the one plant analyzed from
the pollen grain electrotransformation (discussed above), many different plants were
analyzed in this report. The difficulty lies in the patterns of DNA hybridization that were
presented in the paper. In most cases, hybridization patterns in transgenic plants should
be unique; in this paper, most of the plants displayed the same single band (see Chapter
11 for details). The criteria to be considered in evaluating the success of transgenic plant
production are not that complex. It is surprising that so many scientists are not fully
aware of them.
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