C3B—Lancaster Farming, Saturday, June 20,1981
BELTSVILLE To unprove a
crop plant, breeders traditionally
have had to rely on the rather slow
method of cross-pollinating
mature, flowering plants.
Breeders now have a short cut,
says plant physiologist Gideon W.
Schaeffer at a USDA-sponsored
symposium on plant reproduction.
Plant scientists are selecting
desired traits from small clumps
of tissue that have been grown in
the laboratory from pollen. The
technique is called anther culture.
Although it is a fledgling
technique, Schaeffer and his
colleagues at the Agricultural
Research Center in Beltsville, Md.,
have used it'to locate wheat and
rice plants that produce more of
the essential amino acid, lysine, in
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Plant scientists short-cut cross-pollination
their seed.
Finding this hereditary trait h\
anther culture takes only about
one-third the time of current
methods. And the work can be
confined to one laboratory instead
of several acres of land, Schaeffer
told members of the press
Anthers, which are the pollen
producing organs of plants, are
placed in a sterile growth medium
and subjected to chemicals that
inhibit the growth of all pollen cells
that do not have the desired
hereditary .trait. Those that sur
vive presumably contain the genes
for the desired trait, and they are
then generated into new plantlets.
The technique works by virtue of
the fact that the anthers’ pollen
grams are the male sex of the plant
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world and, thus, contain half the
normal number of the plant cell’?
chromosomes. Genes on these
■chromosomes do not have any
competition from genes on a
partner chromosome which might
repress a desirable hereditary
trait, as for example, genes for
tallness and shortness found in the
same pea plant over a century ago
by Gregor Mendel. With anther
culture, says Schaeffer, “What you
see is what you’ve got.”
Another advantage of anther
culture is its ability to produce
plants with uniform chromosomes,
which produce uniform seed when
self-pollinated. When clumps of
pollen tissue are induced to double
their chromosomes, the new
plantlets contain pairs of
chromosomes that are identical.
To achieve this uniformity by
current breeding methous,
breeders have to backcross the
planrcontaimng the desired trait
several times with parent
generations.
Schaeffer, who coordinated a
session entitled “Transfer of In
formation and Genetic Interplay”
during the 3-day Beltsville sym
posium, highlighted several
speakers’ presentations. The
session dealt with the role of
various processes in evolution.
University of Illinois geneticist
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Jackß. Harlan reported that small
pieces of DNA control the heredity
of plants not by behaving as' genes
themselves but by regulating the
expression of genes. These DNA
units can move from a site on a
particular - chromosome to any
number of - sites on other
chromosomes, switching nearby
genes on or off, Schaeffer ex
plained.
The gene regulators may be as
important in affecting the heredity
■ of plants as the recombination of
chromosomes during cross
fertilization, especially in crosses
between two distant species of
plants. They are probably more
important than mutation followed
by natural selection in speeding up
the evolutionary process, Harlan
asserted.
Schaeffer said that this theory
could account for some unexpected
traits that have appeared in his
own work with anther culture.
Looking down the road, Schaeffer
foresees the day when gene
regulators may be inserted into
chromosomes at the desired site by
recombinant technology.
Professor H.F. Linskens from
The Netherlands’ University of-
Nijmegen, Department of Botany,
and professor Robert Omduff with
the Department of Botany,
University of California at
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Berkeley,- pointed out several
factors that seem to limit the
ability of plant species to adapt to
the pressures of evolution,
Schaeffer said.
t For example, plant species that
are able to outcross—exchange
genes' with other species—
theoretically would have a greater
chance for survival because they
have a larger gene pool to draw
from. Hollies, for instance, which
have male and female
reproductive' organs on different
plants, have the greatest chance
for variability in thdir genes. But
hollies and other dioecious plants
are the exception rather than the
rule in the plant world. Many
species have evolved with rather
narrow reproductive habits. Some
can only reproduce vegetatively.
Linskens described certain plant
species that exclude potential gene
donors by the structure of their
flowers or by a lchemical in
compatibility. similar-**) the im
mune reaction in animals.
In speculating on why certain
species limit their ability to adapt,
Qmduff said that the reproductive
systems of plants more likely
evolved because of an advantage
conferred on the species in the
past, rather than for any future
advantages they may offer,
Schaeffer reported.
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