ancient corn

J.R. Pelmont Jean.Pelmont at wanadoo.fr
Fri Jul 11 07:59:55 EST 1997


Yuri Kuchinsky <yuku at mail.trends.ca> wrote (excerpt) :

> ....... No, not at all. You misunderstood me. I believe maize was native
> in America, and was brought to the Old World perhaps 3,000-2,000 years ago
> by ancient mariners. Certainly before Columbus, as evidence indicates. For
> non-specialists, please look at the photos of ears of maize in India on my
> webpage. For specialists, the genetic/botanical evidence should be most
> persuasive.
> 
> ...........
Thank you for your interesting information, correction and comments.

Are some remains of seeds being found in ancient sites ? This would be
very important to trace the ancient spreading of cultivated species such
as corn. The photographs are indeed puzzling. But don't you think that
artists may have created shapes and new objects with no special care for
exactness ? Especially in countries and different cultures, with a way
of thinking ans approach very different from ours. For instance in the
Middle Age, people would draw fantastic animals, such thiskind of
antelope with a long sharp horn in the middle of the front we call
licorne (I ignore the english word). India and Asia as a whole is fond
of symbols an imaginary world, with fantastic animals, monsters, etc.
Therefore it still puzzles me. It is an interesting observation, maybe
we need others such as remains of seeds, writings by travellers (Marco
Polo ?), and so on. Anyway archaeology is fantastic. Have you visited
Luqsor or Machu Pichu ? (I am just dreaming because almost on the leave
for vacation). ;-))

Following this, I had again a discussion with friends (Regis Mache,
Michel Herzog, Paul Mandaron) who are involved in the Arabidopsis
thaliana project or having worked with maize. A portion of about 80 kb
of the Arabidopsis genome has been sequenced here. The whole sequence is
expected for year 2004 or so.

As for maize again, the whole genome sequence is just too huge and out
of reach for this time. But the genome of rice is smaller, about 7-fold
the genome of Arabidopsis if I am remembering correctly. This work is
reported to be on the way (in Japan). This will be a very important
accomplishment for years 2100 (maybe), because geneticists will be able
to compare the genome organizations between a dicot and a monocot.

This type of work is fairly more advanced in the case of bacteria,
because their genome is small, about 4,500 kb (kilobases) long for E.
coli, about 1,800 for Haemophilus, even much less for Mycoplasma. The
complete genomic sequences of at least ten procaryotes are known
presently (some are not yet published), and more than 60 are on the way.
This will be a harvest of new knowledge about regulation, evolution,
....and discovery of new factors that have not yet been identified nor
isolated. Among eucaryotes, the genome of yeast (Saccharomyces
cerevisiae) is now known. Things are going fast due to this new
technology named shotgun sequencing, using both biochemical analysis and
computers.

Coming back to plants. Sequencing will be an essential challenge for the
future. When studying different cereal plants and other monocots,
scientists using standard genetic techniques have noticed that the whole
organization of the genome remained often quite similar from one species
to another, as for the general mapping of the chromosomes, the position
and distances of different well-known loci. Just as if large
building-blocks of information were carefully preserved and set end to
end in a defined order among the descent. This is of considerable
importance for a better understanding of the evolution of plants, of
grasses and especially of cereals that have been thoroughly modified and
transported by man all over the world. I heard that a lot of research
has been done about maize fertility. The job was to obtain varieties
that could not be auto-fertilized because the male inflorescence was
sterile. The lab in our nearby was involved in this project, but there
was a drawback, because the new varieties had become more susceptible to
a fungal disease, I heard. Anyway, although corn is grown in the alpine
valley where I am, the smallest corn-field in the whole region is just
under my office. It is a well-equipped room, with an automatic system
for light, water, and so on. A room for hybrid and transgenic corn.  And
light is powerfully glowing through the window part of the night (very
convenient for the parking space). :-)

For this time are known the complete sequences of chloroplast DNA in
various plants and algae : Marchantia, Euglena, tobacco, maize, rice and
some others (maybe spinach). Chloroplasts, which are considered as the
remnants of ancient endosymbiotic organisms closely related to
cyanobacteria, have kept some of the genes necessary for photosynthesis
and carbon processing in the so-called Calvin-Benson cycle. However many
former chloroplastic genes have been transferred to the nucleus. Genes
of procaryotic origin can still be recognized because of well-defined
features, such as codon bias and homology studies. In some instances, an
enzyme existing as different forms (isoforms or isozymes) exists
simultaneously in the chloroplast and in the cytosol. This has been
shown for glyceraldehyde-phosphate dehydrogenase (sorry for the bluffing
name), especially by Rudiger Cerff and coworkers in Hannover (Germany).
Proteins encoded by nuclear DNA are made in the cytosol and reach the
chloroplast using a principle that is now well-known on biochemical
grounds. How was genetic information from the endosymbiont captured by
the nucleus ? This is still a mystery, but extensive modern research on
this subject will certainly shed light on evolution at the chloroplastic
level. This is easier to do, because a chloroplastic genome is usually
in the 120-140 kb range, even smaller in other instances. The genome of
chloroplasts contains sometimes "pseudogenes", i.e. junk sequences which
are not used any more (?), and often many repeats. All these details are
investigated for a better understanding. Of course the same situation
holds for maize.

I understood that maize varieties grown by farmers are completely
artificially bred and selected, complicated hybrids that have become
very different from ancient or natural plants. To save the high yield,
auto-fertilization has to be excluded and the farmers have to buy their
seeds every year from companies, who make a lot of money with this (and
acquire some political and financial power as a whole in southern
France, I have been told so). The progress has been tremendous for the
last years. I do not remember the yield for corn. But the country is
still a big wheat producer in Western Europe. Some twenty years ago, the
yield obtained by farmers was only about 2.5 tons per 10,000 square
meters (we say hectares, sorry I do not know how many acres). This was
still too low for acquiring the seeds, fertilizers, fuel and risks. Now
the yield is reaching 10 tons and above, not only because of
fertilizers, but intensive hybridization and selection, especially by
the governmental organisation (INRA = Institut National de la Recherche
Agronomique). These efforts in many places are very encouraging for the
future, especially in the view of the rising population !

This is certainly an endless subject, with fantastic developments in
technology, economics, science and, as I understand, in history and
archaeology. As can be pointed out, fast moving molecular genetics are
offering new insights on evolution as a whole, as exciting as the
present performance of Pathfinder on Mars, and maybe even more costly,
if you imagine the great number of persons and scientific tools involved
in America and elsewhere.

Finally, I have the feeling that I went quite a bit outside the initial
problem of pre-Columbus corn in this post. Apologizing. As you see, we
can have plenty of good thinking or dreaming at coffee time, and this
was originally the Yuri Kuchinsky's fault !  :-)) Cheers.

____
P.S : If you intend to write again in this thread, I will be glad to
have a copy in my mail box, unless I may miss it, being away for some
time. Thanks.


-- 
jean.pelmont at ujf-grenoble.fr
Fax (33)0 476 51 4336



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