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BEN # 223
BBBBB EEEEEE NN N ISSN 1188-603X
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BBBBB EEEEE NN N N BOTANICAL
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No. 223 May 4, 1999
aceska@freenet.victoria.bc.ca Victoria, B.C.
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Dr. A. Ceska, P.O.Box 8546, Victoria, B.C. Canada V8W 3S2
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HAEMOGLOBINS IN PLANTS
From: P.A. Guy <guy@cc.umanitoba.ca> and
R.D. Hill <rhill@ms.umanitoba.ca>
Haemoglobin is most commonly known as a protein that binds
oxygen in the blood of animals and transports and releases the
oxygen to respiring tissues. However, haemoglobins are in fact
ubiquitous in most organisms, including not only animals, but
also bacteria, protozoans, fungi and plants, where often their
functions have not been clarified.
Only in recent years has it become apparent that haemoglobin
proteins probably exist in all plants. These can be broadly
grouped into symbiotic and nonsymbiotic haemoglobins. The first
group has been characterised since the 1930s and include the
well studied `leghaemoglobins' found in the root nodules of
nitrogen-fixing plants. Nonsymbiotic haemoglobins, however, were
only identified during the late 1980s in the tree family, Ul-
maceae. They have since been studied in a range of dicots in-
cluding the legumes; monocot species from barley and wheat to
maize and rice and in the chloroplasts of algae.
All haemoglobins found across the spectrum of living organisms
can reversibly bind oxygen. Symbiotic haemoglobins are syn-
thesised in proximity to the plant's symbiotic partners and in
large amounts. The protein readily gives up oxygen and acts very
well in transporting and regulating oxygen supply to the plant's
microorganism associates. Nonsymbiotic haemoglobins differ
markedly in gene homology from the symbiotic and have been
detected in a range of tissues, often only under stress situa-
tions and in much lower amounts than found for symbiotic haemog-
lobin. Also, they generally show remarkably high affinity for
oxygen in that they will bind the molecule and keep it even at
very low cellular levels of oxygen. These characteristics dis-
count a role in facilitative oxygen transport and supply but
leaves the possibility of haemoglobin acting as an oxygenase in
a biochemical reaction. The question which remains is "What is
their exact function?"
To this end the work on the barley haemoglobin provides some
insight. It is synthesised in flooded roots and can be induced
in isolated aleurone layers when atmospheric oxygen is reduced
to 5%. It is also induced in the normally germinating caryopsis,
in both the embryo and aleurone, and in the root and shoots of
the young seedlings. In aleurones it has been shown that this
induction is a consequence of lowered energy (i.e. ATP) levels.
It appears therefore that at least barley haemoglobin is re-
quired during times when energy demands of the cell can not be
met by the availability of oxygen for normal respiration. This
hypothesis is further evident with the observation that maize
cells, genetically engineered to overproduce barley haemoglobin,
better maintain their energy levels when oxygen availability is
compromised. If the cells are engineered to eliminate haemog-
lobin, then they are unable to maintain energy levels under the
same conditions. This data provides valuable clues to the func-
tion and mode of action of nonsymbiotic haemoglobins in general.
The ubiquitous occurrence of nonsymbiotic haemoglobins in plants
indicates some fundamental roles in plant survival. From the
data for barley haemoglobin a role during transient waterlogging
or ice encasement can be envisaged, where oxygen availability is
low and there is a need to maintain energy levels. The plant can
resort to fermentation, or anaerobic ATP production, but in
doing so produces toxic compounds such as ethanol. Haemoglobin
may provide an alternative or complimentary route. This would
provide a plant able to synthesise haemoglobin with a distinct
selective advantage. As more data accumulates on other nonsym-
biotic haemoglobins, other roles may become apparent.
For more comprehensive reviews see:
Appleby, C.A. 1992. The origin and functions of haemoglobins in
plants. Sci. Prog. 76: 365-398.
Hill, R.D. 1998. What are hemoglobins doing in plants? Can. J.
Bot. 76: 707-712.
RE: BEN # 218 - SHOULD WE REJECT THE NAME 'SCIRPUS AMERICANUS'?
From: Adolf Ceska <aceska@victoria.tc.ca>
I was wrong to cite the ICBN [International Code of Botanical
Nomenclature], Article 57 of the Tokyo Code from 1993, when I
suggested that the name "Scirpus americanus" should be rejected.
At the time when Schueler made the typification of Scirpus
americanus, the ICBN did not have this article. The Seattle Code
(1969), effective at the time said: "A name is to be rejected if
it is used in different senses and so has become a long- per-
sistent source of error." The Example included in Article 69
implied that you needed the name to be "applied almost equally"
to two different species before it was to be rejected.
The next version of the ICBN, the Leningrad Code (1975), was
already phrased differently. Again, Leningrad Code Article 69:
"A name must be rejected if it has been widely and persistently
used for a taxon not including its type. Names thus rejected
shall be placed on a list of nomina rejicienda." Here the list
of Nomina Rejicienda for species names was first established.
Had the Intermountain Flora (published in 1977 and probably the
first major Flora that accepted the application of the name of
Scirpus americanus for "S. olneyi") followed that rule, it would
have used Scirpus pungens and Scirpus olneyi instead.
Retaining the name "Scirpus americanus" will lead to further
confusion, and the only logical way to minimize the damage is to
propose that name for rejection. This action, however, requires
a formal proposal to the Nomenclatural Committee of the Interna-
tional Association of Plant Taxonomists. If we reject "Scirpus
americanus" we will use S. olneyi and S. pungens without any
confusion. At the same time, all other combinations based on
"Scirpus americanus" will be rejected too. When we treat this
group of Scirpus s.lato as Schoenoplectus, we will use Schoeno-
plectus olneyi (A. Gray) Palla and Schoenoplectus pungens (Vahl)
Palla.
IMPORTANT LITERATURE DATABASES, AGRICOLA AND AGRIS, NOW ONLINE
From: Scott Miller <smiller@icipe.org> originally posted
on Entomo-l <entomo-l@listserv.uoguelph.ca>
Two major international databases of biological and agricultural
literature are now available for free on WWW:
AGRICOLA, including both the journal article database from 1979
to present, and the catalog of the USDA National Agricultural
Library:
http://www.nal.usda.gov/ag98/ag98.html
AGRIS, the FAO agricultural journal article database:
http://bwg.fao.org/agrisnew/
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