British, born in London

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Aim of this course Tell you about the research
of some ICU biologists Who I am Robert W. Ridge
B.A. B.Sc.(Hons) Ph.D. Professor of Biology, ICU
British, born in London University Western
Australia 1975-1978 Bachelor in Geology and
Geography 1978-1981 Bachelor in
Botany Australian National University 1982-1985
Doctorate in Genetics (PhD) 1985-1987 John Innes
Institute, England, Post-Doctoral
Fellowship 1987-1990 University of Tsukuba,
Foreign Professor 1990-1991 Ohio State
University, USA, Biotechnology Centre,
Researcher 1991-1993 Australian National
University, Rockefeller Foundation Fellow 1993-
ICU 1998 Visiting Researcher, Australian
National University 2002 Erskine Visiting
Fellow, University of Christchurch, New Zealand
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Lecture outline Lecture 1 Introduction Lectur
e 2 The role of nitrogen in the planet
The phenomenon of the Rhizobium legume
symbiosis Lecture 3 Basic cell biology how
the cell works Lecture 4 What I have studied
and researched Lecture 5 Root hairs and
experiments Lecture 6 Root hairs and
experiments Lecture 7 Gene transfer by
Agrobacterium as a tool in research (Prof
Williamson) REPORT Details later
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Research Field The biology of root hairs What
is a root hair?
White clover , Trifolium sp.
Vicia sp.
Arabidopsis mutant
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Research Field Contexts Agriculture - because
I work on legumes, a major crop Symbiosis -
because legumes have an intimate interaction with
a soil bacterium called Rhizobium, which invades
the plant via the root hair Pure Cell Biology
- because I study the root hair as a model plant
cell
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Agriculture Crop rotation Hundreds of years ago
farmers knew that some crops would put goodness
into the soil, and others would remove it. They
soon realised that if they grew cereal crops the
year after peas or beans, then they would get a
better yield.
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Growing the same vegetables in the same spot each
year can lead to problems. Soil living pests and
diseases, which thrive on that particular crop,
can build up in the soil to epidemic levels.
Vegetables also have various mineral needs and
continuous cropping of one particular crop can
lead to the levels of nutrients in the soil
becoming unbalanced. To prevent the build up of
pests and diseases in the soil and to help the
vegetables in their nutrient needs, crops need to
be rotated. Vegetables grow better in soil that
has been previously used for a different crop,
than in soil that has been used for one of their
own kind.
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It didnt take farmers long to recognise that
legumes have a distinct advantage, and the crops
after legumes grew much better. Farmers and
early agriculturalists knew that legume roots had
strange lumps on them, which they called nodules,
but it wasnt until late in the 19th Century that
scientists could show that these nodules had a
direct conenction with the excellent growth of
legumes in poor soils. I will return to legumes
and Rhizobium in a later class.
But remember that legumes are an important part
of your diet, and in some parts of the world form
the basis of diet, because they can grown on poor
soils and are high in protein. What legumes do
you eat every day?
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Symbiosis Living together. Originally termed by
de Bary for any intimate relationship between two
different organisms. Symbiosis can be divided
into three kinds of relationship a.
commensalistic (commensalism) one partner
living on the other with no obvious effect on the
second (literally eating at the same table).
Eg cockroaches in our houses, shrimps on crabs,
epiphytic plants (see tree by library north
facing side). There are thousands of examples !
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b. mutualistic (mutualism, symbiosis)
advantages for both partners cleanerfish get
food, cleaned fish avoids parasites and disease
ants cultivate caterpillars and aphids for honey
which are protected by the ants termites have
obligate symbiosis with protozoa, ruminants have
obligate symbiosis, so do humans with E.
coli. Plant symbiosis not so obvious, and often
involves the element Nitrogen.
Rhizobium/legume Azolla/blue-green
alga Gunnera/blue-green alga Frankia/Alnus
Mycorrhizae help in nutrient uptake
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c. pathogenic (parasitism, antagonism) One
partner living on the other with detrimental
effect on the second
Leaf Rust
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MOST ancient symbiosis was the incorporation of a
prokaryotic cell (ie a bacteria-like ancestor)
into another primitive organism, to make the
ancestor of the eucaryotic cell (the kinds of
cells that we and all higher organisms are made
up of).
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I want to explain some plant symbioses to you, so
that you get the general idea, and then in a
later lecture describe one symbiosis, the
Rhizobium legume symbiosis, in much more detail.
Gradually I will narrow down to my research
topic. This background information is very
important for you to understand why I do research
on my particular topic. Now I will discuss
briefly each of the following Lichen/blue-green
alga (fungus and plant) Azolla/blue-green alga
(plant and plant) Gunnera/blue-green alga (plant
and plant) Rhizobium/legume (bacteria and
plant) Frankia/Alnus (bacteria and
plant) Mycorrhiza (fungus and plant)
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LICHEN !!!
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LICHENS commensalism Mycobiont an
ascomycete Plant an alga Organic carbon from
alga via haustoria which penetrate algal cell
wall Alga have protection from dessication
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Anabaena (Nostoc) and the Azolla Symbiosis
Cyanobacteria, with the ability to both
photosynthesize and fix N2, are ideal pioneering
species. However, some occur in symbiosis with a
host including lichenous fungi, liverworts such
as Blasia, the aquatic fern Azolla, and the
angiosperm Gunnera. Of these, Azolla is the most
commercially important. Traditionally Azolla is
maintained and propogated in slow-flowing creeks
or overwintered in protected beds, then
introduced into paddies between plantings of
rice. The fern can then be either incorporated
before rice seedlings are transplanted, or left
to be shaded out as the rice canopy develops.
Yields in the subsequent rice crop are enhanced
by up to 1000 kg ha-1. http//waynesword.palomar
.edu/plnov98.htm
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A dorsal lobe of the water fern Azolla showing
the dark-green pocket filled with cells of the
microsymbiont Anabaena (Nostoc) azollae.
A filament of the cyanobacterial microsymbiont
(Anabaena Nostoc azollae) showing both enlarged
heterocysts and normal cells of the
micro-symbiont. Heterocyst frequency is greater
than 20.
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Gunnera sp. Botanic Gardens, Christchurch, NZ
Gunnera chilensis stem. Scales normally covering
the stem are removed. Glandular tissue where
symbiotic interaction with Nostoc occur are
numerous.
Gunnera - the only angiosperm that has a
symbiosis with a blue-green alga
Cross-sectioned stem from Gunnera chilensis in
light microscope, showing Nostoc colonies in
Gunnera symbiotic tissue beneath a stem gland.
Nostoc http//www.botan.su.se/fysiologi/Cya
no/Sub-1.htm
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Frankia and the Actinorhizal Symbiosis. Frankia
is an actinomycete forming N2-fixing
(actinorhizal) nodules with a range of
angiosperms.
Frankia is a Gram-positive, filamentous organism
characterized by multilocular sporangia and
N2-fixing vesicles in vitro. Vesicle production
occurs under conditions of N limitation, and in
the nodule, mature vesicles have a pronounced
lipid envelope that protects the nitrogenase from
oxygen. In the symbioses in which vesicles are
not formed (eg. Casuarina), lignification of
infected and adjacent cells results in formation
of an oxygen diffusion barrier.
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Strains of Frankia form root nodules on eight
families of dicotylenous plants (Betulaceae,
Casuarinaceae, Coriariaceae, Datiscaceae,
Elaeagnaceae, Myricaceae, Rhamnaceae and
Rosaceae). Infection is via root hairs in some
genera (Casuarina, Myrica), but proceeds
intracellularly in others (Discaria, Dryas,
Ceanothus). Nodules are perennial modified
lateral roots with lobes up to 5 cm in length.
Alnus glutinosa - there are examples on ICU campus
Alnus nodules
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Mycorrhizae http//www.blm.gov/nstc/soil/fungi/
Mycorrhizae are symbiotic soil fungi, present in
most soils, that attach themselves directly onto
the roots of most plants. They help the host
plants absorb more water and nutrients while the
host plants provide food for the fungi. Because
the surface area of the hyphae, the feeding
structures of the mycorrhizae, may be several
hundred times the surface area of the roots, the
mycorrhizae can feed on a larger soil mass than
the roots and they do so more thoroughly.
Mycorrhizae have the potential to be a central
nutritional source for the host plant.
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There are two basic types ectomycorrhizae that
associates on the plant surface only, and
endomycorrhizae, which can enter the plant cells.
One particular type is called VAM, Vesicular
Arbuscular Mycorrhizae.
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Jack pine mycorrhizae
VAM fungi
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Redwood trees grown without and with mycorrhiza
Mycorrhizal fungi enhance phosphorus uptake of
their host plants and their presence is more
prevalent in roots in low P soils. Mycorrhizas
also increase the uptake of other mineral
nutrients such as Cu and Zn. Mycorrhiza
formation has also been shown to confer drought
and disease resistance, reduce pest damage and
nematode infection, promote seed production, and
increase the fitness of plant offspring.
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The Symbiosis Between Legumes and Rhizobia
Legumes have been used in crop rotations since
the time of the Romans. However, it was not until
detailed N balance studies became possible, that
they were shown to accumulate N from sources
other than soil and fertilizer. In 1886
Hellriegel and Wilfarth demonstrated that the
ability of legumes to convert N2 from the
atmosphere into compounds which could be used by
the plant was due to the presence of swellings or
nodules on the legume root, and to the presence
of particular bacteria within these nodules.
There are different types of root-nodule
bacteria but for the moment can refer to them
collectively as rhizobia. The first rhizobia were
isolated from nodules by Beijerinck in 1888, and
shown to have the ability to reinfect their
legume hosts, and to fix N2 in symbiosis. Kochs
Postulate. http//waynesword.palomar.edu/trmar99
.htmrootnodule
Cell characteristics of Bradyrhizobium japonicum.
The cell measures approximately 2µm x 1µm.
Soybeans plus and minus Rhizobium
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Section through a nodule to show rhizobia-filled
cells
Lots of red nodules !
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Minus rhizobia Plus rhizobia