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
1993ICU
1998 Visiting Researcher, Australian National University
2002 Erskine Visiting Fellow, University of Christchurch, New Zealand
Lecture outline
Lecture 1
Introduction
Lecture 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
Research Field:
The biology of root hairs
What is a root hair?
White clover , Trifolium sp.
Arabidopsis mutant
Vicia sp.
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
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.
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.
It didn’t 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 wasn’t 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?
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 !
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
c. pathogenic (parasitism, antagonism) :
One partner living on the other with
detrimental effect on the second
Leaf Rust
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).
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)
LICHEN !!!
LICHENS: commensalism
Mycobiont: an ascomycete
Plant: an alga
Organic carbon from alga via “haustoria” which penetrate
algal cell wall
Alga have protection from dessication
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
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%.
Gunnera sp. Botanic Gardens, Christchurch, NZ
Gunnera - the only angiosperm that has a
symbiosis with a blue-green alga
Gunnera chilensis stem. Scales normally covering the
stem are removed. Glandular tissue where symbiotic
interaction with Nostoc occur are numerous.
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/Cyano/Sub-1.htm
Frankia and the Actinorhizal
Symbiosis.
Frankia is an actinomycete forming N2fixing (actinorhizal) nodules with a range
of angiosperms.
Frankia is a Gram-positive, filamentous organism characterized by multilocular sporangia and N2fixing 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.
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
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.
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.
Jack pine mycorrhizae
VAM fungi
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.
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. Koch’s Postulate.
http://waynesword.palomar.edu/trmar99.htm#rootnodule
Cell characteristics of Bradyrhizobium japonicum.
The cell measures approximately 2µm x 1µm.
Soybeans : plus and minus Rhizobium
Section through a
nodule to show
rhizobia-filled cells
Lots of red nodules !
Minus rhizobia
Plus rhizobia