Title: ARC Centre of Excellence
1ARC Centre of Excellence for Integrative Legume
Research How Legumes Make Nodules Lisette
Pregelj Education and Outreach Manager
2Legume Nodules
- Legume nodules are special plant organs that
house nitrogen-fixing bacteria called Rhizobium - Nodules form on Legume roots
- Nodules can also form on stems in some species
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4Vascular Bundles
Nodule Cortex
Sclerenchyma
Rhizobium Filled Cells gt25,000 per cell
Nodule Cross-Section
5Nodule Formation
- 1. Rhizobia attracted to root
- 2. Rhizobia attach to root hairs
- 3. Root hair curling
- 4. Infection thread formation
6Nodule Formation
- 5. Root cortical cell division
- 6. Rhizobia invade cortical cells
- 7. The nodule grows
- 8. Fully functional nodule
71 Rhizobia attracted to root
81. Rhizobia attracted to root
- Legume roots exude flavonoids
- (Soybean exudes the isoflavone genistein)
- Rhizobia are attracted to flavonoids
Bacteria turn blue when a reporter gene is
switched on by plant exudates (flavonoids)
Petri dish contains a bacterial lawn
92. Rhizobia attach to root hairs
Rhizobia
Root Hair
10 mm
102. Rhizobia attach to root hairs
Deformed root hairs
Curled root hair
Vascular bundle
113. Root hair curling
50 mm
124. Rhizobia infect root hair
Root Hair Curling
Infection Thread
Root Hair
Rhizobia
Infection Pocket
Legume Root
Vascular Bundle
134. Rhizobia infect root hair
50 mm
145. Root cortical cells divide
100 mm
155. Root cortical cells divide
100 mm
166. Rhizobia invade cortical cells
50 mm
177. The nodule grows
2-4 mm
188. Fully functional nodule
root
nodule
Rhizobia (green marker)
100 mm
19Nodulation Timeline
Roots
1-2 days post inoculation (dpi)
Inoculation (day 0)
4 dpi
4-6 dpi
10 dpi
3 weeks pi
20Chemical Signals
- Nodulation involved chemical signals
- Released by both the Legume plant and the
Rhizobium bacteria
Flavones
Nod Factors
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22Flavones and Isoflavones
- Released by Legume roots
- Signal Rhizobia in the soil that a Legume is
present and ready to nodulate - Soybean releases Genistein, an isoflavone
23Flavones and Isoflavones
Flavonoids in Root tip and Thickened root
24Nod Factors
- Rhizobia in response to flavones release Nod
factors - Nod factors are sugars with specific signalling
functions - Nod factors signal to a legume that Rhizobia are
present in the soil and ready to live in nodules
25Nod Factors
- Each Rhizobum species releases unique Nod factors
- All Nod factors have a concerved backbone
- Difference is in the decorations (R1 R2 R3 R4 R5)
and number (n) of sugar repeats
26Nod Factor Receptors
- Each legume species has receptors specific to a
unique Nod factor - Therefore each legume species nodulates with its
own Rhizobium - Soybean -Bradyrhizobium japonicum
- Lotus Mesorhizobium loti
- General Rhizobium NGR234
27CILR
- University of Queensland
- Australian National University
- University of Melbourne
- University of Newcastle
28CILR
- ARC Centre of Excellence for Integrative Legume
Research - Contact Us
- HQ University of Queensland
- Tel 3365 3550
- Email director.CILR_at_uq.edu.au
- lisette.pregelj_at_uq.edu.au
- Visit Our Website!
- www.cilr.uq.edu.au
29Picture and Diagram Credits
- Uli Mathesius
- Mark Kinkema
- Peter Gresshoff
- Dana Hoffmann
- Michael Sheahan
- Sureeporn (Ning) Nontachaiyapoom
- Paul Scott
- Brett Ferguson