- symbiotic N2 fixing bacteria lives in the plant root nodules (anaerobic) in poor N2 conditions
- bacterias (eg. leguminous, Rhizobia - symbiotic, cyanobacteria - free living) give plants with fixed N2 and plants give bacterias with nutrients and carbs.
nodules provide anaerobic conditions by:
- low gas permeability
- leghemoglobin
plant gives:
- nodule
- leghemoglobin - oxygen transport
- nutrients
bacteria gives:
- fixed N2 via Nitrogenase enzyme
- heme part of hemoglobin
Nitrogenase rxn:
N2 + 8Fdred + 8H+ + 16 ATP 2NH3 + H2 + 16 ADP + 16Pi
by redox rxn in Fe protein and reducing MoFe (iron-molybdenum) protein.
Rhizobial genes participating in nodule formation
= nodulation (nod) genes
Summary of infection process / Establishing the symbiotic relationship
1. FLAV (flavonoid) is a chemo-attractant that attracts bacterias to secrete Nod D genes.
2. Nod D genes bind to promoter of Nod A,B,C genes
3. Nod factor LCO (LipoChitin Oligosacharides) is expressed
4. LCO binds to lectin receptors in plant root hair
5. bacteria attaches to cell wall of root hair
6. root hair curls due to Nod factors
7. cell wall degrades and bacteria have access to plant plasma membranes
8. Golgi vesicles fuse and extends plasma membrane to form the infection thread towards the root cortex
9. cells deep in root cortex differentiate and divide - initiates nodule formation
10. infection thread branches and moves towards developing nodules
11. bacteria enclosed in plasma membrane are release into nodule
12. bacteria starts to differentiate and divide and becomes bacteroids - N2 fixing symbiont organelles in root epithelial cells
13. nodule elongates and differentiates, including vascular system surrounds bacteroids so it's possible to transfer nutrients and fixed N2
14. layers of cells form to prevent O2 from entering.
15. Nitrogenase enzyme and leghemoglobin are synthesized
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