Plant Root Gravitropism

Literature seminar at the Babraham Institute, Cambridge, UK

Transcript

1. Plant root gravitropism Literature seminar Vladimir Kiselev 21/01/13
2. How do roots and stems know where to grow?
3. Gravitropism A turning or growth movement by a plant or fungus in response to gravity.
4. Back in 1806 On the Direction of the Radicle and Germen during the Vegetation of Seeds Thomas Andrew Knight Philosophical Transactions of the Royal Society of London, Vol. 96 (1806), pp. 99-108
5. Back in 1880
6. Columella cells Gravitation is detected by sedimentation of amyloplasts at the bottom of columella cells
7. Cholodny–Went model • First model which described the mechanism of gravitropism in plants; • The model was independently proposed by Nikolai Cholodny (University of Kiev) in 1927 and by Frits Warmolt Went (California Institute of Technology) in 1928, both based on work they had done in 1926;
8. Cholodny–Went model • Auxin is the sole hormone that controls growth in gravitropism and phototropism; • Rate of growth depends on the concentration of auxin; • Both gravity and unidirectional light affect the movement of auxin;
9. Auxin • Pattern of auxin distribution is a key factor for for development of plant organs; • Complex and well coordinated active transport of auxin molecules from cell to cell throughout the plant body; • Plant can react to external conditions and adjust to them, without requiring a nervous system.
10. Auxin functions • Regulation of transcription of genes containing auxin responsive elements ! • Some impermeable auxins show their effects without entering the cell; • Sometimes auxin responses are too fast to be mediated by gene transcription; • Auxin regulates the abundance and activity of the plasma-membrane-located H+-ATPase; • Auxin regulates potassium and chloride channels and chloride-uptake transporters;
11. Auxin functions Auxin inhibit cell elongation, resulting in downward bending of the root
12. Model of the month
13. DII-VENUS -
    Aux/IAA-based reporter • DII is an auxin binding domain of Aux/IAA • VENUS is a variant of YFP • DII-VENUS is developed to be expressed under a constitutive promoter (in Arabidopsis thaliana)
14. DII-VENUS reveals changes in auxin distribution tip angle ~45° tip angle ~69°
15. DII-VENUS is a reporter for auxin abundance } Small changes from 1 to 5 nM are able to trigger DII- VENUS degradation
16. Model of DII-VENUS dynamics Parameter estimation BIOMD0000000413
17. Auxin root tip asymmetry
18. Auxin root tip asymmetry
19. Auxin root tip asymmetry • Auxin redistributes within 5 min of gravity stimulus • Root bending: ~10-20 min Once the root reaches ~40°, the auxin influx returns to equal levels
20. “Tipping point” mechanism • Auxin gradient exists only until the root bending midpoint; • The latter phase is driven by newly synthesized downstream targets of auxin response machinery;