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Plant Root Gravitropism

Plant Root Gravitropism

Literature seminar at the Babraham Institute, Cambridge, UK

Vladimir Kiselev

January 21, 2013
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  1. 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
  2. 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;
  3. 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;
  4. 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.
  5. 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;
  6. 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)
  7. DII-VENUS is a reporter for auxin abundance } Small changes

    from 1 to 5 nM are able to trigger DII- VENUS degradation
  8. 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
  9. “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;