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Integrating soil and plant knowledgeat different scales to betterunderstand the dynamics
of water in SPAC
Nottingham, 11 September 2008
G. LOBET, L. PAGES, F. CHAUMONT,M. JAVAUX & X. DRAYE
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Plan
Context
Material and methods
Results
Discussions
Conclusions
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Context
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Water movement in plants
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Several resistances:
- in the stomata- along the xylem vessels- uptake by the roots
Soil-Plant-AtmosphereContinuum
Water potentialgradient
Water movement
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Aquaporins increasemembrane permeability
- increase the water flow ratethrough the membranes
-ZmPIP2:5 mainly present inendoderm and exoderm of maize
roots
Aquaporins
5
To test the quantitative contribution ofZmPIP2:5 at the root system level
From: Hachez et al., 2006
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Material and methods
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Material
Three tools were used:- transgenic plants deficient inZmPIP2:5- rhizotrons- light transmission imaging
To get picture of the water
distribution inside de rhizotronsat a low time scale
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Methods
Six rhizotrons- 3 Transgenic + 3 Wild-Type
When plants are 30 days old:- substrate at the field capacity- water supply is stopped- light transmission imaging every 2 hours during 2 1/2 days.
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Results
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Growth parameters
Shoots:- similar growth rate for all the plants
Roots:- two groups:
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Deep Superficial p-value
Depth (cm) 75.0 + 8.66 48.3 + 7.64 0.016 *
Growth rate(mm/day)
19.21 + 7.65 11.53 + 4.15 0.008 **
intrinsic variability
of the growth rate
Trangenics Wild-types p-value
Depth (cm) 61.7 16.1 60.0 17.3 0.909
Growth rate(cm/day)
16.7 6.8 11.6 4.9 0.352
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Transpiration
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During the day- effect of stomatal regulation
Across days- water less available- roots less efficient
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Aquaporins
Western Blot at the end of the experiment:- no differences between Transgenics and Wild-Type
Morphological differences
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Variation of the expression of the silencing?- Influence of the temperature
Trangenics Wild-types p-value
root:shoot 0.99 + 0.035 0.86 + 0.062 0.032 *
% primaryroots
21.59 + 1.90 14.18 + 2.95 0.022 *
Transgenics produce:
- more roots- more primary roots
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Localised
Rapid apparition of a dry zoneThe uptake region moves down quickly
- effect of the substrate and root density (?)
Uptake
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Uptake pictures
Superficial Deep
Identical behaviours for the differenttype of root systems
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Discussions
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Hypotheses on the influenceof the lack of aquaporins
On the development- roots less efficient if lacking AQP- increase of the root surface in order to balance the decrease
in efficiency:
- creation of new roots- increase in the growing rate of the existing roots (?)-
Functional equilibria (Brouwer 1963) Equilibrium between supply and demand
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increase of branchingincrease of branching
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In case of water stress- roots in the dry zone produce ABA- stomatal closure and decrease of transpiration
If uptake localised- faster response of the roots
Negative feed-back
Prevent a drying of the rhizosphere
Same dynamics observed in Partial RootZone Drying experiments (PRZD)
Hypotheses on transpirationand water uptake
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Conclusions
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Conclusions
The lack of aquaporins may have an influence on thedevelopmental processes (to be confirmed)
The localised dynamics of the water uptake
induces a tight regulation of the global uptake behaviour
Light transmission imaging allows theobservation of the water uptake in situ and without heavy
equipment
Functional-structural plant modelling could bea useful tool for the understanding of the water dynamics
in plant
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Acknowledgements
UCL:
Xavier DrayeMathieu JavauxFranois Chaumont
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INRA, Avignon:
Loc PagsClaude Doussan
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Thanks for your attention