Light and temperature induced variable leaf symplasmic hydraulic conductances in Juglans regia L. Are aquaporins involved? H Cochard1, S Sakr1, A Nardini2 [e-mail] 1 UMR PIAF, INRA France 2 Trieste University, Italy

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Light and temperature induced variable leaf
symplasmic hydraulic conductances in Juglans
regia L.Are aquaporins involved? H Cochard1, S
Sakr1, A Nardini2cochard_at_clermont.inra.fr1 UMR
PIAF, INRA France 2 Trieste University, Italy
                        XVII International Botanical Congress Vienna, Austria Center , 17 - 23 July 2005
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Understanding water pathways in leaves
Apoplasmic
Symplasmic
Gaseous
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Understanding water pathways in leaves
?
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Why should symplasmic resistances be variable?
Because water molecules cross cell membranes
through a Nobel prize winning molecule
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Recent evidences for variable leaf hydraulic
resistances
Sack et al (2002) light decreases leaf
hydraulic resistance
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Objectives of this study

• Confirm the light response Kleaf for walnut
• Confirm that stomatal movement was not involved
• Effect of light intensity
• Effect of temperature
• Molecular evidences for the implication of
  aquaporins in this light response

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Experimental Setup
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Experimental Setup
Kleaf Flow/LA / Pressure mmol s-1 MPa-1 m-2
Air pressure
Temp Bath
F2
air
F1
XYLEM
P
tap
1400 µmol m-2 s-1
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A typical experiment
Pressure
Temperature
400
Leaf conductance
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Can stomatal movement be responsible?
Leaves are infiltrated with water The hydraulic
conductance of the stomatal pore is also measured
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Can stomatal movement be responsible?
NO!
Light
Dark
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Effect of light intensity on leaf hydraulic
conductance
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Effect of bath temperature on leaf conductance
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Effect of bath temperature on leaf conductance
Light response of Kleaf is strongly temperature
dependant Not explained by water fluidity under
light conditions
Behavior of a biological membrane Implication of
aquaporins
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PIP Aquaporins in Walnut
flowers
Bud
xylem
leaf
root
Bark
F
M
ND
D
JrPIP2-1
JrPIP2-2
ARNr
Sakr et al Plant Phys 2003
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JrPIP2 Aquaporins is a water channel
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Do JrPIP2 transcripts accumulate with light ?
YES
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Can the gating of aquaporins alter leaf
conductance?
HgCl2 (200 µM) known to inhibit (some)
aquaporins among other proteins!
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Can the gating of aquaporins alter leaf
conductance?
DMSO dimethyl sulfoxide. Many effects,
aquaporin inhibitor?
Strong and rapidly reversed inhibition of leaf
conductance (minutes)
Osmotic effect? Effect on membrane polarity?
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Does leaf light response is caused by the
activation or by the traduction (synthesis) of
proteins ?
CHX (cycloheximide) inhibits protein traduction
in eukaryots
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Does leaf light response is caused by the
activation or by the traduction (synthesis) of
proteins ?
The light response is reversed in less than 1
hour with CHX
The synthesis of at least one protein is required
for the light response This protein has a
relatively high turnover
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Conclusions
Leaf hydraulic resistance is strongly light and
temperature dependant Variables leaf resistances
are located in the symplasmic pathway Proteins
(aquaporins) are involved in these responses The
synthesis or the activation of these proteins
seems finely regulated according to leaf
microclimate
WHY ?
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Understanding water relations in leaves
Leaf transpiration
Does variable symplasmic resistances buffer leaf
water status and favor stomatal function ?
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Light and temperature induced variable leaf
symplasmic hydraulic conductances in Juglans
regia L.Are aquaporins involved? H Cochard1, S
Sakr1, A Nardini2cochard_at_clermont.inra.fr1 UMR
PIAF, INRA France 2 Trieste University, Italy
                        XVII International Botanical Congress Vienna, Austria Center , 17 - 23 July 2005