The distribution of aquaporin subtypes (PIP1, PIP2 and gamma-TIP) is tissue dependent in soybean (Glycine max) root nodules.
BACKGROUND AND AIMS The inner cortical cells (IC-cells) of legume root nodules have been previously shown to regulate the resistance to nodule O2 diffusion by a rapid contraction/expansion mechanism, which controls the volume of intercellular spaces and their occlusion by a liquid phase. The expression of aquaporins in IC-cells was also found to be involved in this nodule O2 diffusion mechanism. The aim of this study was to compare the expression of plasma membrane intrinsic proteins (PIP) aquaporin isoforms with tonoplast intrinsic protein (gamma-TIP) in both IC-cells and adjacent cell types.


METHODS
Using immunogold labelling in ultra-thin sections of Glycine max nodules, the expression of two PIP isoforms was observed and compared with the gamma-TIP pattern.


RESULTS
The plasma membrane aquaporins PIP1 and PIP2 were expressed more in IC-cells and endodermis than in pericycle and infected cells. The tonoplast aquaporin gamma-TIP has shown a distribution pattern similar to that of the PIPs.


CONCLUSIONS
PIPs and gamma-TIP aquaporins are highly expressed in both plasmalemma and tonoplast of nodule IC-cells. This distribution is consistent with the putative role of water fluxes associated with the regulation of nodule conductance to O2 diffusion and the subsequent ATP-dependent nitrogenase activity. In the endodermis, these aquaporins might also be involved in nutrient transport between the infected zone and vascular traces.
Laboratoire de Physiologie et Biochimie Végétales, UMR 6161 CNRS, Université de Poitiers, France. pfleurat@univ-poitiers.fr
Pierrette
P
Fleurat-Lessard
Philippe
P
Michonneau
Masayoshi
M
Maeshima
Jean-Jacques
JJ
Drevon
Rachid
R
Serraj
D020346:Aquaporins / Q000378:metabolism*; D018506:Gene Expression Regulation, Plant / Q000502:physiology; D010940:Plant Proteins / Q000378:metabolism*; D018517:Plant Roots / Q000378:metabolism / Q000382:microbiology*; D013025:Glycine max / Q000378:metabolism* / Q000382:microbiology; D014018:Tissue Distribution; D014867:Water / Q000378:metabolism
D020346:Aquaporins; D010940:Plant Proteins; D014867:Water