Function and regulation of aquaporins in the Arabidopsis root

CHRISTOPHE MAUREL, HÉLÈNE JAVOT, VIRGINIE LAUVERGEAT, SHENG CHEN, MOIRA SUTKA, COLETTE TOURNAIRE AND VERONIQUE SANTONI.

Buenos Aires, Argentina

Simposio; Satellite Course and Symposia "Volume Regulation in Animal and Plant Cells"; 2002

Comite organizador ad hoc

The PIP subfamily encodes aquaporin water channels in the plasma membrane of plant cells and comprises 13 members in Arabidopsis thaliana. The hydraulic conductivity (Lp) of roots excised from Arabidopsis plants was measured in a pressurized chamber and was inhibited 50-70% by mercury, a general blocker of aquaporins. Previous observations in Arabidopsis suspension cells have revealed that both divalent cations and pH regulate plasma membrane water permeability through a membrane delimited switch from active to inactive water channels. Evidence for a control of root water channels by pH will be presented. The function of PIP aquaporins was also investigated by isolating knock-out mutants in Arabidopsis. For this, a library of plant lines mutagenized by insertion of Agrobacterium tumefaciens T-DNA was screened by PCR and six insertion mutants corresponding to four independent PIP genes were isolated. The PIP2;2 and PIP2;3 aquaporins are close homologues with 96% identity and are both expressed in roots, with a predominant expression in the cortex and in the stele. The Lp of root cortex cells, as measured by means of a cell pressure probe, was reduced by 25% in two independent PIP2;2 mutants. The former mutants also showed a 10% increase in the osmolarity of sap exuded from roots. This slight increase may reflect an increased solute pumping activity to compensate for a decreased root Lp. Altogether our data provide evidence for the contribution of a single aquaporin gene to root water uptake and show how very close aquaporin homologues have evolved with specific functions.