Physiological and genetic analysis of water transport in the Arabidopsis root

CHRISTOPHE MAUREL, HÉLÈNE JAVOT, VIRGINIE LAUVERGEAT, JULIAN HEYES, MOIRA SUTKA, COLETTE TOURNAIRE

Buenos Aires, Argentina

Congreso; XIV International Biophysics Congress; 2002

SAB

The PIP subfamily encodes water channel proteins named aquaporins 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. 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 including PIP2;2 and PIP2;3 were isolated. The PIP2;2 and PIP2;3 aquaporins are close homologues with 96% identity and are both expressed in roots. 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 but was unchanged in a PIP2;3 mutant. The former mutants also showed a 10% increase in the osmolarity of sap exsudated 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 PIP aquaporins to root water uptake and show how very close aquaporin homologues have evolved with specific functions.