Kinetic analyses of plant water relocation using deuterium as tracer – reduced water flux of Arabidopsis pip2 aquaporin knockout mutants.

Due to reduced evaporation and diffusion of water molecules containing heavier isotopes, leaf water possesses an elevated ¹⁸O or ²H steady-state content. This enrichment has been exploited in plant physiology and ecology to assess transpiration and leaf water relations. In contrast to these studies, in this work the ²H content of the medium of hydroponically grown Arabidopsis thaliana was artificially raised, and the kinetics of ²H increase in the aerial parts recorded during a short phase of 6–8 h, until a new equilibrium at a higher level was reached. A basic version of the enrichment models was modified to establish an equation that could be fitted to measured leaf ²H content during uptake kinetics. The fitting parameters allowed estimation of the relative water flux q _leaf into the Arabidopsis rosette. This approach is quasi-non-invasive, since plants are not manipulated during the uptake process, and therefore, offers a new tool for integrated analysis of plant water relations. The deuterium tracer method was employed to assess water relocation in Arabidopsis pip2;1 and pip2;2 aquaporin knockout plants. In both cases, q _leaf was significantly reduced by about 20%. The organ and cellular expression patterns of both genes imply that changes in root hydraulic conductivity, as previously demonstrated for pip2;2 mutants, and leaf water uptake and distribution contributed in an integrated fashion to this reduced flux in intact plants. [ABSTRACT FROM AUTHOR]