PIP1 plasma membrane aquaporins in tobacco: from cellular effects to function in plants.

The molecular function of several aquaporins is well characterized, e.g. by analysis of aquaporin-expressing Xenopus oocytes. However, their significance in the physiology of water transport of multicellular organism is still uncertain in many cases. The tobacco plasma membrane aquaporin NtAQP1 was used to elucidate this issue. By comparing antisense plants which were inhibited in NtAQP1-expression to control plants. we found evidence for NtAQP1-function in cellular-and whole plant water-relations- Consequences of a decrease in cellular water permeability were determined by measurement of transpiration rate, stem and leaf water potential as well as growth experiments under extreme soil water depletion. Plants impaired in NtAQP1-expression showed a reduced root hydraulic conductivity and a lower water-stress resistance. In conclusion, the results give emphasis to the importance of a symplastic aquaporin-mediated water transport in whole plant water-relations.