Overexpression of a lily PIP1 gene in tobacco increased the osmotic water permeability of leaf cells

Membrane intrinsic proteins (MIP) facilitate the osmotic water transport across biomembranes and are involved in the transcellular and intracellular water flow in plants. An aquaporin-like gene, AqpL1, was isolated from lily flower using reverse transcriptase-polymerase chain reaction. Phylogenetic analysis showed that AqpL1 was a member of PIP1 subfamily. The results of northern hybridization indicated AqpL1 expressed in the whole plant but most strongly in young petal. Its expression decreased remarkably with flower age. AqpL1 gene could be properly expressed by in vitro translation and showed a 26 kDa monomer band revealed by autoradiography. Injection of AqpL1 cRNA into Xenopus oocytes resulted in an increase of the osmotic water permeability (P-f = 0.72 x 10(-2) +/- 0.05 cm s(-1)) for about 2-3 times compared to that (P-f = 0.24 x 10(-2) +/- 0.07 cm s(-1)) of the cells injected with water. Overexpression of AqpL1 in tobacco could greatly increase osmotic water permeability of leaf protoplasts (P-os-WT : P-os-L1 = 0.7 x 10(-1) cm s(-1) : 4.3 x 10(-1) cm s(-1)) and water conductivity of leaf cells (RWL-WT : RWL-L1 = 3.3% : 13.2%). It is concluded that AqpL1 is a water channel gene. However, it demonstrated much higher osmotic water permeability in tobacco cells than in oocytes. These results are consistent with the notion that AqpL1 is involved in regulating water and/or other solutes transport across the plant cell membrane.