NtPIP1;1 and NtPIP2;1 Aquaporins have Different Localization in Nicotiana tabacum Cells

Movement of water across cellular membranes is facilitated by the presence of water channels named aquaporins. Plant plasma membrane intrinsic proteins (PIPs) fall into two groups, PIP1s and PIP2s that exhibit different water channel activities. So PIP1s are inactive, whereas PIP2s induce a marked increase in the membrane osmotic water permeability coefficient, Pf. This difference may be due to their subcellular localization. The aim of this research was to determine the subcellular localization of NtPIP1;1 and NtPIP2;1 in living tobacco cells. In this experimental study, NtPIPs cDNA sequences were fused to green fluorescent protein gene and expressed transiently in tobacco mesophyll protoplasts. Then, cellular localization of aquaporins was investigated using fluorescent microscope under blue excitation wavelength. When expressed alone, NtPIP1;1 fusion protein was retained in the internal membrane structures, whereas NtPIP2;1 was found in membrane structure within the cell. To identify the internal structures containing NtPIP1;1 fusion proteins, NtPIP1;1-GFP was co-expressed in tobacco protoplasts with the YFP::HDEL protein, an ER marker. As shown, NtPIP1;1-GFP and YFP::HDEL colocalized. NtPIP2;1 was transported to plasma membrane, but NtPIP1 was retained in the ER of tobacco protoplasts so showed no water transport activity.