Significance of oxygen transport through aquaporins.

Aquaporins are membrane integral proteins responsible for the transmembrane transport of water and other small neutral molecules. Despite their well-acknowledged importance in water transport, their significance in gas transport processes remains unclear. Growing evidence points to the involvement of plant aquaporins in CO delivery for photosynthesis. The role of these channel proteins in the transport of O and other gases may also be more important than previously envisioned. In this study, we examined O permeability of various human, plant, and fungal aquaporins by co-expressing heterologous aquaporin and myoglobin in yeast. Two of the most promising O-transporters (Homo sapiens AQP1 and Nicotiana tabacum PIP1;3) were confirmed to facilitate O transport in the spectrophotometric assay using yeast protoplasts. The over-expression of NtPIP1;3 in yeasts significantly increased their O uptake rates in suspension culture. In N. tabacum roots subjected to hypoxic hydroponic conditions, the transcript levels of the O-transporting aquaporin NtPIP1;3 significantly increased after the seven-day hypoxia treatment, which was accompanied by the increase of ATP levels in the apical root segments. Our results suggest that the functional significance of aquaporin-mediated O transport and the possibility of controlling the rate of transmembrane O transport should be further explored.