The action of aquaporins in cell elongation, salt stress and photosynthesis

Abstract

Aquaporin belongs to a highly conserved group of membrane proteins called major intrinsic proteins (MIPs) that facilitate water transport across biological membranes. Aquaporins are membrane water channels that play critical roles in controlling the water content of cells and tissues. We focused on GhPIP1;2 which belongs to the PIP subfamily and GhgammaTIP1 which belongs to the gammaTIP group of the TIP subfamily. Northern blot analysis with gene-specific probes and real-time PCR demonstrated that GhPIP1;2 and GhgammaTIP1 are predominantly expressed during cotton fiber elongation, with the highest expression levels at 5 days post anthesis. The high and preferential expression of GhPIP1;2 and GhgammaTIP1 suggests that they may play important roles in supporting the rapid influx of water into vacuoles during cotton fiber cell expansion. Also, the effects of Ca2+ on aquaporins in salinity-stressed plants were studied. Researchers treated the protoplasts and plasma membrane with NaCl or CaCl2, alone or in combination. Under saline conditions, osmotic water permeability (Pf) values decreased in protoplasts and plasma membrane vesicles, and the same reduction was observed in the PIP1 aquaporin abundance, indicating inhibitory effects of NaCl on aquaporin functionality and protein abundance. Two different actions of Ca2+ were observed. Increase in free cytosolic calcium concentrations associated with stress perception may lead to aquaporin closure, however, the extra-calcium would lead to an upregulation of aquaporins. Meanwhile, experiments have demonstrated HvPIP2;1, one of barley aquaporins, has a higher water and CO2 transport activity. The goal of our plant aquaporin research is to determine the key aquaporin species responsible for water and CO2 transport, and to improve plant water relations, stress tolerance, CO2 uptake or assimilation, and plant productivity.