Final Activity Report Summary - SALINITY AND AQUAPORINS (Molecular and biochemical responses to salinity. Functionality of aquaporins) In this project the identification and characterisation of different plasma membrane aquaporin proteins in different plants was carried out. The role of these proteins under stress conditions such as salinity has been established, comparing protein accumulation under different treatments. The correlation between protein level in the plasma membrane with water flows and hydraulic conductivities was determined in order to elucidate water relations. Since calcium has an important role in plant physiology involvement in the responses to stresses and controls numerous processes, the role of calcium in water transport to cell signalling and metabolism has been also studied. The ameliorative effect of Ca2+ on water transport and aquaporins status under salinity has been studied in different reports and several cultivars. It has been demonstrated that under saline conditions calcium concentration is reduced in the apoplast, into the cells and on plasma membrane of roots of pepper plants, and that the concentrations were increased or restored when extra calcium was added to the nutrient solution. It was also shown that nutritional calcium is involved in plasma membrane water channel regulation and a restoration of PIP content has been shown when extra Ca2+ was added to the nutrient solution in NaCl treated plants with regard the NaCl treatment. Thus, calcium seems to be involved in plasma membrane aquaporin regulation via a chain of processes within the cell or controlling the aquaporin abundance, but not by alteration of the stability of the plasma membrane. Two different effects of calcium has been demonstrated in plasma membrane vesicles and protoplasts isolated from roots of pepper plants under different saline treatments. 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 the inhibitory effect of NaCl on the aquaporin functionality and protein abundance. The cytosolic Ca2+ concentration, Ca2+cyt, was also reduced by salinity. Two different actions of Ca2+ were observed. On the one hand, it enhanced the activity of aquaporins in protoplasts under salt stress and, on the other hand, aquaporins in plasma membrane vesicles were blocked by external Ca2+, indicating that several combined mechanisms may work in the regulation of pepper root aquaporins under salt stress. Finally, the effect of the interaction NaCl- B on water transport has been determining water relations and aquaporins content. Our results suggested that under salt stress the activity of specific membrane components can be influenced directly by B, ameliorating the NaCl effects.
