Effect of temperature on water transport through aquaporins

The mean effective water self-diffusion coefficient in maize root segments under the effect of aquaporin blocker (mercuric chloride, 0.1 mM) was measured using the spin-echo NMR method with pulsed magnetic field gradient within the temperature range from 10 to 35 A degrees C. HgCl2 caused the reduction in water diffusion by 30 % as compared to the control samples. Temperature dependences of water self-diffusion coefficients showed two linear regions with different values of Q(10) and activation energy, E-a. As the temperature reduced from 20 to 10 A degrees C, E-a values calculated from the Arrhenius plots were close to those of bulk water (20 +/- 3 kJ mol(-1)) and slightly changed for the sample pretreated HgCl2. Within the temperature range from 25 to 35 A degrees C the slope of temperature dependences became steeper and E-a values were 31 +/- 3 kJ mol(-1) for the control and 40 +/- 4 kJ mol(-1) for the treated sample. In the vicinity of 20 A degrees C, the temperature dependence of water diffusion via the mercury-sensitive water channels showed extreme value. In the region, the specific area of the mercury-sensitive aquaporins was 0.004 % of the total cell surface area. The data indicate that water transfer via aquaporins is sensitive to temperature, and the contributions of the transmembrane pathways (aquaporins, lipid bilayer) differ in different temperature ranges.