Different cation stresses affect specifically osmotic root hydraulic conductance, involving aquaporins, ATPase and xylem loading of ions in Capsicum annuum, L. plants

In order to study the effect of nutrient stress on water uptake in pepper plants (Capsicum annuum L.), the excess or deficiency of the main cations involved in plant nutrition (K+, Mg2+, Ca2+) and two different degrees of salinity were related to the activity of plasma membrane H+-ATPase, the pH of the xylem sap, nutrient flux into the xylem (J(s)) and to a number of parameters related to water relations, such as root hydraulic conductance (L-0), stomatal. conductance (g(s)) and aquaporin activity. Excess of K+, Ca+ and NaCl produced a toxic effect on L-0 white Mg2+ starvation produced a positive effect, which was in agreement with aquaporin functionality, but not with ATPase activity. The xylem pH was altered only by Ca treatments. The results obtained with each treatment could suggest that detection of the quality of the nutrient supply being received by roots can be related to aquaporins functionality, but also that each cation stress triggers specific responses that have to be assessed individually. (C) 2006 Elsevier GmbH. All rights reserved.