Water transport in sunflower root systems: effects of ABA, Ca2+ status and HgCl2

Abstract

Excised 20-d-old sunflower roots (Helianthus annuus L. cv. Sun-Gro 380) with different Ca2+ status were used to study the effects of root Ca2+ status and abscisic acid (ABA) on the exudation rate (Jv), the hydraulic conductivity of the root (Lpr), the flux of exuded Ca2+ (JCa), and the gradient of rosmotic pressure between the xylem and the external medium. Jv and Lpr increased in direct proportion to the Ca2+ status of the root. Addition of ABA (4 µM) at the onset of exudation in the external medium made Jv and Lpr rise, and this effect also increased with the Ca2+ status. The effects of HgCl2 and its interaction with ABA on water transport in the root were also studied. Addition of HgCl2 (1 µM) 2 h after the onset of exudation in the external medium quickly inhibited Jv, independently of the presence of ABA in the root medium. The results recorded here point to the involvement of ABA and Ca2+ in the regulation of root water flow, as well as the existence of aquaporins in the cell membranes of sunflower roots.