Effects of HgCl2 on principal parameters of exudation from maize detached root system

Abstract

To elucidate the role of aquaporins in the control of the root pressure, we tested the effects of HgCl2 (aquaporin blocker) at concentrations from 10−8 to 10−2 M on the exudation rate (J w). Experiments were performed with detached roots of 5–7-day-old etiolated maize (Zea mays L.) seedlings. HgCl2 suppressed exudation by 50–70% at the concentration of 2 × 10−5 M. At the concentration of 2.5 × 10−4 M, HgCl2 reduced J w during first 20–40 min, but in 2 h, it activated exudation by ten and more times. In this case, the root and osmotic pressures of the exudates increased by 1.5 times. The hydraulic conductance reduced approximately by 30% during first 30 min and increased severalfold in 2 h. The temperature coefficient (Q10) of J w attained 14 in 2 h. At the concentration of 10−2 M, HgCl2-induced acceleration of exudation was replaced by its inhibition essentially immediately. We suggested that a driving force for HgCl2-induced stimulation of the J w might be an increase in the osmotic component of the root pressure or the involvement of its nonosmotic (so-called metabolic) component. The results allow a supposition that aquaporins are involved in the control of water transport in the root.