Metabolic inhibition of root water flow in red‐osier dogwood (Cornus stolonifera) seedlings

Abstract

The short-term effects of sodium azide (NaN(3)) on water flow in red-osier dogwood (Cornus stolonifera Michx.) seedlings were examined in excised roots at a constant pressure of 0.3 MPa. NaN(3) significantly decreased root water flow rates (Q(v)). It also induced a significant reduction in root respiration and reduced stomatal conductance to a greater extent in intact seedlings than in excised shoots. Apoplastic flow of water increased with the NaN(3)-induced decreases in Q(v). Mercuric chloride (HgCl(2)) was also used to characterize the water flow responses and respiration of dogwood roots. Similarly to NaN(3), 0.1 and 0.3 mM HgCl(2) decreased root respiration rates and Q(v). The lower, 0.05 mM HgCl(2) treatment, reduced Q(v), but had no significant effect on root oxygen uptake. The reduction of Q(v) in HgCl(2)-treated plants was only partly reversed by 50 mM mercaptoethanol. The mercurial inhibition of Q(v) suggested the presence of Hg-sensitive water channels in dogwood roots. The results indicate that root-absorbed NaN(3) metabolically inhibited water channel activities in roots and in shoots and resulted in stomatal closure. It is suggested that the inhibition of respiration that occurs in plants stressed with environmental factors such as flooding, cold soils, and drought may be responsible for the closure of water channels in root cells and inhibition of root water flow.

Ethylene Enhances Water Transport in Hypoxic Aspen

“…The presence of water channel proteins in the plasma membrane and the tonoplast allows a plant to regulate its water flow through the cell-tocell pathway (Chrispeels et al, 1997). Metabolic dependence of Q v and the effects of respiration on water channel function have been reported for different plants (Tyerman et al, 1999;Wan and Zwiazek, 1999;Zhang and Tyerman, 1999;Kamaluddin and Zwiazek, 2001;Wan et al, 2001). In wheat (Triti- cum aestivum) root cells, the extent of inhibition of cell hydraulic conductivity was similar in roots treated with HgCl 2 and hypoxia and interpreted as a result of the decreased phosphorylation of aquaporins (Zhang and Tyerman, 1999).…”

“…In wheat (Triti- cum aestivum) root cells, the extent of inhibition of cell hydraulic conductivity was similar in roots treated with HgCl 2 and hypoxia and interpreted as a result of the decreased phosphorylation of aquaporins (Zhang and Tyerman, 1999). NaN 3 , a potent inhibitor of oxidative phosphorylation, is also known to rapidly inhibit Q v across membranes (Kamaluddin and Zwiazek, 2001). Water transport through some aquaporins is regulated by phosphorylation (Daniels et al, 1994;Maurel et al, 1995;Johansson et al, 1998).…”

“…Aquaporins are located in root cell membranes (Chrispeels and Maurel, 1994) at a high density (Johansson et al, 1998). In our previous work (Wan andZwiazek, 1999, 2001;Kamaluddin and Zwiazek, 2001), we showed that the root water channels in aspen (Populus tremuloides) and Cornus stolonifera rapidly responded to changes in root metabolism. Phosphorylation of the aquaporins has been suggested to be the likely mechanism controlling water permeation through the cell membranes (Maurel, 1997;Johansson et al, 1998).…”

“…The steady-state root flow rate (Q v ) was measured following the hydrostatic pressure method (Wan and Zwiazek, 1999; Kamaluddin and Zwiazek, 2001). A 0.25-L glass cuvette containing one-half-strength Hoagland solution was inserted into a pressure chamber (PMS Instruments).…”

SWAP version 4

“…Kamaluddin and Zwiazek (2001) demonstrated, by inhibition of the metabolism of the roots, that a positive correlation between root respiration and water uptake exists. This implies a gradual decrease of root water uptake with increased oxygen stress (Bartholomeus et al 2008).…”