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

Abstract

The short-term effects of sodium azide (NaN3) on water flow in red-osier dogwood (Cornus stolonifera Michx.) seedlings were examined in excised roots at a constant pressure of 0.3 MPa. NaN3 significantly decreased root water flow rates (Qv). 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 NaN3-induced decreases in Qv. Mercuric chloride (HgCl2) was also used to characterize the water flow responses and respiration of dogwood roots. Similarly to NaN3, 0.1 and 0.3 mM HgCl2 decreased root respiration rates and Qv. The lower, 0.05 mM HgCl2 treatment, reduced Qv, but had no significant effect on root oxygen uptake. The reduction of Qv in HgCl2-treated plants was only partly reversed by 50 mM mercaptoethanol. The mercurial inhibition of Qv suggested the presence of Hg-sensitive water channels in dogwood roots. The results indicate that root-absorbed NaN3 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.