Poster: Water relations

Abs # 160: Effects of root media pH on water transport in paper birch (Betula papyrifera) seedlings in relation to root temperature and abscisic acid treatments

Presenter:	Zwiazek, Janusz J., janusz.zwiazek@ualberta.ca
Authors	Zwiazek, Janusz J. (A)   Kamaluddin, Mohammed  (A)
Affiliations:	(A): University of Alberta

Exposure of birch (Betula papyrifera Marsh.) seedling roots to pH 4 and 8 significantly decreased root hydraulic conductivity (L_p) and stomatal conductance (g_s) compared with pH 6. When roots of solution culture-grown (pH 6) seedlings were transferred to pH 4 or 8, their steady-state water flow (Q_v) declined within minutes, followed by a decline in g_s. The root O₂ uptake rates were not significantly affected by the pH treatments. Treatment of roots with HgCl₂ at pH 6 resulted in a greater decrease of Q_v compared with pH 4 and 8. Lowering root temperature from 21^oC to 4^oC decreased Qv irrespective of media pH. Low root temperatures did not offset the effects of media pH 4 on Q_v and the roots in this treatment had high activation energy for water flow. Conversely, roots exposed to pH 8 showed low activation energy similar to that of pH 6. When 2 µM abscisic acid, [(±)-cis-trans-ABA], was added to the root medium, Q_v increased in roots that were incubated at the lower pH, but not at pH 8. This increase was temperature-dependent and occurred when the root temperature was 21^oC, but not 4^oC. We suggest that pH treatments are responsible for altering root water flow properties through their effects on the activity of water channels. These results support the concept that ABA effects on water channels are modulated by other, possibly metabolically- and pH-dependent factors.