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Plant Physiol, November 1999, Vol. 121, pp. 939-946
Mercuric Chloride Effects on Root Water Transport in Aspen
Seedlings1
Xianchong
Wan and
Janusz J.
Zwiazek*
Department of Renewable Resources, University of Alberta, 4-42
Earth Sciences Building, Edmonton, Alberta, Canada T6G
2E3
HgCl2 (0.1 mM) reduced pressure-induced water flux and root hydraulic
conductivity in the roots of 1-year-old aspen (Populus tremuloides Michx.) seedlings by about 50%. The inhibition was reversed with 50 mM mercaptoethanol. Mercurial treatment
reduced the activation energy of water transport in the roots from
10.82 ± 0.700 kcal mol 1 to 6.67 ± 0.193 kcal
mol1 when measured over the 4°C to 25°C temperature
range. An increase in rhodamine B concentration in the xylem sap of
mercury-treated roots suggested a decrease in the symplastic transport
of water. However, the apoplastic pathway in both control and
mercury-treated roots constituted only a small fraction of the total
root water transport. Electrical conductivity and osmotic potentials of
the expressed xylem sap suggested that 0.1 mM
HgCl2 and temperature changes over the 4°C to 25°C
range did not induce cell membrane leakage. The 0.1 mM
HgCl2 solution applied as a root drench severely reduced
stomatal conductance in intact plants, and this reduction was partly
reversed by 50 mM mercaptoethanol. In excised shoots, 0.1 mM HgCl2 did not affect stomatal conductance,
suggesting that the signal that triggered stomatal closure originated
in the roots. We suggest that mercury-sensitive processes in aspen
roots play a significant role in regulating plant water balance by
their effects on root hydraulic conductivity.
1
This study was funded by research grants from
the Natural Sciences and Engineering Research Council of Canada and
Sustainable Forest Management Network of Centres of Excellence.
*
Corresponding author; e-mail janusz.zwiazek{at}ualberta.ca; fax
780-492-1767.
© 1999 American Society of Plant Physiologists
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