Aspen Bibliography


Mercuric chloride effects on root water transport in aspen seedlings

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Plant Physiology





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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 re- duced the activation energy of water transport in the roots from 10.82 􏰃 0.700 kcal mol􏰂1 to 6.67 􏰃 0.193 kcal mol􏰂1 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 se- verely reduced stomatal conductance in intact plants, and this reduction was partly reversed by 50 mM mercaptoethanol. In ex- cised 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.