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Plant Physiol, May 2001, Vol. 126, pp. 352-362
Hydraulic Conductance and Mercury-Sensitive Water Transport for
Roots of Opuntia acanthocarpa in Relation to Soil
Drying and Rewetting1
Pierre
Martre,
Gretchen B.
North, and
Park S.
Nobel*
Department of Organismic Biology, Ecology, and Evolution,
University of California, Los Angeles, California 90095-1606 (P.M.,
P.S.N.); and Department of Biology, Occidental College, Los Angeles,
California 90041 (G.B.N.)
Drought-induced changes in root hydraulic conductance
(LP) and mercury-sensitive water transport
were examined for distal (immature) and mid-root (mature) regions of
Opuntia acanthocarpa. During 45 d of soil drying,
LP decreased by about 67% for distal and
mid-root regions. After 8 d in rewetted soil,
LP recovered to 60% of its initial value
for both regions. Axial xylem hydraulic conductivity was only a minor
limiter of LP. Under wet conditions, HgCl2 (50 µM), which is known to block
membrane water-transport channels (aquaporins), decreased
LP and the radial hydraulic conductance for
the stele (LR, S) of the distal root region
by 32% and 41%, respectively; both LP and
LR, S recovered fully after transfer to
2-mercaptoethanol (10 mM). In contrast,
HgCl2 did not inhibit LP of the
mid-root region under wet conditions, although it reduced LR, S by 41%. Under dry conditions, neither
LP nor LR, S of
the two root regions was inhibited by HgCl2. After 8 d
of rewetting, HgCl2 decreased LP
and LR, S of the distal region by 23% and
32%, respectively, but LP and
LR, S of the mid-root region were unaltered. Changes in putative aquaporin activity accounted for about 38% of the
reduction in LP in drying soil and for 61%
of its recovery for the distal region 8 d after rewetting. In the
stele, changes in aquaporin activity accounted for about 74% of the
variable LR, S during drought and after
rewetting. Thus, aquaporins are important for regulating water movement
for roots of O. acanthocarpa.
1
This work was supported by the National Science
Foundation (grant no. IBN-9975163).
*
Corresponding author; e-mail psnobel{at}biology.ucla.edu; fax
310-206-3987.
© 2001 American Society of Plant Physiologists
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