Water Stress Inhibits Hydraulic Conductance and
Leaf Growth
in Rice Seedlings but Not the
Transport of Water via
Mercury-Sensitive
Water Channels in the Root1
Zhongjin Lu and
Peter M. Neumann*
Plant Physiology Laboratory, Lowdermilk Faculty of Agricultural
Engineering, Technion Israel Institute of Technology, Haifa 32000, Israel
The mechanisms by which moderate
water stress (adding polyethylene glycol 6000 to the root medium)
induces a sustained inhibition of growth in emerging first leaves of
intact rice (Oryza sativa) seedlings was investigated
under growth-chamber conditions. Early (24 h) inhibition of leaf growth
was not related to changes in root size or in osmotic potential
gradients and cell wall-yielding characteristics in the leaf-expansion
zone of stressed seedlings. However, reductions in root-to-leaf
hydraulic conductance (L) were measured in two rice
cultivars after 4 or 24 h at various levels of water stress, and
these reductions correlated well with the inhibition of leaf growth. We
assayed L by a psychrometric method and, in intact
seedlings, by a novel osmotic-jump method. The addition of 0.5 mM HgCl2 to the root medium to inhibit water transport through Hg-sensitive water channels in the roots did not
inhibit leaf growth in unstressed seedlings. However, both leaf growth
and L were additionally reduced (by 49% and 43%,
respectively) within minutes of adding HgCl2 to roots of
water-stressed seedlings. Water stress therefore appeared to increase
the transport of water via Hg-sensitive water channels. Other
mechanisms were apparently involved in inhibiting overall
L and leaf growth.
1
This work was supported in part by the fund for
the promotion of research at Technion.
*
Corresponding author; e-mail agpetern{at}tx.technion.ac.il; fax
972-4-822-1529.
Plant Physiol. (1999) 120: 143-152
Copyright Clearance Center: 0032-0889/99/120//10
© 1999 American Society of Plant Physiologists
