title: Hydraulic conductance and mercury-sensitive water transport for roots of Opuntia acanthocarpa in relation to soil drying and rewetting.
abstract: 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 microM), which is known to block membrane water-transport channels (aquaporins), decreased LP and the radial hydraulic conductance for the stele (L(R, S)) of the distal root region by 32% and 41%, respectively; both LP and L(R, 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 L(R, S) by 41%. Under dry conditions, neither LP nor L(R, S) of the two root regions was inhibited by HgCl2. After 8 d of rewetting, HgCl2 decreased LP and L(R, S) of the distal region by 23% and 32%, respectively, but LP and L(R, 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 L(R, S) during drought and after rewetting. Thus, aquaporins are important for regulating water movement for roots of O. acanthocarpa.
authors.affiliation: Department of Organismic Biology, Ecology, and Evolution, University of California, Los Angeles, California 90095-1606, USA.
authors.forename: P
authors.initials: P
authors.lastname: Martre
authors.forename: G B
authors.initials: GB
authors.lastname: North
authors.forename: P S
authors.initials: PS
authors.lastname: Nobel
mesh_terms: D020346:Aquaporins / Q000378:metabolism; D019684:Magnoliopsida / Q000378:metabolism*; D008627:Mercuric Chloride / Q000494:pharmacology*; D018517:Plant Roots / Q000033:anatomy & histology / Q000187:drug effects / Q000378:metabolism*; D012987:Soil; D014867:Water / Q000378:metabolism*
chemical_list: D020346:Aquaporins; D012987:Soil; D014867:Water; D008627:Mercuric Chloride