Effects of Mercuric Chloride on the Hydraulic Conductivity of Tomato Root Systems (Evidence for a Channel-Mediated Water Pathway)

Maggio, Aurelio; Joly, Robert

doi:10.1104/pp.109.1.331

Cited by 208 publications

(154 citation statements)

References 23 publications

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“…This expression can be organ and tissue-specific with a pattern suggesting that aquaporins are involved in both cell expansion and vascular water permeability (H6fte et al, 1992;Jones and Mullet, 1995;Daniels et al, 1996). Water channels are assumed to largely contribute to hydraulic conductivity in Chara cells (Henzler and Steudle, 1995), Arabidopsis leaf protoplasts (Kaldenhoff et al, 1995), the tomato root system (Maggio and Joly, 1995), and sunflower hypocotyls (Hejnowicz and Sievers, 1996). Indeed, expression of some aquaporin genes was affected by osmotic stress, strengthening the hypothesis that they play a significant role in the control of water movement (Fray et al, 1994;Guerrero et al, 1990;Yamada et aL, 1995;Yamaguchi-Shinozaki et aL, 1992).…”

Section: Introductionmentioning

confidence: 89%

Two TIP‐like genes encoding aquaporins are expressed in sunflower guard cells

et al. 1997

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SummarySunTIP7 and SunTIP20 are closely related sunflower cDNAs showing a deduced amino acid sequence homologous to proteins of the tonoplast intrinsic protein (TIP) family. Their expression in Xenopus oocytes caused a marked increase in osmotic water permeability (demonstrating that they are water channels) which was sensitive to mercury. In leaves, in situ hybridization revealed that both SunTIP7 and SunTIP20 mRNA accumulated in the guard cells. The possible involvement of SunTIPs in stomatal movement was examined by comparing the time course of transcript accumulation and leaf conductance during the daily cycle and following a water limitation. SunTIP7 mRNA fluctuations fitted changes occurring in leaf conductance. The transcript levels were markedly and systematically increased during stomatal closure. It is suggested that aquaporin SunTIP7 facilitates water exit associated with a decrease in guard cell volume. In the same conditions, the transcript level of SunTIP20 remained constant indicating that SunTIP genes are differentially regulated within the same cell.

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Section: Introductionmentioning

confidence: 89%

Two TIP‐like genes encoding aquaporins are expressed in sunflower guard cells

et al. 1997

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“…Mercury reversibly inhibits the bulk water transport across membranes in animal cells (Pratz et al, 1986;Meyer and Verkman, 1987) and plant cells (Maggio and Joly, 1995;Carvajal et al, 1996;Maurel et al, 1997;Niemietz and Tyerman, 1997). This reversible inhibition is used to demonstrate the existence of proteinaceous water channels (Chrispeels and Maurel, 1994).…”

Section: Discussionmentioning

confidence: 99%

“…This closure inhibits water transport and increases E a to the level of that for transport through the lipid pathway (Macey, 1984). An inhibition of water transport by mercury was reported in cell membranes isolated from higher plants Niemietz and Tyerman, 1997) and in whole root systems (Maggio and Joly, 1995;Carvajal et al, 1996). However, the effects of mercury reagents on E a have not been investigated in intact higher plants.…”

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confidence: 99%

Mercuric Chloride Effects on Root Water Transport in Aspen Seedlings

1999

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HgCl 2 (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 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 mercurytreated 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 HgCl 2 and temperature changes over the 4°C to 25°C range did not induce cell membrane leakage. The 0.1 mM HgCl 2 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 HgCl 2 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.Several criteria have been used to infer the presence of water-transporting channels in cell membranes. These include a high ratio of osmotic to diffusional water permeability (P f /P d Ͼ1), low Arrhenius activation energy (E a Ͻ 6 kcal mol Ϫ1 ) for water transport, and its reversible inhibition by mercury sulfhydryl reagents (for reviews, see Chrispeels and Agre, 1994;Verkman et al., 1996;Maurel, 1997). The transport of water through the lipid bilayer has a high E a , usually above 10 kcal mol Ϫ1 (Macey, 1984). Water transport can also be via water channel proteins (aquaporins), which have been found in the tonoplasts (Maurel et al., 1993) and plasma membranes (Kammerloher et al., 1994) of plants. It is generally acknowledged that the transport of water via channels is less temperature dependent and has a lower E a (Ͻ 6 kcal mol Ϫ1 ) than transport via the lipid pathway (Finkelstein, 1987;Chrispeels and Agre, 1994). Water transport via aquaporins is characteristically inhibited by mercurial reagents, which react with sulfhydryl groups in the channel proteins and result in closure of the channels. This closure inhibits water transport and increases E a to the level of that for transport through the lipid pathway (Macey, 1984). An inhibition of water transport by mercury was reported in cell membranes isolated from higher plants Niemietz and Tyerman, 1997) and in whole root systems (Maggio and Joly, 1995;Carvajal et al., 1996). However, the effects of mercury reagents on E a have not been investigated in intact higher plants.Based on the composite transport model (Steudle and Frensch, 1996), water transport is via three parallel pathways, apoplastic, ...

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“…Although these experiments do not directly prove the point, it seems likely that the principal perturbation caused by Hg may have been through an effect on the radial movement of water across the root to the xylem, and that this path is proteinmediated. It has been shown that HgCl # blocks the flow of water through aquaporins in plant roots and that the flow can be restored by reducing agents (Maggio & Joly, 1995 ;Carvajal et al, 1996). Using DTT as a scavenger for Hg# + , the L !…”

Section: mentioning

confidence: 99%

Does calcium ameliorate the negative effect of NaCl on melon root water transport by regulating aquaporin activity?

2000

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The hydraulic conductance (L ! ) of detached, exuding root systems from melon (Cucumis melo cv. Amarillo oro) was measured. All plants received a half-strength Hoagland nutrient solution, and plants stressed either solely with NaCl (50 mM) or with NaCl (50 mM) following treatment (2 d) with CaCl # (10 mM) were compared with controls and CaCl # -treated (10 mM) plants. The L ! of NaCl-treated plants was markedly decreased when compared to control and CaCl # -treated plants, but the decrease was smaller when NaCl was added to plants previously treated with CaCl # . A similar effect was observed when the flux of Ca# + into the xylem and the Ca# + concentration in the plasma membrane of the root cells were determined. In control, CaCl # -and NaCljCaCl # -treated plants, HgCl # treatment (50 µM) caused a sharp decline in L ! to values similar to those of NaCl-stressed roots, but L ! was restored by treatment with 5 mM DTT. However, in NaCl roots only a slight effect of Hg# + and DTT were observed. The effect of all treatments on L ! was similar to that on osmotic water permeability (P f ) of individual protoplasts isolated from roots. The results suggest that NaCl decreased the passage of water through the membrane and roots by reducing the activity of Hg-sensitive water channels. The ameliorative effect of Ca# + on NaCl stress could be related to water-channel function.

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Effects of Mercuric Chloride on the Hydraulic Conductivity of Tomato Root Systems (Evidence for a Channel-Mediated Water Pathway)

Cited by 208 publications

References 23 publications

Two TIP‐like genes encoding aquaporins are expressed in sunflower guard cells

Two TIP‐like genes encoding aquaporins are expressed in sunflower guard cells

Mercuric Chloride Effects on Root Water Transport in Aspen Seedlings

Does calcium ameliorate the negative effect of NaCl on melon root water transport by regulating aquaporin activity?

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