Effect of Abscisic Acid on Root Hydraulic Conductivity

Markhart, Albert H.; Fiscus, Edwin L.; Naylor, Aubrey W.; Kramer, Paul J.

doi:10.1104/pp.64.4.611

Cited by 93 publications

(49 citation statements)

References 21 publications

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“…The observed decrease in exudation rate due to ABA treatment is consistent with previously published reports and related to a decrease in the hydraulic conductance due to the ABA treatment (5,13 The appearance of ABA in the root exudate demonstrates that considerable quantities of the hormone will be carried by the transpiration stream to the shoot if ABA is added to the irrigation water. During the 6 h required for steady-state exudate ABA levels to be achieved, a volume of exudate 8 to 12 times the volume of the root system has been forced through the root system.…”

Section: Discussionsupporting

confidence: 80%

“…Exogenously applied as well as endogenously produced ABA hardened plants to exposure to low temperatures (18,19). ABA is known to cause stomatal closure (16,20) and has been reported to alter root permeability to water (5,(7)(8)(9)13). In experiments where ABA is added to the irrigation water (18), it is often unclear whether the hormone acts on the root or is transported to the shoot and directly effects the stomata.…”

Section: Introductionmentioning

confidence: 99%

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Penetration of Soybean Root Systems by Abscisic Acid Isomers

Markhart¹

1982

Plant Physiol.

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The penetration of soybean (Glycine max L. cv. Ransom) root systems by exogenously applied isomers of abscisic acid was monitored by measuring the concentration of the chemical in the xylem exudate of root systems exposed to a three bar hydrostatic pressure difference. The cis-trans isomer penetrated more readily than the trans-trans isomer, however, up to 6 hours was needed to reach steady-state values. Exogenous abscisic acid also decreased volume flux through the root system and increased total carbon dioxide efflux from the vessel containing the root system.Recent evidence indicates an important role of ABA2 in plant resistance to environmental stress (13, 19). Exogenously applied as well as endogenously produced ABA hardened plants to exposure to low temperatures (18,19). ABA is known to cause stomatal closure (16,20) and has been reported to alter root permeability to water (5,(7)(8)(9)13). In experiments where ABA is added to the irrigation water (18), it is often unclear whether the hormone acts on the root or is transported to the shoot and directly effects the stomata.Despite the potential importance of exogenously applied plant growth regulators, there is a paucity of information on the uptake and transport of hormones to sites of action. The experiments presented here investigate the penetration of soybean root systems by ABA geometric isomers. This information is essential to understanding the mechanism of action of ABA and to the future use of exogenous ABA to ameleorate plant damage due to environmental stress. Additionally, a convenient accurate method of general use for measuring the transport of these compounds through root systems is described. MATERIALS AND METHODSSoybean (Glycine max L. cv. Ransom) plants were grown hydroponically in 3-L plastic pots containing half-strength Hoagland solution for 20 to 40 days in controlled environment chambers at the Duke University Phytotron as described previously (14 Twenty 1d aliquots were analyzed directly with an Altex Model 310 high performance liquid chromatograph with a UV (254 nm) detector for the presence of ABA. Separation of the two geometric isomers was achieved with a solvent system of methanol:H20: acetic acid (40:60: 1), a LiChrosorb RP-18 column, and a flow rate of 1 ml/min. Standard curves of peak height versus concentration were linear between 10-6 and l0-4 M and were used to determine exudate ABA concentration. The ABA concentration of the ambient solution was also monitored during the experiment. The exudate ABA concentration expressed as a fraction of the ambient concentration was used as a relative measure of the penetration of the isomers.Exudation Rates. Exudation rates were measured as the volume of exudate flowing from the cut stem per unit time. Rates are expressed on a whole root basis.Respiration. Root respiration was monitored by measuring the CO2 concentration of the gas passing through the pressure vessel with an IR gas analyzer operated in the absolute mode. Rates were expressed as a percent of the rate at the time...

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Section: Discussionsupporting

confidence: 80%

Section: Introductionmentioning

confidence: 99%

Penetration of Soybean Root Systems by Abscisic Acid Isomers

Markhart¹

1982

Plant Physiol.

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“…This suggests that root water channels play an important role in regulating plant water relations. The pressure-flux curves in untreated controls and in HgCl 2 -treated roots were consistent with this theory (Fiscus, 1975) and previous observations (Lopushinsky, 1964;Markhart et al, 1979b;Jackson et al, 1996). The relationship between J v and applied pressure was highly linear in pressures above 0.15 MPa.…”

Section: Discussionsupporting

confidence: 77%

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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“…ABA is synthesized in the roots of several species and it has been hypothesized to be active in stomatal functioning (Davies et aL, 1987). In addition, Lp is affected by exogenous ABA levels (Markhart et al, 1979;Fiscus, 1981).…”

Section: Plant-growth Substancesmentioning

confidence: 99%

Root hydraulic conductivity and xylem sap levels of zeatin riboside and abscisic acid in ectomycorrhizal Douglas fir seedlings

1990

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SUMMARYMechanistic hypotheses to explain mycorrhizal enhancement of root hydraulic conductivity (Lp) suggest that phosphorus (P) nutrition, plant growth substances and/or altered morphology may be responsible. Such ideas are based on work with VA (vesicular-arbuscular) mycorrhizas. Since VA mycorrhizas and ectomycorrhizas differ m many respects, they may alter host plant water uptake via different mechanisms. This paper examines Lj, in various ectomycorrhizal associations while considering factors which are important to the VA mycorrhizal effect on Lp. Douglas fir Pseudotsuga menziesii (Mirb.) Franco] seedlings inoculated with the ectomycorrhizal fungi Laccaria bicolor (Maire) Orton and Hebeloma crustuliniforme (Bull, ex St. Amans) Quel. and non-inoculated seedlings infected naturally with Thelephora were grown under three low levels of P fertilization (1, 10 and 100/^M P). Seedling morphology, tissue P levels, Lp and plant growth substance levels in xylem sap were measured after nine months growth. Increased tissue P and decreased root/shoot ratio correlated with increased L^, in each of the mycorrhizal treatments. When adjusted for the effect of these two factors, Lp of Laccaria and Hebeloma seedlmgs was still lower than the Thelephora seedlings. In a subsequent experiment, the Lp of seedlings with Hebeloma and Rhizopogon vinicolor Smith mycorrhizas was compared to the Lp of non-mycorrhizal seedlings (grown at 100 mM P) and no differences were found among treatments. The lack of an ectomycorrhizal effect on Lp is quite different from the enhancement of host Lp by VA mycorrhizas. Zeatin riboside concentrations of Thelephora-and Hebeloma-infected seedlings were similar, yet higher than with Laccarta. There was no relationship between plant growth substances and Lp in ectomycorrhizal Douglas fir, despite lower zeatin riboside concentrations for Laccar/a-inoculated plants.

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Effect of Abscisic Acid on Root Hydraulic Conductivity

Cited by 93 publications

References 21 publications

Penetration of Soybean Root Systems by Abscisic Acid Isomers

Penetration of Soybean Root Systems by Abscisic Acid Isomers

Mercuric Chloride Effects on Root Water Transport in Aspen Seedlings

Root hydraulic conductivity and xylem sap levels of zeatin riboside and abscisic acid in ectomycorrhizal Douglas fir seedlings

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