The Kinetics of Chloride Accumulation and Transport in Exuding Roots

Hodges, Thomas K.; Vaadia, Yoash

doi:10.1104/pp.39.3.490

Cited by 12 publications

(5 citation statements)

References 16 publications

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“…Furthermore, transport was highly sensitive to the metabolic inhibitor, DNP. These results concur with those found by other investigators for radial Cl transport in onion (14) and corn (21) …”

Section: Resultssupporting

confidence: 82%

Radial Transport of Sodium and Chloride into Tomato Root Xylem

Maas

Ogata

1972

Plant Physiol.

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Transport of Na and Cl across exuding tomato (Lycopersicon esculentum Mill.) roots was determined as a function of ambient NaCl concentrations in the ranges of both systems 1 and 2.Kinetics of radial transport under steady-state conditions and the effect of dinitrophenol indicate that Na and Cl were transported by two (5,16,17,19,24,30,34,37). Both the root and the stem have been implicated in the regulation of Na transport to the leaves. Basically, the proposed mechanisms of root regulation involve discriminatory exclusion of Na at the plasmalemma (10, 13, 20), Na-selective absorption into the vacuole by the tonoplast (18) and possibly, active Na extrusion from the cortical cells across the plasmalemma (1 1, 18, 28, 29, 31). Further Na dilution may occur in the stem where Na is selectively withdrawn from the xylem stream by adjacent living cells (1,16,17,30,34,36) and either sequestered there or retranslocated by way of the phloem to the root (5,23).Directly related to the mechanism of exclusion, and perhaps differing only by degree, is the mechanism whereby accumulator plants translocate Na or Cl readily to the shoots. Recently, the concept of an active anion pump as the driving force for cation transport to the xylem has received increasing support (2-4, 12, 26, 27, 35). The rationale for this theory is based primarily on the interpretation of electrochemical potentials 64 measured across exuding roots. However, the interpretations are not unequivocally accepted (18,32,33), and the mechanism of Na and Cl transport to the xylem remains in doubt.The purpose of the present investigation was to test further the active anion pump concept of salt transport with a plant that readily transports Na and Cl to the shoot. The tomato plant was chosen because it meets this criterion and because the transport of Na by this plant has been reported to be metabolically facilitated (15). The role of metabolism and steady-state kinetics of radial transport were determined over a broad range of ambient NaCl concentrations. MATERIALS AND METHODSPlant Culture. Decapitated root systems from 23-day-old tomato (Lycopersicon esculentum Mill. cv. Heinz 1350) plants were used as the experimental material. Plants were grown from seed germinated between moist paper towels suspended over tenth-strength Hoagland's solution. Seedlings were transferred when 5 cm high to 14-liter polyethylene containers of half-strength Hoagland's solution. Phosphate was reduced to 0.25 mm and Fe was added as the metal chelate of diethylenetriamine pentaacetate. Culture solutions were prepared from demineralized water and reagent-grade salts. Eight plants per container were supported in holes in Styrofoam' covers with strips of polyurethane foam wrapped around the stem. The plants were grown in environmental chambers at 25 C and with a 16-hr photoperiod at 3300 ft-c light intensity. Solutions were aerated continuously and the pH was maintained between 6.0 and 6.5 with HNO.Experimental Procedure. All plants were transferred to 1 meq/1 CaSO4 solutions (pH 6) f...

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Section: Resultssupporting

confidence: 82%

Radial Transport of Sodium and Chloride into Tomato Root Xylem

Maas

Ogata

1972

Plant Physiol.

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“…These (18,22). A passive transport to the xylem in the high concentration range is supported by others, notably Hodges and Vaadia (12) with onion roots and Minchin and Baker (24, 25) with castor bean. Liiuchli and Epstein (20), however, concluded that lateral transport of Clacross corn roots is mediated by dual mechanisms of ion absorption which they believe to reside in the plasmalemma.…”

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confidence: 53%

Accumulation and Radial Transport of Ions from Potassium Salts by Cucumber Roots

Cooil¹

1974

Plant Physiol.

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Accumulation of K+ is insensitive to the anion supplied with it at a solution concentration below 1 mM. Rates of K+ transport to the xylem from the same solutions are, however, dependent upon the anion present and decrease in the order NO3->> Cl-> SOI2-. Parallel effects on rates of exudation and anion transport result from kind and concentration of anion supplied and time of exposure to the solution. When high K salt concentrations are used, only linear relationships are found between solution concentrations and transport rates. However, ion concentration in the exudate increases more than external solution concentration, while exudation rate is unaffected. It is suggested that some of the ions transported are from compartments within the cells. At high solution concentrations KNO3 results in more exudation and in higher ion concentration in the exudate than is found with KCI.The processes involved in transport of ions from the external medium into the xylem of roots continue to evoke controversy and have been discussed in several recent reviews (1,18,19,27). Liittge and Laties (22) Cucumber roots can be induced to exude from the xylem profusely. These roots reduce little of the NO3-that is absorbed, and most of it is transported to the stems and leaves (3). As with tobacco (30, 31), cucumber roots depleted of NO3-respond to a new supply of this ion with increased rates of exudation and salt transport. These properties make the cucumber root ideal for studying ion transport to the xylem.This report compares patterns of accumulation and radial transport in cucumber roots of K salt ions supplied at concentrations below 1 mm, and transport at concentrations of 0.5 to 10 mM. MATERIALS AND METHODSPlant Culture. Seeds of Cucumnis sativus L. cv. Burpeeana Hybrid were soaked in deionized water with continuous aeration for 24 hr, then planted in moist vermiculite and allowed to germinate in the dark for about 65 hr at 23 to 25 C. The seedlings were next exposed to indirect light for about 24 hr. Single plants were then transferred to 4-liter glass jars of continuously areated nutrient solution consisting of 1 mM Ca (N03)

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“…Higher rates of transpiration may have led to greater tracer transport, but clearly further experiments are needed on this important point. There were too few different concentrations used to warrant comparison of transport and uptake at different levels of operation of mechanisms I and II as done by Hodges and Vaadia (1964). Using the same set of tissue %e was found to be 3·6fL-equiv.g-Ihr-1 in 0·5mM KCI and 4·9fL-equiv.g-Ihr-1 in IOmM KCl.…”

Section: Discussionmentioning

confidence: 99%

Uptake and Transport of Ions in Barley Seedlings I. Estimation of Chloride Fluxes in Cells of Excised Roots

Pitman¹

1971

Aust. Jnl. Of Bio. Sci.

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A comparison is made of transport of chloride through roots of barley seedlings, and the fluxes of chloride into the cells of the root estimated from efflux analysis. About 75% of tracer diffusing out of the cells in the root passes to the solution through the stele, but despite this complication it is considered that fluxes across plasmalemma and tonoplast could be estimated. It is shown that a model based on the sym. plasm theory can relate the specific activity of chloride transported to the shoot with the specific activity of a cytoplasmic phase calculated from the fluxes in the root cells.

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The Kinetics of Chloride Accumulation and Transport in Exuding Roots

Cited by 12 publications

References 16 publications

Radial Transport of Sodium and Chloride into Tomato Root Xylem

Radial Transport of Sodium and Chloride into Tomato Root Xylem

Accumulation and Radial Transport of Ions from Potassium Salts by Cucumber Roots

Uptake and Transport of Ions in Barley Seedlings I. Estimation of Chloride Fluxes in Cells of Excised Roots

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