Characterization of the transport and cellular compartmentation of paraquat in roots of intact maize seedlings

Hart, Jonathan J.; Tomaso, Joseph M. Di; Linscott, D. L.; Kochian, Leon V.

doi:10.1016/0048-3575(92)90034-w

Cited by 54 publications

(51 citation statements)

References 28 publications

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“…We have used this approach previously in several different studies to investigate the root compartmentation of a number of monovalent and divalent cations (Kochian and Lucas, 1982;Hart et al, 1992;DiTomaso et al, 1993;Lasat et al, 1997) and are very familiar with its limitations. This technique was developed to study ion compartmentation in single giant algal cells, in which the ion content of the individual compartments (vacuole, cytoplasm, and cell wall) can be measured directly (MacRobbie, 1971).…”

Section: Discussionmentioning

confidence: 99%

Altered Zn Compartmentation in the Root Symplasm and Stimulated Zn Absorption into the Leaf as Mechanisms Involved in Zn Hyperaccumulation in Thlaspi caerulescens

1998

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We investigated Zn compartmentation in the root, Zn transport into the xylem, and Zn absorption into leaf cells in Thlaspi caerulescens, a Zn-hyperaccumulator species, and compared them with those of a related nonaccumulator species, Thlaspi arvense. 65 Zncompartmental analysis conducted with roots of the two species indicated that a significant fraction of symplasmic Zn was stored in the root vacuole of T. arvense, and presumably became unavailable for loading into the xylem and subsequent translocation to the shoot. In T. caerulescens, however, a smaller fraction of the absorbed Zn was stored in the root vacuole and was readily transported back into the cytoplasm. We conclude that in T. caerulescens, Zn absorbed by roots is readily available for loading into the xylem. This is supported by analysis of xylem exudate collected from detopped Thlaspi species seedlings. When seedlings of the two species were grown on either low (1 M) or high (50 M) Zn, xylem sap of T. caerulescens contained approximately 5-fold more Zn than that of T. arvense. This increase was not correlated with a stimulated production of any particular organic or amino acid. The capacity of Thlaspi species cells to absorb 65 Zn was studied in leaf sections and leaf protoplasts. At low external Zn levels (10 and 100 M), there was no difference in leaf Zn uptake between the two Thlaspi species. However, at 1 mM Zn 2؉ , 2.2-fold more Zn accumulated in leaf sections of T. caerulescens. These findings indicate that altered tonoplast Zn transport in root cells and stimulated Zn uptake in leaf cells play a role in the dramatic Zn hyperaccumulation expressed in T. caerulescens.Phytoextraction is an emerging technology that involves the use of vascular plants to remediate soils contaminated with heavy metals and/or radionuclides (Nanda Kumar et al., 1995). This approach is based on the ability of higher plants to absorb contaminants from the soil and translocate them to their shoots. The identification of several metalhyperaccumulator plant species (Baker and Brooks, 1989;Baker et al., 1998) demonstrates that the genetic potential exists for successful phytoremediation of contaminated soils. One of the best-known metal hyperaccumulators is Thlaspi caerulescens J&C Presl, which has been reported to have a great potential for extraction of Zn and Cd from metalliferous soils (Reeves and

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Section: Discussionmentioning

confidence: 99%

Altered Zn Compartmentation in the Root Symplasm and Stimulated Zn Absorption into the Leaf as Mechanisms Involved in Zn Hyperaccumulation in Thlaspi caerulescens

1998

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“…Studies of the accumulation of severa1 different cations in roots have demonstrated that time-dependent cation uptake kinetics are biphasic, with an initial rapid component followed by a slower, linear phase of uptake (Veltrup, 1978;Korner et al, 1986;Zhang and Taylor, 1989;Hart et al, 1992). The rapid component has generally been interpreted to represent accumulation in the apoplasm, whereas the slower, linear phase is thought to be due to transport across the plasma membrane.…”

Section: Quantification Of 65znz+ Lnflux Into the Root Symplasmmentioning

confidence: 99%

“…To study the efficacy of our desorption procedure in removing cell-wall-bound Zn2+, time-course studies for the accumulation of 65Zn2+ were conducted with either roots of intact T. caerulescens seedlings or with morphologically intact root-cell-wall preparations. These cell-wall preparations were obtained by immersing roots of intact T. caerulescens seedlings in a MC (2:1, v / v ) solution for 3 d. We have previously shown in maize (Zea mays L.) roots that this treatment yields lipid-free root-cell-wall preparations that generally maintain the same shape and size of an intact root (Hart et al, 1992). Subsequent to the MC treatment, the root-cell-wall preparations were washed in a number of changes of deionized water for 12 h. Roots of either intact or MC-treated seedlings were incubated in radiolabeled uptake solution (10 p~ "Zn2+ , specific activity 1.4 pCi L-l, 0.5 mM CaCl,, and 2 mM Mes-Tris, pH 6.0) for time periods between 2 and 45 min, and then either briefly rinsed in deionized water (undesorbed) or desorbed in 1 L of desorption solution for 15 min.…”

Section: Time Course Of "Zn2+ Desorption From Rootsmentioning

confidence: 99%

“…caerulescens or T. aruense seedlings were immersed in 80 mL of pretreatment solution (2 mM Zn Transport in Hyperaccumulator Mes-Tris, pH 6.0, and 0.5 mM CaC1,) in individual Plexiglas wells of an uptake apparatus (Hart et al, 1992). Subsequently, Zn was added as ZnCI, to each uptake well to yield a final Zn concentration between 0.5 and 100 p~ 1 min before the addition of 0.08 pCi of 65ZnC1,.…”

Section: Concentration-dependent Kinetics Of "Znz+ Lnfluxmentioning

confidence: 99%

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Physiological Characterization of Root Zn2+ Absorption and Translocation to Shoots in Zn Hyperaccumulator and Nonaccumulator Species of Thlaspi

1996

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Radiotracer techniques were employed to characterize "Zn2+ influx into the root symplasm and translocation to the shoot i n Thlaspi caerulescens, a Zn hyperaccumulator, and Thlaspi arvense, a nonaccumulator. A protocol was developed that allowed us to quantify unidirectional 65Zn2+ i nflux across the root-cell plasma membrane (20 min of radioactive uptake followed by 15 min of desorption in a 100 p~ ZnCI, + 5 mM CaCI, solution).Concentration-dependent ZnZ+ influx in both Thlaspi species yielded nonsaturating kinetic curves that could be resolved into linear and saturable components. The linear kinetic component was shown to be cell-wall-bound Zn2+ remaining in the root after desorption, and the saturable component was due to Zn2+ influx across the root-cell plasma membrane. This saturable component followed Michaelis-Menten kinetics, with similar apparent Michaelis constant values for T. caerulescens and T. arvense (8 and 6 p~, respectively). However, the maximum initial velocity for ZnZ+ influx in T. caerulescens root cells was 4.5-fold higher than for T.arvense, indicating that enhanced absorption into the root is one of the mechanisms involved in Zn hyperaccumulation. After 96 h 1 O-fold more "Zn was translocated to the shoot of T. caerulescens compared with T. arvense. This indicates that transport sites other than entry into the root symplasm are also stimulated in T. caerulescens. We suggest that although increased root Zn2+ influx is a significant component, transport across the plasma membrane and tonoplast of leaf cells must also be critical sites for Zn hyperaccumulation in T. caerulescens.Recently, there has been an increased interest in the use of plants to decontaminate heavy-metal-polluted soils. In this process, called phytoremediation, higher plants are used to absorb contaminants from the soil into their roots and translocate them to shoots. Pollutants are subsequently removed by harvesting the above-ground tissues. This research area is lacking in basic information regarding the fundamental mechanisms employed by some plants to accumulate heavy metals in shoots.There is a small number of plant species capable not only of growing in soils containing high levels of heavy metals, '

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“…3), which predominates at high Zn 2ϩ activity in the uptake solution, can be interpreted as representing nonspecific Zn 2ϩ binding to cell wall components that remains after desorption. Evidence for divalent cation binding to root cell walls that resists desorption when exposed to high cation concentration has been observed previously Hart et al, 1992;Lasat et al, 1996). As a means of estimating Zn 2ϩ binding to wheat root cell walls, uptake was measured in intact roots exposed to low temperatures during the uptake period.…”

Section: Zn 2؉ Bindingmentioning

confidence: 99%

Characterization of Zinc Uptake, Binding, and Translocation in Intact Seedlings of Bread and Durum Wheat Cultivars

et al. 1998

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Durum wheat (Triticum turgidum L. var durum) cultivars exhibit lower Zn efficiency than comparable bread wheat (Triticum aestivum L.) cultivars. To understand the physiological mechanism(s) that confers Zn efficiency, this study used 65 Zn to investigate ionic Zn 2؉ root uptake, binding, and translocation to shoots in seedlings of bread and durum wheat cultivars. Time-dependent Zn 2؉ accumulation during 90 min was greater in roots of the bread wheat cultivar. Zn 2؉ cell wall binding was not different in the two cultivars. In each cultivar, concentration-dependent Zn 2؉ influx was characterized by a smooth, saturating curve, suggesting a carriermediated uptake system. At very low solution Zn 2؉ activities, Zn 2؉ uptake rates were higher in the bread wheat cultivar. As a result, the Michaelis constant for Zn 2؉ uptake was lower in the bread wheat cultivar (2.3 M) than in the durum wheat cultivar (3.9 M). Low temperature decreased the rate of Zn 2؉ influx, suggesting that metabolism plays a role in Zn 2؉ uptake. Ca inhibited Zn 2؉ uptake equally in both cultivars. Translocation of Zn to shoots was greater in the bread wheat cultivar, reflecting the higher root uptake rates. The study suggests that lower root Zn 2؉ uptake rates may contribute to reduced Zn efficiency in durum wheat varieties under Zn-limiting conditions.

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Characterization of the transport and cellular compartmentation of paraquat in roots of intact maize seedlings

Cited by 54 publications

References 28 publications

Altered Zn Compartmentation in the Root Symplasm and Stimulated Zn Absorption into the Leaf as Mechanisms Involved in Zn Hyperaccumulation in Thlaspi caerulescens

Altered Zn Compartmentation in the Root Symplasm and Stimulated Zn Absorption into the Leaf as Mechanisms Involved in Zn Hyperaccumulation in Thlaspi caerulescens

Physiological Characterization of Root Zn2+ Absorption and Translocation to Shoots in Zn Hyperaccumulator and Nonaccumulator Species of Thlaspi

Characterization of Zinc Uptake, Binding, and Translocation in Intact Seedlings of Bread and Durum Wheat Cultivars

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