Mechanisms of Passive Potassium Influx in Corn Mitochondria

Fluegel, M. Jane; Hanson, James A.

doi:10.1104/pp.68.2.267

Cited by 9 publications

(7 citation statements)

References 27 publications

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“…Plant mitochondria are permeable to C1-and K+ and thus swell passively when transferred to a hypertonic solution of KCI (7). Upon the addition of an oxidizable substrate (NADH), mitochondria contract in response to active efflux of ions from the matrix.…”

Section: Methodsmentioning

confidence: 99%

“…External KCl concentrations of 100 to 150 mm KCI do not result in a large K+ concentration gradient across the inner membrane because freshly isolated plant mitochondria contain 120 to 170 nmol K+/mg protein (7). As was the case with the hypertonic solution shown in Figure 1, the driving force lies with the Cl-gradient, and the rate of swelling is limited by the permeability to K+ of the inner membrane (7). The rate of Valinduced swelling of stressed shoot mitochondria was markedly greater than that of control shoot mitochondria (Fig.…”

Section: Methodsmentioning

confidence: 99%

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Effect of Osmotic Stress on Ion Transport Processes and Phospholipid Composition of Wheat (Triticum aestivum L.) Mitochondria

Klein

Burke²,

Wilson³

1986

Plant Physiol.

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The effect of osmotic stress on wheat (Triticum aestivum L.) mitochondrial activity and phospholipid composition was investipted. Preliminary growth measurements showed that osmotic stress (-0.25 or -0.5 megapascal external water potential) inhibited the rate of shoot dry matter accumulation while root dry matter accumulation was less sensitive. We have determined that differences in sensitivity to osmotic stress existed between tissues at the mitochondrial level. Mitochondria isolated from roots or shoots of stressed seedlings showed respiratory control and ADP/O ratios similar to control seedlings which indicates that stressed mitochondria were well coupled. However, under passive swelling conditions in a KCI reaction mixture, the rate and extent of valinomycininduced swelling of shoot mitochondria were increased by osmotic stress while root mitochondria were largely unaffected. Active ion transport studies showed efflux transport by stressed-shoot mitochondria to be partially inhibited since mitochondrial contraction required the addition of N-ethylmaleimide or nigericin. Efflux ion transport by root mitochondria was not inhibited by osmotic stress which indicates that stressinduced changes in ion transport were largely limited to shoot mitochondria. Characterization of mitochondrial fatty acid and phospholipid composition showed an increase in the percentage of phosphatidylcholine in stressed shoot mitochondria compared to the control. Mitochondrial fatty acid composition was not markedly altered by stress. No significant changes in either the phospholipid or fatty acid composition of stressed root mitochondria were observed. Hence, these results suggest that a tissue-specific response to osmotic stress exists at the mitochondrial level.Physiological responses of plants to water deficits generally vary with the severity and duration of the stress. The most sensitive processes are altered by a very mild stress and these changes intensify while additional processes become affected in accordance to their sensitivity to the stress (2).Sensitivity to water stress depends on the tissue in question. Under mild water stress, shoot growth is restricted while root growth continues (28,31 (1,15,22, 27), most have been restricted to water stress effects on shoot mitochondria while effects on root mitochondria have been neglected. Studies (1, 27) indicate that mitochondria isolated from air-dried shoots oxidize substrates (proline and to a lesser extent NADH, malate, and succinate) at reduced rates and exhibit generally poor coupling. These results and the lack of osmotic contraction by stmssed mitochondria (22) may indicate the loss ofmembrane integrity due to nonuniform shrinkage of mitochondrial membranes during desiccation (18). It should be emphasized that internal water deficits developed rather rapidly during air drying and became severe in a matter of hours.Because of the paucity of literature in this area, we examined the effect of mild osmotic stress on root and shoot mitochondrial ion and electron tra...

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Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Effect of Osmotic Stress on Ion Transport Processes and Phospholipid Composition of Wheat (Triticum aestivum L.) Mitochondria

Klein

Burke²,

Wilson³

1986

Plant Physiol.

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“…IC). Corn mitochondria have an H+/ K+ exchange mechanism which can function in passive uptake of KCl and K-acetate (8). If a H +/citrate symport also exists, passive uptake of potassium citrate driven by a high external citrate concentration should occur, and the uptake should be stimulated by the uncoupler FCCP, or by the H+/K+-exchanging ionophore nigericin (Fig.…”

mentioning

confidence: 99%

“…electrogenic), similar to Cl-influx (8), then valinomycin, the K+ ionophore, should stimulate citrate uptake and swelling. There is another distinction here: in the case of chloride transport by uniport an increase in pH increases passive swelling (8), and one might expect a similar effect here for a citrate uniport; with co-transport of protons, decreasing the pH would increase the concentration of one of the two transported ions and therefore be likely to increase swelling.…”

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confidence: 99%

Citrate Transport in Corn Mitochondria

Birnberg

Jayroe²,

Hanson³

1982

Plant Physiol.

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is not yet understood.It is widely accepted that the transport of Krebs cycle substrate anions by plant mitochondria is by the DC2 and TC transporters disclosed in studies with animal mitochondria (reviewed in Refs. 11 and 30; for animal mitochondria, see Ref. 18). The principal evidence is found in the exchange studies of De Santis et a!. (7), and in passive swelling studies with isosmotic solutions of NH4' salts (25,29). The general conclusion is that the primary transport lies with the exchange of Pi for OH-(or symport of Pi with H+), with DC (e.g. malate, succinate) exchanging for Pi, and TC (e.g. citrate, isocitrate) exchanging for DC (Fig. IA) driven by endogenous respiration or ATP (21).In the work reported here we have used both swelling and ['4C] citrate uptake to study citrate transport in corn mitochondria. There is definitely a mechanism that is not dependent on phosphate or malate transport, and which has characteristics of a H +/ citrate symport (Fig. 1, B and C; see "Discussion").MATERIALS AND METHODS Mitochondria. Corn (Zea mays L. B73 x Mol9) shoot mitochondria were isolated as described ( 17)

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“…This paper reports that several other anions are taken up by the same or a similar mechanism, but less effectively, and only isocitrate is a strong competitive inhibitor of citrate uptake. We also report (9,13). When the H -symported anion penetrates slowly ('high resistance'), as in the case of sulfate, the addition of valinomycin opens the H+/K+ antiport as the pathway of least resistance to proton influx, and the mitochondria are, in effect, partially uncoupled in cyclic potassium transport (10).…”

mentioning

confidence: 70%