Interactions between Cytoplasm and Vacuole

Matile, Philippe; Wiemken, Andres

doi:10.1007/978-3-642-66417-5_8

Cited by 20 publications

(9 citation statements)

References 118 publications

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“…During the short incubation periods (0.5 to 1 h) utilized in almost all of our experiments, most of the radioactive sucrose accumulated probably stayed as such (Fig. 8) (14). This may well be true also in soybean embryos.…”

Section: Plant Growth Nodulated Plants Of Soybean (Glycine Max [L]supporting

confidence: 52%

Characterization of the Active Sucrose Transport System of Immature Soybean Embryos

Thorne

1982

Plant Physiol.

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Immature soybean embryos were isolated from soybean lG4vcine max (L.) Merr Active transport is sensitive to uncoupling agents and the suHhydrylmodifying reagent p-chloromecuribenzene sulfonate, is dependent on more than one energy source, and exhibits well-defined requirements for incubation temperature, pH, and oxygen availability. Under optimal incubation conditions of 35°C, saturating illumination (pH 6), and 21% oxygen, the apparent Km for sucrose is approximately 8 millimolar and V,,. is approximately 0.6 micromoles per hour per 100 milligrams fresh weight. Embryos readily accumulate sucrose from dilute exogenous solutions and, when preloaded with large amounts of sucrose, maintain the internal sucrose pool against steep outward gradients. These and other observations indicate that, although perhaps fully saturated in vivo, active sucrose transport is a significant component of photosynthate uptake in developing soybean embryos, enhancing uptake at physiological sucrose concentrations 2-to 5-fold over diffusion alone.It is tacitly agreed that photosynthate production rather than phloem transport capacity controls photosynthate availability and thus crop productivity. There is growing evidence, however, that processes that may limit the rate of photosynthate uptake and utilization in developing sink tissues may also play an important regulatory role (7,23,24, 27, 28). Among soybeans, for example, genetic differences in seed growth rate and final size appear to be determined more by the number of cells in the embryo than by the photosynthate supply from the leaves (4). This suggests that the rate of sucrose uptake and utilization by embryos on a per cell basis may be similar across soybean cultivars. But not enough is known about these processes to assess their role as determinants of sink strength, carbon partitioning, or economic yield. was provided by a mixture of incandescent and Sylvania cool white fluorescent lamps. Principal growth conditions (24/18°C, 12-h photoperiod) favored rapid seed development. Undamaged embryos of 300 to 400 mg FW' were excised from developing seeds and used for the following experiments. Sucrose Uptake Experiments. Unless otherwise specified, these experiments were performed with complete embryos (embryonic axis attached to both cotyledons), 300 to 400 mg FW, excised 20 to 30 min prior to each experiment. As the seed coats were removed, the embryos were transferred to 5 mm Mes buffer (pH 6.0) at room temperature until sufficient numbers were obtained.All embryos were then subjected to a 20-min pretreatment in aerated Mes buffer before incubation in ["4CJsucrose. Inhibitors, when used, were introduced for this 20-min period. PCMBS was not present during the subsequent '4C uptake period but, instead, any excess was washed from the embryo free space with buffer (three 3-min washes) before '4C incubation. These procedures were used to focus the PCMBS action on the sucrose-translocating protein rather than energy-coupling component (i.e. ATPase) of the active uptake syst...

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Section: Plant Growth Nodulated Plants Of Soybean (Glycine Max [L]supporting

confidence: 52%

Characterization of the Active Sucrose Transport System of Immature Soybean Embryos

Thorne

1982

Plant Physiol.

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“…For Mn2+ and Ca2+, it has been found that the vacuole is the major cellular compartment (Okorokov et al, 1977;Eilam et al, 1985) which is apparently advantageous to the cell in that the metal is localized and potentially damaging effects are limited (Matile & Wiemken, 1976). The vacuolar membrane possesses an ATPdependent transport system for basic amino acids Ohsumi & Anraku, 1981) and Ca2+ (Ohsumi & Anraku, 1983;Eilam et al, 1985) and a range of heavy metals can affect vacuolar ATPase activity in vitro and alter the H+ gradient across the vacuolar membrane (Okorokov, 1985).…”

Section: Introductionmentioning

confidence: 99%

The Uptake and Cellular Distribution of Zinc in Saccharomyces cerevisiae

White

Gadd

1987

Microbiology

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Zn2+ uptake by Saccharomyces cerevisiae was biphasic. The first phase was independent of metabolic energy, consisting of adsorption to the cell surface, and followed a Freundlich isotherm. The second phase was dependent on metabolic energy, ATPase activity and the transmembrane proton gradient, and consisted of uptake into the cell. Energy-dependent uptake showed Michaelis-Menten kinetics with a K , of 3-7 pM-Zn2+ and a V,,, of 1.6 nmol min-l per lo7 cells at Zn2+ concentrations below 8 0 p~ but deviated at higher concentrations. K+ and Mg2+ inhibited energy-dependent Zn2+ uptake while Na+ and Ca2+ did not. The effect of heavy metals was complex and included both inhibition and stimulation of Zn2+ uptake. K+ efflux accompanied Zn2+ uptake at all Zn2+ concentrations but there was no simple stoichiometric relationship between the two. Toxic effects of Zn2+ such as inhibition of H+ efflux and K+ uptake and reduction of viability were observed at all Zn2+ concentrations and toxicity appeared to be a major factor in K+ efflux. Toxicity also affected the kinetics of Zn2+ uptake, being a major cause of deviation from Michaelis-Menten kinetics. Zn2+ was compartmented within the cell: 56% of the total intracellular pool was in the soluble vacuolar fraction, 39% was bound to insoluble components and only 5 % was found in the cytosol. Isolated yeast vacuoles possessed an ATP-dependent Zn2+ uptake system whose properties were consistent with a Zn2+/H+ antiport.

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“…tonoplast has so far not been adduced. Technical difficulties seem to have prevented uptake studies from being carried out on higher plant vacuoles in the past (12). We recently developed techniques for observing membrane transport in isolated protoplasts (4) and have now extended our studies to vacuoles released from these protoplasts.…”

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confidence: 99%

Direct Evidence for a Sugar Transport Mechanism in Isolated Vacuoles

Guy

Reinhold²,

Michaeli³

1979

Plant Physiol.

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Sugar transport has been directly observed in isolated higher plant vacuoles for the first time. The latter were released from protoplasts isolated from the mesophyli of Pisum sativum L.Uptake of L-glucose by the vacuoles was very slight in comparison with that of the D-glucose analog 3-0-methyl glucose (MeG), indicating, first, that a highly selective sugar uptake mechanism is seated in the tonoplast; and, second, that the mechanism was functioning in the isolated vacuoles.MeG uptake was markedly sensitive to the pH of the medium, failing as the external pH rose. Addition of MgATP to buffered medium strongly promoted MeG uptake by vacuoles, but not by the protoplasts from which they were released. Treatment with the proton ionophore SF&W7 drastically reduced uptake by the vacuoles, but had a lesser effect on uptake by the protoplasts. The inhibitory effect of SFWW7 on uptake by the vacuoles was countered to a substantial degree by the addition of MgATP.The influence of pH, the stiiuulatory effect of ATP, and the ATPreversible inhibition by SFWM7 all strengthen the conclusion that the observed sugar uptake reflected membrane function and was not due to a diffusional inward leak through damaged membranes.The results are discussed in the light ofcurrently held concepts regarding the driving force for sugar transport.The question as to whether various membrane transport mechanisms are sited in the plasmalemma or the tonoplast has interested plant physiologists for a considerable period (e.g. 2). Evidence with regard to this siting in higher plant cells has until very recently been entirely indirect, based in large part on measurement of over-all fluxes across both plasmalemma and tonoplast. Lately, however, a start has been made in locating components of transport mechanisms at the membrane level. Membrane fractions rich in ATPase activity have been isolated (5). These membrane preparations have of necessity been of mixed origin, but it has been deduced that certain of the fractions consisted to a large extent of plasmalemma (5 tonoplast has so far not been adduced. Technical difficulties seem to have prevented uptake studies from being carried out on higher plant vacuoles in the past (12). We recently developed techniques for observing membrane transport in isolated protoplasts (4) and have now extended our studies to vacuoles released from these protoplasts. In the present communication we report studies on sugar uptake by isolated vacuoles, and bring direct evidence for the location of a selective sugar transport mechanism in the tonoplast. MATERIALS AND METHODSPisum sativum L. var. Dan were grown in a growth chamber at 24 C and a photoperiod of 12 h. When the second leaf was almost fully expanded the terminal leaflet pair was excised for experiment. Details of the procedure for isolation of mesophyll protoplasts and of the composition of the suspension medium have already been reported (4).Vacuoles were released from the protoplasts by the shearing force of ultracentrifugation through a step-density gra...

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Interactions between Cytoplasm and Vacuole

Cited by 20 publications

References 118 publications

Characterization of the Active Sucrose Transport System of Immature Soybean Embryos

Characterization of the Active Sucrose Transport System of Immature Soybean Embryos

The Uptake and Cellular Distribution of Zinc in Saccharomyces cerevisiae

Direct Evidence for a Sugar Transport Mechanism in Isolated Vacuoles

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