On the Relationship between Extracellular pH and the Growth of Excised Pea Stem Segments

Parrish, David J.; Davies, Peter J.

doi:10.1104/pp.59.4.574

Cited by 35 publications

(19 citation statements)

References 29 publications

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“…In most of the published studies of hormone-induced H+ secretion using submerged segments, the segments have been stirred or shaken, but no additional precautions have been taken to assure adequate aeration, (1,10,12). Parrish and Davies (11), in a study of H+ efflux in pea stem segments, used aeration to agitate the segments and noted a strong dependence ofthe apparent rate of H+ secretion on the rate of aeration. We have compared auxin-induced H+ secretion in peeled corn coleoptile segments using stirring alone versus stirring supplemented with oxygenation (Fig.…”

Section: Resultsmentioning

confidence: 99%

An Improved Method for Detecting Auxin-induced Hydrogen Ion Efflux from Corn Coleoptile Segments

Evans

Vesper²

1980

Plant Physiol.

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Conditions necessary to detect maximal auxin-induced H+ secretion using a macroelectrode have been investigated using corn coleoptile segments. Auxin-induced H+ secretion is strongly dependent upon oxygenation or aeration when the tissue to volume ratio is high. Cuticle disruption or removal is also necessary to detect substantial auxin-induced H' secretion. The auxin-induced decrease in pH of the external medium is stronger when the hormone is applied to tissue in which the cuticle has been disrupted with an abrasive than when the hormone is applied to tissue from which the cuticle and epidermis have been removed by peeling. The lower detectable acidification ofthe external medium when using peeled segments appears to be due in part to the leakage of buffers into the medium and in part to the removal of the auxin-sensitive epidermal cells.The sensitivity of corn coleoptile segments to auxin, as measured by H+ secretion, increases about 2-fold during the first 2 hours after excision. Tlhis change in apparent sensitivity to auxin as reflected by H' secretion is paralleled by a time-dependent change in the growth response to auxin. Under optimal conditions for detecting H+ efflux (oxygenation, abrasion, hormone application 2 hours after excision), the latent period in auxininduced H+ efflux (about 7 or 8 minutes) is only half as great as the latent period in auxin-induced growth (about 18 to 20 minutes). These observations are consistent with the acid growth hypothesis of auxin action.According to the acid growth hypothesis of auxin action, auxin enhances growth by stimulating the secretion of H+ ions from the cytoplasm into the cell wall. The resultant acidification of the cell wall is thought to lead to wall loosening and accelerated growth (5,8,13,14).If auxin-induced H+ secretion acts as a mediator of auxininduced growth, one would expect hormone-induced H+ efflux to precede hormone-induced acceleration of growth. The most commonly used method of measuring H+ efflux is to place a large number (e.g. 40) of 1-cm long tissue segments in a small volume (e.g. 5 ml) of stirred weak buffer and monitor the change in pH of the medium in the presence and absence of hormone (12,14). Since the cuticle is said to offer substantial resistance to the entry and exit of H+ ions (3), it is common practice to remove the cuticle either by peeling the tissue segments with a pair of fine-tipped forceps or abrading them with emery powder. Using this method, auxin-induced H+ efflux appears to begin about 20 min or more after application of hormone (1,12,14) long apparent latent period in auxin-induced H+ secretion seems to be due, at least in part, to the large volume of the incubation solution compared with the volume of the cell wall fluid in which H+ would normally be accumulating. When the volume of the external medium is minimized, shorter latent periods are observed. Cleland (2), using a flat-tipped electrode resting on a row of peeled Avena coleoptile sections, reported an average latent period of 14 min in induction ...

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Section: Resultsmentioning

confidence: 99%

An Improved Method for Detecting Auxin-induced Hydrogen Ion Efflux from Corn Coleoptile Segments

Evans

Vesper²

1980

Plant Physiol.

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“…Following a short period of oxygen deprivation, oat coleoptiles [26,27] and pea stem segments [28,29] showed a temporary increase in growth rate when reimmersed in an aerated solution. During anaerobiosis the pH of the 'cell sap' (the 39000 x g supernatant following homogenization of oat coleoptiles in liquid Nz) dropped from 6.3 to 5.9, mainly due to an increase in lactic acid concentration [27].…”

Section: Discussionmentioning

confidence: 99%

Evidence that acid solutions induce plant cell elongation by acidifying the cytosol and stimulating the proton pump

1984

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Acetic acid (3 mM, pH 4.5) stimulated elongation growth of maize coleoptiles at a much higher rate than citric acid at the same pH and concentration. The effect of these solutions on cytosolic pH and membrane potential of maize rhizodermis cells was measured with microelectrodes. Citric acid caused a decrease in cytosolic pH and a slow membrane hyperpolarization. Acetic acid induced a larger and more rapid cytosolic acidification and membrane hyperpolarization. Hence, the degree of growth stimulation by the acids was positively correlated with the extent of their cytosolic acidification and stimulation of the proton pump. We suggest the acids induce growth by acidifying the cytosol and stimulating the proton pump rather than via direct acidification of the cell wall.

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“…A direct relationship between K+ and the sugar uptake mechanism of the phloem has recently been proposed (23). Potassium has been shown to stimulate H+ efflux from several plant tissues (17,23,26,28). If, as in algal (20) and bacterial (18) systems, sugar uptake is energetically linked to the inward flux of protons along their electrochemical gradient, an increase in proton concentration in the free space might be expected to enhance loading.…”

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confidence: 99%

Effect of Exogenously Supplied Foliar Potassium on Phloem Loading in Beta vulgaris L.

Doman

Geiger²

1979

Plant Physiol.

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The effect of foliar application of K' on processes associated with phloem loading was investigated in source leaves of sugar beet (Beta vulgaris L.). KCI was supplied exogenously at concentrations of up to 100 milimolar in the solution bathing the abraded upper epidermis of source leaves. K' added at concentrations below 30 millimolar generally promoted the rate of export of material derived from "CO2 but not from exogenously applied l14Cisucrose. Paralleling promotion of export, the level of material derived from photosynthesis, which was released into the bathing solution, also increased in response to addition of K+ to the free space. Net photosynthetic rate was not affected. K+ at 5 and 15 milimolar concentrations did not stimulate uptake of I'4Clsucrose into source leaf discs.The data suggest that the promotion of export rate by K+ results primarily from an effect on the site regulating efflux of sucrose into the apoplast prior to loading into the minor veins, rather than on the loading site itself. A change in the level of sucrose in the free space appears to precede a change in export rate.The presence of a relatively high concentration of K+, in the range of 20 to 100 mm, in phloem exudate (10,13,27) might be expected to promote sucrose uptake. However, the addition of K+ to sucrose solutions bathing cotyledons of R communis did not stimulate sucrose uptake (17,19).In an intact translocating plant there are several potential control points at which K+ could affect export. According to the model of phloem loading presented by Geiger and co-workers (4, 5, 31), sucrose destined for translocation moves from its site of synthesis in the mesophyll cells to the region of the phloem where it enters the apoplast prior to being loaded into the se-cc3 complex.The efflux site may be one of the points at which the rate of export is determined, with the efflux of assimilates being influenced by substances present in the apoplast.The present study examined the effect of application of exoge- or A-1 monogerm hybrid) were grown for 4 to 6 weeks by solution culture as previously described (7) or by sand culture in equal volumes of sand and Jiffy-Mix under the same light and temperature regime. The latter group was watered daily with the same mixture used for solution culture; K+ was present at 4 mm concentration. Photon flux density was 300 ILE m-2 s-1 at leaf level.Translocation Experiments. The closed gas flow system for steady-state labeling of source leaves was similar to that used by Geiger and Swanson (8). Light from a metal halide lamp produced a photon flux density of 300 ,uE m-2 s-' at leaf level. Plants were trimmed to a sink leaf/source leaf system at least 12 h prior to the experiment. The source leaf was abraded with a paste of 600-mesh aluminum oxide and distilled H20 to facilitate entrance of the bathing solution into the leaf free space (31).The leaf chamber (Fig. 1) After the source leaf was sealed in the chamber, a 10-to 12-ml volume of buffer was supplied to the abraded leaf surface. The expe...

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On the Relationship between Extracellular pH and the Growth of Excised Pea Stem Segments

Cited by 35 publications

References 29 publications

An Improved Method for Detecting Auxin-induced Hydrogen Ion Efflux from Corn Coleoptile Segments

An Improved Method for Detecting Auxin-induced Hydrogen Ion Efflux from Corn Coleoptile Segments

Evidence that acid solutions induce plant cell elongation by acidifying the cytosol and stimulating the proton pump

Effect of Exogenously Supplied Foliar Potassium on Phloem Loading in Beta vulgaris L.

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