Probable Role of Allylisothiocyanate-Sensitive H+, K+-ATPase in Spicule Calcification in Embryos of the Sea Urchin, Hemicentrotus pulcherrimus

In embryos of the sea urchin, Hemicentrotus pulcherrimus , as well as in cultured cells derived from isolated micromeres, spicule formation was inhibited by allylisothiocyanate, an inhibitor of H⁺, K⁺-ATPase, at above 0.5 μM and was almost completely blocked at above 10 μM. Amiloride, an inhibitor of Na⁺, H⁺ antiporter, at above 100 μM exerted only slight inhibitory effect, if any, on spicule formation. Intravesicular acidification, determined using [ dimethylamine -¹⁴C]-aminopyrine as a pH probe, was observed in the presence of ATP and 200 mM KCl in microsome fraction obtained from embryos at the post gastrula stage, at which embryos underwent spicule calcification. Intravesicular acidification and K⁺-dependent ATPase activity were almost completely inhibited by allylisothiocyanate at 10 μM. Allylisothiocyanate-sensitive ATPase activity was found mainly in the mesenchyme cells with spicules isolated from prisms. H⁺, K⁺-ATPase, an H⁺ pump, probably mediates H⁺ release to accelerate CaCO₃ deposition from Ca²⁺, CO₂ and H₂O in the primary mesenchyme cells. Intravesicular acidification was stimulated by valinomycin at the late gastrula and the prism stages but not at the pluteus stage. K⁺ permeability probably increases after the prism stage to activate H⁺ release.     

Influence of phytohormones and other effectors on proton extrusion by isolated protoplasts from rape leaves

The roles of phytohormones and fusicoccin in H⁺ extrusion by isolated protoplasts from rape leaves ( Brassica napus L. cv. Belinda) were investigated and compared to results obtained with leaf segments of the same plants. Net H⁺ release by protoplasts, which was at least partly due to ATPase activity, was enhanced by 10 μ M indole-3-acetic acid and reduced by 20 μ M abscisic acid, whereas fusicoccin (10 μ M ), brassinosteroid (3 μ M ), kinetin (20 μ M ) and gibberellic acid (10 μ M ) had no effect. Hormone effects and H⁺ release were not detectable with leaf segments from the same plants. However, using field-grown plants, indole-3-acetic acid and especially fusicoccin stimulated the acidification of the external medium by leaf segments. Hormonecontrolled H⁺ release by leaf cells is interpreted as the first step in acid-triggered and turgor-regulated cell growth.     

Effects of UV-C radiation on extension growth, H+-extrusion and transmembrane electric potential in maize coleoptile segments

The effect of 253.7 nm ultraviolet radiation on elongation growth, medium acidification and changes in electric potential difference between vacuole and external medium in cells of maize ( Zea mays L.) coleoptile segments was investigated. It was found that irradiation with 390, 1170, 3900 and 5 850 J m⁻² UV-C (ultraviolet radiation 253.7 nm) inhibited elongation growth, whereas at 195 J m⁻² stimulation of growth was observed. The administration of IAA (10⁻⁵ M ) to the incubation medium of coleoptile segments partially abolished the inhibitory effect of UV-C. The pH of the incubation medium, measured simultaneously with growth, showed that the exposure of the segments to UV-C caused inhibition of H⁺-extrusion (or stimulation of H⁺ uptake). The presence of IAA (10⁻⁵ M ) in the incubation medium promoted (except after 5850 J m⁻² irradiation) H⁺-extrusion to a level comparable with that produced by IAA in non-irradiated segments. In UV-C irradiated segments the potential difference underwent significant alterations. Irradiation of coleoptile segments with 390 J m⁻² caused a transient depolarization, which was fully reversible within 30 min, while at higher doses depolarization was irreversible. The hyperpolarization of the membrane potential (MP) in cells of maize coleoptile induced by IAA was completely nullified by subsequent irradiation with UV-C. It is suggested that UV-C inhibited IAA-induced growth by a mechanism independent of cell wall acidification.     

Monitoring of aluminium-induced inhibition of root elongation in four maize cultivars differing in tolerance to aluminium and proton toxicity

Four maize cultivars, which differ in tolerance to acid soils under field conditions ( Zea mays L., acid soil-tolerant C 525 M, BR 201 F and Adour 250, and acid soil-sensitive HS 7777) were used to study the influence of pH (4.3 and 6.0) and Al (0, 20 and 50 μ M ) on the elongation of seminal roots in nutrient solution. Root elongation was inhibited by high H⁺ concentrations (pH 4.3) in cultivars C 525 M, Adour 250 and HS 7777 but not in BR 201 F. After 20 h exposure to Al, root elongation rates were more inhibited in cultivars BR 201 F and HS 7777 than in C 525 M and Adour 250. The use of a computerized linear displacement transducer system with high resolution (1 μm) allowed the monitoring of short-term responses of root elongation to Al. In the three cultivars affected by H⁺ toxicity, but not in the acid-tolerant BR 201 F, Al supply caused an immediate, but transient increase of relative root elongation rates. This result supports the hypothesis that Al-induced growth stimulation is caused by amelioration of proton toxicity. The time required for 20 μ M Al to induce a 5% decrease of root elongation rates was shorter in the Al-sensitive BR 201 F (33 min) and HS 7777 (86 min) than in the Al-tolerant C 525 M (112 min) and Adour 250 (146 min) cultivars. However, the response-time to Al may be overestimated in the proton-sensitive cultivars, due to the transient stimulation of root elongation rates induced by Al. According to our results, experiments intended to investigate primary mechanisms of Al toxicity should be started after less than 30 min exposure to toxic Al concentrations, using pH conditions which avoid Al-induced growth stimulation due to amelioration of proton toxicity.     

The tonoplast H+-pyrophosphatase of radish seedlings: biochemical characteristics

The activity of the H⁺-pyrophosphatase (H⁺-PPase) was characterized in microsomes from 24-h-old radish ( Raphanus sativus L., ev. Tondo Rosso Quarantino) seedlings, which are virtually devoid of the tonoplast H⁺-ATPase. The H⁺-PPase was localized to membranes which roughly comigrated with the plasma membrane in a sucrose density gradient, but clearly separated from plasma membrane when microsomes were partitioned in an aqueous dextran-polyethylene glycol two-phase system. The H⁺-PPase activity was strictly dependent on Mg²⁺ and on the presence of a monovalent cation (K⁺=Rb⁺=NH₃⁺Cs⁺≫Na⁺Li⁺) and was insensitive to anions such as Cl−, Br−, NO₃− and SO₄^2-. It was inhibited by F−, imidodiphosphate and Ca²⁺. It had a pH optimum between pH 7.5 and 8.5 and was saturated by low concentrations of pyrophosphate (half saturation at 30 μ M pyrophosphate). All of these characteristics are identical to those reported for the tonoplast H⁺-PPase from various plant materials. The functional molecular weight of the H⁺-PPase, measured with the radiation-inactivation technique was 96 kDa.     

Benzyladenine-induced stimulation of 5-aminolevulinic acid accumulation under various light intensities in levulinic acid-treated cotyledons of etiolated cucumber

Benzyladenine (BA) stimulated 5-aminolevulinic acid (ALA) accumulation in the presence of levulinic acid during illumination with 43 μmol m⁻² s⁻¹ light in excised etiolated cotyledons of cucumber ( Cucumis sativus L. cv. Aonagajibai). A short dark-pretreatment (6 h) with BA eliminated the lag phase of ALA accumulation. The rate of ALA accumulation during the steady-state phase in cotyledons pretreated with BA for a long period (14 h) was considerably accelerated compared to that in cotyledons pretreated with BA for 6 h. The rate of ALA accumulation during the lag phase was saturated at a very low light fluence (<1.4 μmol m⁻² s⁻¹) in both BA-pretreated and water-control cotyledons. The steady-state rate of ALA accumulation increased with increasing light fluence up to 43 μmol m⁻² s⁻¹ (parallel to that of Chl formation) in water-control cotyledons. In contrast, in cotyledons pretreated with BA for either 6 or 14 h, the steady-state rate reached a plateau at a very low light fluence. Based on the above results together with our finding that there are two components of Chl formation (M. Dei, 1984. Physiol. Plant. 62: 521–526) possible intermediate steps of Chl biosynthesis pathway affected by BA and light intensity are discussed.     

Influence of copper on proton efflux from Saccharomyces cerevisiae and the protective effect of calcium and magnesium

Abstract The inhibitory effect of Cu on glucose-dependent H⁺ efflux from Saccharomyces cerevisiae was manifest at low (micromolar) concentrations, with the time period between the addition of glucose and commencement of H⁺ efflux, H⁺ efflux rate and duration all being affected with increasing Cu concentration (5–100 μM). Ca, at a concentration of 0.5 mM, completely removed the inhibitory effect of Cu at concentrations up to 50 μM and considerably reduced it at higher concentrations (up to 150 μM). Mg exhibited a similar but weaker protective effect against the influence of Cu. The protective effect of Ca against 50 μM Cu was evident at low Ca concentrations (2.5–5 μM), whereas Mg was effective at ≥50 μ M. In order to prevent the inhibitory effect of Cu, it was necessary to add Ca or Mg to the cell suspension before Cu addition. It is concluded that the protective effect of Ca and Mg is mediated by competitive and stabilizing interactions at the cell surface as well as physiological functions of Ca and Mg.     

Effects of a brassinosteroid on growth and electrogenic proton extrusion in Azuki bean epicotyls

Brassinolide, a plant hormone newly isolated from pollen, promotes growth of the stem of a number of plant species. Similar effects are induced by a brassinosteroid (BR), the synthetic 24-epibrassinolide. In this paper the effects of BR on acid secretion and transmembrane electrical potential difference in Azuki bean ( Vigna angularis , Ohwi and Ohashi cv. Takara) epicotyls were determined in short term experiments and compared with the effects on growth. At concentrations between 10^-7 to 10^-5 M , BR stimulates, similarly to indole-3-acetic acid (IAA), growth and H⁺ extrusion and hyperpolarizes the transmembrane electric potential (PD). These effects of BR, as well as those of IAA, are suppressed by inhibitors of RNA and protein synthesis. All these effects of BR and IAA appear roughly additive, even when both hormones are present at their optimal concentrations. The data are interpreted as showing that the action of BR on growth is at least in part mediated by its capability to activate electrogenic proton extrusion. The additivity of the effects of BR and IAA suggests that the primary mechanism of action of the two hormones is different.     

Changes in ethanol, lactate and malate content in Acer pseudoplatanus cells: effects of fusicoccin and O2 availability

Changes in the contents of ethanol, lactate and malate were determined at different activities of the plasma membrane H⁺ pump [in the presence and absence of fusicoccin (FC)] and at different O₂ availability in cultured cells of Acer pseudoplatanus L. FC induced acidification of the medium under all tested conditions of O₂ availability. At low O₂ concentrations both ethanolic and lactic fermentations occurred, and FC markedly stimulated lactate production but had no effect on ethanol production. There was also a small, stimulating effect of FC on malate production. At high O₂ concentrations no ethanol production was observed and lactate production was reduced. Under these conditions the stimulating effect of FC on lactate production decreased, while that on malate production increased. FC-induced synthesis of lactate and malate is interpreted as depending on the activation of lactate dehydrogenase (EC 1.1.1.27) and phosphoenolpyruvate carboxylase (EC 4.1.1.31) (alkaline pH optima), respectively, due to the alkalinization of the cytoplasmic pH resulting from the stimulation of the H⁺ pump by FC. These results suggest that the balance between the two pH stat systems depends on the availability of O₂.     

Benzyladenine-induced stimulation of two components of chlorophyII formation in etiolated cucumber cotyledons

Excised etiolated cotyledons of cucumber ( Cucumis sativus L. cv. Aonagajibai) were continuously irradiated under various intensities of white light. The rate of chlorophyII (Chi) formation during the lag phase reaches a plateau at fluence rates above 1.4 urmol m⁻² s⁻¹. This is true in both water-control and benzyladenine (BA)-pretreated cotyledons. In cotyledons pretreated for 14 h with BA in darkness (in which case, Chl formation is stimulated by BA during both the lag and the steady-state phases), the increase in the steady-state rate of Chl formation with increasing light in tensity is stimulated compared to that of the water control over the range of fluence rates, 0. 25-43 urmol m⁻² s⁻¹. In cotyledons pretreated for 6 h with BA in darkness (only Chl formation during the lag phase is stimulated), only an increase in fluence rate from 0.25 to 1.4 umol m⁻² s⁻¹ causes a higher increase in the Chl formation in the BA-treated cotyledons than in the water control. The time course of Chl formation shows that the BA-induced late-appearing effect (stimulation of the steady-state rate) is almost absent at low intensity illumination, but the BA-induced fast-appearing effect (elimination of the lag phase) is effective at all intensities. From this evidence, the Chl-forming process apparently consists of two components, whose periods of operation or light-intensity requirements are different. BA stimulates the rates of the respective components in both the fast and the late-appearing effects.     

Inhibition of brassinosteroid-induced epinasty in tomato plants by aminooxyacetic acid and Co2+

The inhibitory effects of aminooxyacetic acid (AOA) and cobalt chloride (CoCl₂) on brassinosteroid (BR)-induced epinasty in tomato plants ( Lycopersicon esculentum Mill. cv. Heinz 1350) are evaluated. CoCl₂ dramatically decreases petiole bending and ethylene production as the concentration increases from 50 to 200 μ M. The content of 1-aminocyclopropane-1-carboxylic acid (ACC) in the petiole, instead of accumulating, is reduced and does not change over the concentration range tested. Inhibition of BR-induced epinasty by AOA results from inhibition of ACC synthesis. There are dramatic reductions in petiole bending, ethylene and ACC production as the concentration of AOA is increased from 50 to 200 μ M. Maximum inhibition occurs when the plants are pretreated with the inhibitors. The degree of inhibition increases as the length of pretreatment increases from 1 to 4 h. The response of BR-treated plants to AOA and CoCl₂ is similar to the effect of auxin, indicating the integral relationship between BR and auxin.     

A Phosphopeptide Corresponding to the Cytosolic Stretch Connecting Transmembrane Segments 8 and 9 of the Plasma Membrane H+-ATPase Binds 14-3-3 Proteins and Inhibits Fusicoccin-Induced Activation of the H+-ATPase

Abstract: A putative consensus domain for binding of 14-3-3 proteins to the plasma membrane (PM) H⁺-ATPase was identified in the highly-conserved sequence RSR(p)SWSF [where (p)S is Ser776 of the maize isoform MHA2], localized in the cytosolic stretch connecting transmembrane segments 8 and 9. A 15 amino acid biotinylated phosphopeptide comprising this motif: i) bound a recombinant 14-3-3 protein, ii) inhibited fusicoccin-induced stimulation of the PM H⁺-ATPase activity both in PM isolated from germinating radish ( Raphanus sativus L.) seedlings and in ER isolated from Saccharomyces cerevisiae expressing AHA1 (an isoform of Arabidopsis thaliana PM H⁺-ATPase), and iii) inhibited fusicoccin binding to PM isolated from germinating radish seedlings. The corresponding non-phosphorylated peptide was inactive in all the performed assays. Together, these results suggest that the cytosolic strand connecting transmembrane segments 8 and 9 of the PM H⁺-ATPase is a 14-3-3 binding site which might cooperate with the C-terminal domain of the'enzyme in generating a stable association between the H⁺-ATPase and 14-3-3 protein.     

Stimulation of chlorophyll synthesis by benzyladenine and potassium in excised and intact cucumber cotyledons

Both benzyladenine (BA) and potassium (K) stimulated chlorophyll synthesis in cucumber ( Cucumus sativus L. cv. National Pickling) cotyledons. However, differences existed between the effects of BA and K. Stimulation of chlorophyll synthesis by BA (1 mg l⁻¹, 4.4 μ M ) was observed in excised cotyledons after 4 and 8 h of illumination but not after 24 h, whereas the stimulation caused by K (40 m M ) continued. In contrast to BA, K was unable to eliminate the lag phase of chlorophyll production, and it also required light for its stimulation of cotyledon expansion. Both BA and K were required to maximize cotyledon expansion and chlorophyll production. In intact plants, K was not limiting for chlorophyll synthesis since foliar or soil pretreatments with K did not markedly stimulate greening. Foliar pretreatment with BA stimulated chlorophyll levels in intact plants, whereas soil pretreatment with BA inhibited chlorophyll production, probably because BA was not readily transported from the roots to the shoot and created a "sink" effect. Inhibitor studies showed that stimulation by K of greening did not depend on RNA or chloroplastic protein synthesis to the extent that has been reported for BA. Thus it appears that BA and K stimulate chlorophyll synthesis via different mechanisms, although both cytokinins and K are essential for maximum rates of greening.     

Synergistic activation of plasma membrane H+– ATPase in Arabidopsis thaliana cells by turgor decrease and by fusicoccin

The regulation of the H⁺-ATPase of plasma membrane is a crucial point in the integration of transport processes at this membrane. In this work the regulation of H⁺-ATPase activity induced by changes in turgor pressure was investigated and compared with the stimulating effect of fusicoccin (FC). The exposure of cultured cells of Arabidopsis thaliana L. (ecotype Landsberg 310–14-2) to media containing mannitol (0. 15 or 0. 3 M ) or polyethylene glycol 6000 (PEG) (15. 6% or 22% w/v) resulted in a decrease in the turgor pressure of the cells and in a strong stimulation of H⁺ extrusion in the incubation medium. The osmotica-induced H⁺ extrusion was (1) inhibited by the inhibitor of plasma membrane H⁺-ATPase, erythrosin B (EB), (2) dependent on the external K⁺ concentration, (3) associated with a net K⁺ influx, and (4) lead to an increase of cellular malate content. These results show that the reduction of external osmotic potential stimulates the activity of plasma membrane H⁺-ATPase
The effect of mannitol was only partially inhibited by treatments with cycloheximide (CH) and cordycepin, which block protein and mRNA synthesis, respectively. All the effects of osmotica were qualitatively and quantitatively similar to those induced by 5 μ M FC. However, when FC and mannitol (or PEG) were fed together, their effects on H⁺ extrusion appeared synergistic, irrespective of whether FC was present at suboptimal or optimal concentrations. This behaviour suggests that the modes of action of FC and of the osmotica on H⁺-ATPase activity differ at least in some step(s)     

The halophilic alkalithermophile Natranaerobius thermophilus adapts to multiple environmental extremes using a large repertoire of Na+(K+)/H+ antiporters

Natranaerobius thermophilus is an unusual extremophile because it is halophilic, alkaliphilic and thermophilic, growing optimally at 3.5 M Na⁺, pH^55°C 9.5 and 53°C. Mechanisms enabling this tripartite lifestyle are essential for understanding how microorganisms grow under inhospitable conditions, but remain unknown, particularly in extremophiles growing under multiple extremes. We report on the response of N. thermophilus to external pH at high salt and elevated temperature and identify mechanisms responsible for this adaptation. N. thermophilus exhibited cytoplasm acidification, maintaining an unanticipated transmembrane pH gradient of 1 unit over the entire extracellular pH range for growth. N. thermophilus uses two distinct mechanisms for cytoplasm acidification. At extracellular pH values at and below the optimum, N. thermophilus utilizes at least eight electrogenic Na⁺(K⁺)/H⁺ antiporters for cytoplasm acidification. Characterization of these antiporters in antiporter-deficient Escherichia coli KNabc showed overlapping pH profiles (pH 7.8–10.0) and Na⁺ concentrations for activity ( K _0.5 values 1.0–4.4 mM), properties that correlate with intracellular conditions of N. thermophilus . As the extracellular pH increases beyond the optimum, electrogenic antiport activity ceases, and cytoplasm acidification is achieved by energy-independent physiochemical effects (cytoplasmic buffering) potentially mediated by an acidic proteome. The combination of these strategies allows N. thermophilus to grow over a range of extracellular pH and Na⁺ concentrations and protect biomolecules under multiple extreme conditions.     

Plasma membrane H+-ATPase-dependent citrate exudation from cluster roots of phosphate-deficient white lupin

White lupin ( Lupinus albus L.) is able to grow on soils with sparingly available phosphate (P) by producing specialized structures called cluster roots. To mobilize sparingly soluble P forms in soils, cluster roots release substantial amounts of carboxylates and concomitantly acidify the rhizosphere. The relationship between acidification and carboxylate exudation is still largely unknown. In the present work, we studied the linkage between organic acids (malate and citrate) and proton exudations in cluster roots of P-deficient white lupin. After the illumination started, citrate exudation increased transiently and reached a maximum after 5 h. This effect was accompanied by a strong acidification of the external medium and alkalinization of the cytosol, as evidenced by in vivo nuclear magnetic resonance (NMR) analysis. Fusicoccin, an activator of the plasma membrane (PM) H⁺-ATPase, stimulated citrate exudation, whereas vanadate, an inhibitor of the H⁺-ATPase, reduced citrate exudation. The burst of citrate exudation was associated with an increase in expression of the LHA1 PM H⁺-ATPase gene, an increased amount of H⁺-ATPase protein, a shift in pH optimum of the enzyme and post-translational modification of an H⁺-ATPase protein involving binding of activating 14-3-3 protein. Taken together, our results indicate a close link in cluster roots of P-deficient white lupin between the burst of citrate exudation and PM H⁺-ATPase-catalysed proton efflux.     

Fusicoccin, an inhibitor of brassinosteroid-induced ethylene production

Fusicoccin was evaluated for its effects on brassinosteroid (BR), indole-3-acetic acid (IAA) and BR + IAA-induced ethylene, 1-aminocyclopropane-1-carboxylic acid (ACC) and ACC-synthase production by etiolated mung bean ( Vigna radiata L. Rwilez cv. Berken) hypocotyl segments. Fusicoccin inhibition of ethylene and ACC production induced by 2 μ M BR started at concentrations as low as 0.05 μ M . Maximum inhibition occurred at a 1 μ M concentration with no further inhibition at higher concentrations tested. Fusicoccin (1 μ M ) was effective in the inhibition of BR-induced ethylene, ACC and ACC-synthase production at low and high concentrations of BR.
Fusicoccin at concentrations as high as 2 μ M had no effect on ethylene and ACC production promoted by low concentrations of IAA (1 to 10 μ M ). When higher concentrations (100–1000 μ M ) of IAA were used, fusicoccin (1 μ M ) had an inhibitory effect on ethylene and ACC production. Interestingly, fusicoccin (1 μ M ) had little or no effect on ACC-synthase promoted by high concentrations of IAA (1000 μ M ).
When BR and IAA were used in combination, fusicoccin inhibited ethylene and ACC production at concentrations as low as 0.05 μ M with maximum inhibition occurring at 0.5 μ M . At a 1 μ M concentration, fusicoccin was effective in inhibiting the synergistic stimulation of ACC-synthase promoted by BR and IAA.     

Effect of K+ and H+ stress and role of Ca2+ in the regulation of intracellular K+ concentration in mung bean roots

The effects of external K⁺, H⁺ and Ca2⁺ concentrations on the intracellular K+ concentration, [K⁺]i, and the K⁺-ATPase activity in 2-day-old mung bean roots [ Vigna mungo (L.) Hepper] were investigated. [K⁺]i, in mung bean roots was markedly decreased by external K⁺ or H⁺ stress and did not recover the initial value even after the stress was removed. This decrease in [K⁺]i, gradually disappeared with the addition of (Ca2⁺. Ca2⁺ may offset the harmful effects of ion stress. Ca2⁺ seems to have two effects on K+ transport; control of K⁺ permeability and activation of K⁺ uptake, although K⁺-ATPase activity was inhibited by Ca2⁺ concentrations higher than 10–4 M. We suggest that Ca2⁺ activates K⁺ uptake indirectly through the acidification of the cytoplasm.     

Effects of exogenously applied growth regulators on shoot growth of inbred lines of Plantago major differing in relative growth rate: differential response to gibberellic acid and (2-chloroethyl)-trimethyl-ammonium chloride

The possibility of modulating shoot growth charaeteristics of seedlings of two inbred lines of Plantago major L., differing in relative growth rate (RGR), by exogenously applied 6-benzylaminopurine (BA), α-naphthalene acetic acid (NAA), (gibberellic acid (GA₃) and (2-chloroethyl)-trimethyl-ammonium chloride (CCC) was investigated. BA completely inhibited growth of the shoot at a concentration of 1 m M , while lower concentrations had no effect. NAA reduced growth of the shoot at 10 ü M , while 1 m M completely inhibited growth. Addition of 10 μ M GA₃ or higher stimulated shoot fresh weight up to 20% and leaf area up to 30% for the slow growing inbred line (W9), but less for the fast growing line (A4). Application of 1 m M CCC, an inhibitor of gibberellin metabolism, reduced growth of both inbred lines, but to a larger extent in the fast growing seedlings.
The lower shoot growth of W9 was associated with a lower specific leaf area (SLA) and a higher dry matter percentage of the shoot, as compared with A4. NAA reduced growth by reducing SLA and increasing leaf thickness, but the percentage dry matter of the leaves was unaffected. Stimulation of the shoot growth by GA₃ application was associated with higher SLA and lower dry matter percentage. Application of CCC had opposite effects on SLA and dry matter percentage as compared with GA₃. GA seems to be involved in the regulation of at least part of the genetic difference in RGR in Plantago major .     

Xylogliicae- and cello-oligosaccharides: Antagonists of the growth-promoting effect of H+

Xyloglucan-oligosaccharides and cello-oligosaccharides, both of which are potential products of the action of cellulase on plant cell wail polysaccharides, inhibited acid-induced elongation in pea ( Pisum sativum L. cv. Alaska) stem segments. Xyloglucan-derived nonasaccharide (XG9; Glc₄-Xyl₃)Gal-Fuc) and decasaccharide (XG10; Glc₄-Xyl₃-Gal₂-Fue) inhibited acid-induced growth at 1.0 and 0.1 n M , respectively, whereas the heptasaccharide (XG7; Glc₄-Xyl₃) and octasaccharide (XG8; Glc₄-Xyl₃-Gal)₂ which lack L-fucose, did not. XG9 at 1 n M inhibited acid-induced growth as effectively as it inhibits auxin-induced elongation. This suggests that XG9's effect as an inhibitor of auxin action is not mediated by a suppresion of H⁺-efflux, but rather that XG9 blocks some step that is common to the action of both auxin and H⁺ on growth. Cello-oligosaccharides (degree of polymerisation 4–7) also inhibited acid-induced growth at 10 n M ; these are therefore a new class of possible oligosaccha-rin. The inhibitory effect of xyloglucan- and cellooligosaccharides on acid-induced growth was rapidly reversed by washing.