The effect of plant growth regulator treatments on the levels of ethylene emanating from excised turgid and wilted wheat leaves

Abscisic acid (ABA) inhibits the production of ethylene induced by water stress in excised wheat leaves and counteracts the stimulatory effect of 6-benzyladenine (BA) on this process. The stimulatory effect of BA and the inhibitory effect of ABA were equally pronounced whether external or endogenous ethylene levels were determined. When leaves were sprayed or floated on solutions of BA, indole-3-acetic acid (IAA), gibberellic acid (GA₃), or ABA, the relative activities of these growth regulators on stress-induced ethylene at 10^-4 mol l^-1 were BA>IAA >GA₃>controls>ABA. In non-stressed leaves, however, where the levels of ethylene produced were 2–20 times smaller, the relative activities were IAA >BA>GA₃>controls>ABA. The effects of BA and ABA spray treatment on water stress induced ethylene were closely similar whether the solutions were applied 2 or 18 h prior to the initiation of water stress. The relationships between the levels of endogenous growth regulators in the plant and ethylene release induced by water stress are discussed.Abbreviations BA 6-benzyladenine - IAA indole-3-acetic acid - GA₃ gibberellic acid - ABA abscisic acid - GLC gas-liquid chromatography - _leaf leaf water potential     

Phytohormone effects on hydrolytic activity of phosphohydrolases in red beet (Beta vulgaris L.) tonoplasts

The effects of indole-3-acetic acid (IAA), abscisic acid (ABA), gibberellic acid (GA₃) and kinetin on the hydrolytic activity of proton pumps (adenosine triphosphatase, H⁺-ATPase, pyrophosphatase, H⁺-PPase) of tonoplasts isolated from stored red beet (Beta vulgaris L. cv. Bordo) roots were studied. Results suggest that the phytohormones can regulate the hydrolytic activities of H⁺-ATPase and H⁺-PPase of the vacuolar membrane. Each of the proton pumps of the tonoplast has its own regulators in spite of similar localization and functions. IAA and kinetin seem to be regulators of the hydrolytic activity for H⁺-PPase whereas for H⁺-ATPase it may be GA₃. Stimulation of enzyme activity by all hormones occurred at concentrations of 10^–6 to 10^–7 M.Abbreviations IAA indole-3-acetic acid - ABA abscisic acid - GA₃ gibberellic acid - H⁺-ATPase adenosine triphosphatase - H⁺-PPase pyrophosphatase - ATP adenosine triphosphate - Tris Tris (hydroxymethyl)-aminomethane - MES (2[N-Morpholino]) ethane sulfonic acid - EDTA ethylene diamine tetraacetic acid - P_i inorganic phosphate     

Activity of Various Growth Substances in the Avena First Internode Test

The elongation growth of the Avena first internode segments was studied in the presence of one or several of the following growth substances: indoleacetic acid (IAA), 6-fur-furylamino purine (FAP, kinetin), 6-benzylamino purine (BAP), gibberellin A₃ (GA₃) and A₄₊₇ (GA₄₊₇), and abscisic acid (ABA). The cytokinins at concentrations of 10^?7 to 10^?6M stimulated growth with 4 to 6 per cent but this effect was not statistically significant. Concentrations higher than 5 × 10^?6M inhibited growth. FAP and BAP (from 10^?8M to 10^?6M) had no significant interaction with any other growth substance used. The two-factor interactions of IAA × ABA, IAA × GA₃, and GA₃× ABA, as well as the three-factor interaction IAA × ABA × GA₃ were significant. However, the IAA × ABA interaction was significant only when high concentration (10^?6M) of ABA was used. The growth inhibition produced by 10^?7 and 10^?6M ABA was overcome by about equimolar concentrations of IAA. The stimulation of growth by GA₃ and GA₄₊₇ (10^?9 to 10^?7M) was prevented by simultaneous application of ABA, and it was reduced significantly by application of IAA (10^?7 to 10^?8M). GA3 at 10^?8M combined with different concentrations of IAA gave slightly higher elongation than IAA alone but the observed values were significantly lower than expected assuming independent additive action.     

Abscisic acid and apical dominance in Phaseolus coccineus L.

Abscisic acid (ABA) in lanolin, applied to the internode of decapitated runner bean plants enhances the outgrowth of lateral buds. The optimum concentration of the paste is 10^-5 M. The effect of ABA is counteracted by indoleacetic acid (IAA) but not by gibberellic acid (GA₃). There is no effect when ABA is applied to the apical bud or lateral buds of intact plants. However, 13.2 ng given to the lateral buds of decapitated plants stimulate their growth, whereas higher concentrations are inhibitory. Consequently, ABA enhances growth of lateral buds directly, but only when apical dominance is already weakened. The growth of the decapitated 2^nd internode was not affected by ABA. Radioactivity from [2-¹⁴C] ABA, applied to nonelongating 2^nd internode stumps of decapitated runner bean plants moves to the lateral buds, whereas [1-¹⁴C]IAA-and [³H]GA₁-translocation is much weaker. ABA transport is inhibited if IAA or [³H]GA₁ is applied simultaneously. In elongating internodes [¹⁴C]ABA is almost completely immobile. [¹⁴C]IAA-and [³H]GA₁-translocation is not affected by ABA. The amount of radioactivity from labelled ABA, translocated to the lateral buds, is highest during the early stages of bud outgrowth.Abbreviations ABA 2,4-cis, trans-(+)-abscisic acid - GA gibberellic acid - IAA indoleacetic acid - p.l. plain lanolin     

Fibre length and gibberellins A1 and A20 are decreased in Eucalyptus globules by acylcyclohexanedione injected into the stem

Trinexapacethyl (TriEt), an acylcyclohexanedionetype inhibitor of gibberellin (GA) biosynthesis, was applied to 3-year-old Eucalyptus globules saplings by localised injection near the base of each stem. The objective was to alter cambial region GA levels and to study the effects on secondary xylem fibre development. Seven weeks later wood samples, with bark and cambial region intact, were removed 10 and 30 cm above the point of injection. Fusiform cambial cell dimensions were compared with those of fibre-tracheids in the most recently formed 100 um of secondary xylem. Increasing TriEt applications from 5 to 5 000 mg active ingredient significantly reduced average fibre length, and to a lesser extent average fusiform cambial cell length. Also reduced was the number of cells in the cambial zone and the number of differentiating fibres with primary walls. However, no trends were evident for changes in fibre diameter, the proportion of vessel elements or the ratio of cambial ray cells to fusiform cambial cells. Two gibberellins (GA₁ and GA₂₀), indole-3-acetic acid (IAA) and abscisic acid (ABA) were quantified in cambial region tissues by gas chromatographymass spectrometry using stable isotope labelled internal standards. Increasing TriEt application reduced both GA₁ and GA₂₀ levels. Effects on IAA and ABA were not significant, although their levels tended to be lower at the highest TriEt application rate. The elongation of secondary xylem fibres was positively correlated with higher levels of endogenous GA₁ (r_s= 0.74, P < 0.01) and GA₂₀ (r_s= 0.72, P < 0.01). These results support a causal role for GA₁ in cambial cell division. They are also consistent with the hypothesis that the elongation of differentiating secondary xylem fibres in woody an–giosperms is dependent on GA₁ levels in the cambial region.     

Long-term effects of plant hormones on K+ levels and transport in young wheat plants of different K+ status

Long-term effects of 1-naphtaleneacetic acid (NAA), benzyladenine (BA), gibberellic acid (GA₃), abscisic acid (ABA) and ethylene on K⁺ levels, K⁺ uptake and translocation to the shoot were studied in young wheat plants (Triticum aesticum L. cv. Martonvásári-8) grown at different K⁺ supplies. Na⁺ levels and K⁺/Na⁺ selectivity were also investigated. Both in shoots and roots, NAA, BA and ABA decreased K⁺ and Na⁺ levels more effectively in high-K⁺ plants than in low-K⁺ plants. GA, and ethylene did not influence K⁺ and Na⁺ levels. K⁺/Na⁺ selectivity in roots of low-K⁺ plants was increased in favour of K⁺ by BA, NAA and to a lesser extent by ABA. In high-K⁺ plants only BA increased the K⁺/Na⁺ ratio, whereas the effects of the other hormones were the opposite (NAA) or less pronounced (ABA). K⁺(⁸⁶Rb) uptake was inhibited by NAA and BA in low-K⁺ plants but not in high-K⁺ plants. K⁺(⁸⁶Rb) uptake was inhibited throughout by 10 μM ABA. K⁺(⁸⁶Rb) translocation to the shoot was influenced by the hormones similarly to the uptake patterns, with the exception of ABA, which inhibited translocation in low-K⁺ plants but not in high-K⁺ plants. The results show that hormonal effects may quantitatively and qualitatively be modified by K⁺ levels in the plant and that internal K⁺ concentration may play a role in the mechanisms regulating the effects of NAA, BA and ABA but probably not in those of GA₃ or ethylene.     

The effect of plant growth regulators on growth, morphology and condensed tannin accumulation in transformed root cultures of Lotus corniculatus

This study concerns the effects of four different classes of plant growth regulators on root morphology, patterns of growth and condensed tannin accumulation in transgenic root cultures of Lotus corniculatus L. (Bird's-foot trefoil). Growth of transformed roots in 2,4-dichlorophenoxyacetic acid (2,4-D) resulted in decreased tannin levels relative to controls at concentrations of 10^-6 M and above, while gibberellic acid (GA₃) inhibited tannin accumulation at concentrations of 10^-7 M and above. Benzyladenine (BA) had little effect at low concentrations (10^-7 M and below) but resulted in an increase in tannin levels at 10^-6 M. Abscisic acid had little effect on levels of condensed tannins at any of the concentrations used. Experiments involving growth regulator addition and medium transfer demonstrated that 2,4-D inhibition of tannin accumulation could be reversed by GA₃ and BA, while GA₃ downregulation could only be reversed by the addition of 2,4-D. Although 2,4-D inhibited tannin accumulation, addition of 2,4-D to root cultures grown for 14 or 28 days in the absence of plant growth regulators stimulated both growth and tannin biosynthesis. Characteristic alterations in root morphologies accompanied growth regulator-mediated modulation of tannin biosynthesis. Growth in 2,4-D resulted in partially de-differentiated root cultures while growth in GA₃ produced roots with an elongated phenotype. Restoration of tannin biosynthesis in 2,4-D-treated roots was accompanied by root re-differentiation and the production of new lateral roots.Abbreviations ABA abscisic acid - BA benzyladenine - 2,4-d 2,4-dichlorophenoxyacetic acid - GA₃ gibberellic acid 3 - FW fresh weight     

Gibberellic acid induces cytoplasmic acidification in maize coleoptiles

Indole-3-acetic acid (IAA), fusicoccin and weak acids all lower the cytoplasmic pH (pH_i) and induce elongation growth of maize (Zea mays L.) coleoptiles. Gibberellic acid (GA₃) also induces elongation growth and we have used confocal laser scanning microscopy to study the effects of GA₃ on pH_i employing the pH-indicator dyes, 2,7-bis(2-carboxyethyl)-5-(and-6) carboxyfluorescein and carboxy-semi-naphthorhodafluor-1. We confirm that GA₃ induces growth significantly in light-grown but only slightly or not at all in dark-grown coleoptiles. The growth induced by IAA treatment was similar in light- and dark-grown coleoptiles. The pH_i decreased by up to 0.6 units during the first 7 min of GA₃ or IAA treatment of both light- and dark-grown coleoptiles. Gibberellic acid inhibited IAA-induced growth of dark-grown coleoptiles. Hence, in dark-grown coleoptiles GA₃ may activate either directly or indirectly reactions that interfere with the signalling pathway leading to elongation growth. The possible role of pH_i in growth is discussed.Abbreviations ABA abscisic acid - AM acetoxymethyl ester - BCECF 2,7-bis(2-carboxyethyl)-5-(and-6) carboxyfluorescein - [Ca²⁺]_i cytoplasmic free calcium - GA_(n) gibberellin A_(n) - GA₃ gibberellic acid - IAA indole-3-acetic acid - PGR plant growth regulator - pH_i cytoplasmic pH - Pipes piperazine-N,N-bis[2-ethanesulfonic acid] - Snarf-1 carboxy-semi-naphthorhodafluor-1 We thank Dr R. King (CSIRO, Canberra) for providing the GA₁ and T. Phillips for processing the photographic material. H.R. Irving was supported by an Australian Research Council Research Fellowship and the work was supported by an Australian Research Council grant.     

Effect of morphactin on certain plant growth substances in bean roots

The effect of morphactin (methyl-2-chloro-9-hydroxyfluorene-9-carboxylate) on the content of several plant growth substances in bean roots was determined. Beans (Phaseolus vulgaris L. cv. Spartan) were soaked in aqueous solutions of morphactin, 1 x 10^-4, 1 x 10^-5, and 1 x 10^-6M and grown in moist vermiculite. As controls were used beans grown in water-moistened vermiculite either intact or having the root tips removed (decapped). The roots, morphactin-treated, controls, and the decapped ones were analyzed for indol-3-yl acetic acid (IAA), indol-3-yl acrylic acid (IAcA), indol-3-yl pyruvic acid (IPyA), indol-3-yl lactic acid (1LA), abscisic acid (ABA), gibberellins GA₁, GA₃, GA₄, and GA₉ using gas-liquid chromatographic methods. Morphactin, while affecting the geotropical responses, changed also the growth substance content of roots. IAA, ABA, GA₁, and GA₉ contents decreased, IPyA, IAeA, GA₃, and GA₄ contents were not affected and ILA content increased slightly with increasing dosages of morphactin. Growth substance pattern of decapped roots resembled that of the roots treated with the highest dose, 1 x 10^-4M, of morphactin.     

Determination of plant growth substances in liquid endosperm of immature walnut (Juglans nigra) nuts by an ELISA technique

Plant growth substances (PGSs) were analysed in liquid endosperm of black walnut using HPLC and an ELISA procedure. Of all the PGSs studied, we show no GA₃, low levels of cytokinins (io⁶A, i⁶Ade, i⁶Ado) and ABA, and very high level of IAAAbbreviations ABA Abscisic acid: - Ade Adenine: - GA₃ Gibberellic acid: - IAA Indole-3-acetic acid: - i⁶Ade N⁶(²-1) adenine: - i⁶Ado N⁶(²-isopentenyl adenosine: - io⁶A Zeatin riboside:     

Improvement of in vitro propagation of apricot cultivar ‘Bebecou’

Factors affecting successful establishment in vitro, rapid proliferation and rooting of apricot cultivar ‘Bebecou’ were studied. Ethanol and NaOCl were applied in several combinations for disinfection; chilling, plant growth regulators BA, IAA and GA₃, antibiotics, different culture vessels and systems of subculture were evaluated for the optimization of shoot proliferation and the auxins NAA and IBA were assessed for root induction. The highest number of new microshoots/explant (18.7) was obtained in a culture medium supplemented with 2.2 μM BA+0.57 μM IAA after 300 h of chilling. The effect of GA₃ (11.4 μM) on shoot proliferation was positive in combination with 4.4 or 8.9 μM BA. Shoot length and productivity were highest at 2.2 μM BA+11.4 μM GA₃+0.57 μM IAA and at 2.2 μM BA+0.57 μM IAA, respectively and decreased as cytokinin concentration increased. The antibiotic ‘Na-cefotaxime’ had a minimal impact on shoot growth when used at the lowest concentration (250 mg l⁻¹). Subculture every 2 weeks in a medium supplemented with 2.2 μM BA and 0.57 μM IAA was more efficient for shoot induction than alternation of 20 days culture in a propagation medium supplemented with 2.2 μM BA and 10 days culture in an elongation medium supplemented with 1.1 μM BA and 5.71 μM IAA. The highest number of roots/shoot (8.1) was recorded at 19.6 μM IBA.     

Influence of growth regulator treatments on dry matter production,fruit abscission,and14C-assimilate partitioning in citrus

Experiments were performed to monitor (1) uptake and translocation of foliar-applied microdroplets of¹⁴C hormones and (2) effects of multiple growth regulator sprays on foliar and fruit growth variables and photosynthate partitioning in Valencia orange trees (Citrus sinensis (L.) Osbeck). The uptake of¹⁴C-sucrose,¹⁴C-paclobutrazol (PP333), and¹⁴C-napthaleneacetic acid (NAA) in 6-month-old greenhouse-grown trees exceeded that of¹⁴C-abscisic acid (ABA) and¹⁴C-benzyladenine (BA) 48 h after microdroplet application.¹⁴C-sucrose transport from the application site was much greater than any other source, especially¹⁴C-BA. In a second study, 2-year-old Valencia orange trees were maintained under field conditions and were sprayed to foliar runoff (3 × /week for 3 weeks) with BA, NAA, ABA, PP333, and gibberellic acid (GA₃) at 100 M during flowering and early fruit set. Select branches were then briefly exposed to¹⁴CO₂ and harvested 24 h later. Both GA₃ and BA sprays promoted foliar growth. BA also stimulated fruit growth, whereas GA₃ sharply increased fruit dry weight while fruit number decreased. BA and GA₃ enhanced¹⁴C assimilate export by the foliage to the developing fruit, and GA₃ was especially active in promoting fruit sink intensity (¹⁴C/dry wt). The other compounds (NAA, ABA, PP333) restricted foliar and fruit growth. They also inhibited transport of¹⁴C assimilate from the leaves to the fruit. Results indicate that foliar-applied growth regulators can influence source-sink relations in citrus early in reproductive development by manipulating photoassimilate production and partitioning.     

Regulation of Growth in Avena (Oat) Stem Segments by Gibberellic Acid and Abscisic Acid

The purpose of this study was to analyze the nature of the interaction between gibberellic acid (GA₃) and abscisic acid (ABA) in the regulation of growth in excised Avena (oat) stem segments. Growth, compared to sucrose controls, was inhibited by ABA in the range of 10^?4 to 10^?6M. GA₃-promoted growth was also inhibited by ABA in the same concentration range. A Lineweaver-Burk analysis of the interaction between GA₃ and ABA indicated that ABA acts in a non-competitive fashion with GA₃. This same result was obtained previously with GA₃-indoleacetic acid (IAA) and GA₃-kinetin interactions with Avena stem sections. Our results indicate that ABA can inhibit GA₃-promoted growth within physiological concentrations, and that it is probably acting at a different physiological site from that for GA₃.     

Plant regeneration from stem and petiole protoplasts of sweet potato (Ipomoea batatas) and its wild relative,I. lacunosa

A protoplast-to-plant regeneration system has been established for sweet potato (Ipomoea batatas (L.) Lam.) and its wild relative, I. lacunosa L. Viable protoplasts, isolated from preplasmolyzed stems and petioles of in vitro-grown plants, were cultured on liquid MS (Murashige & Skoog 1962) medium that supported cell division and colony formation. Embryogenic calli of sweet potato were induced on agar-solidified MS medium supplemented with 3% (w/v) sucrose, 50 mg l^-1 casamino acids, 0.2–0.5 mg l^-1 2,4-d, 1.0 mg l^-1 kinetin and 1.0 mg l^-1 ABA. On average, 3 plants were regenerated from a single sweet potato callus subcultured on semi-solid MS medium containing 3% (w/v) sucrose, 800 mg l^-1 glutamine, 2.0 mg l^-1 BA or 1.0 mg l^-1 kinetin and 1.0 mg l^-1 GA₃. Embryogenic calli of I. lacunosa L. were initiated on semi-solid MS medium containing 0.2–0.5 mg l^-1 IAA and 1.0–2.0 mg l^-1 BA. An average of 5 plants was regenerated from a single sweet potato callus subcultured on semi-solid MS medium containing 0.5 or 1.0 mg l^-1 GA₃.Abbreviations ABA abscisic acid - BA benzyladenine - 2,4-d 2,4-dichlorophenoxyacetic acid - GA₃ gibberellic acid - IAA indole acetic acid - MES 2-(N-morpholino)-ethane sulfonic acid - NAA -naphthaleneacetic acid     

Carbonic Anhydrase,Photosynthesis, and Seed Yield in Mustard Plants Treated with Phytohormones

The leaves of 30-d-old plants of Brassica juncea Czern & Coss cv. Varuna were sprayed with 10^–6 M aqueous solutions of indole-3-yl-acetic acid (IAA), gibberellic acid (GA₃), kinetin (KIN), and abscisic acid (ABA) or 10^–8 M of 28-homobrassinolide (HBR). All the phytohormones, except ABA, improved the vegetative growth and seed yield at harvest, compared with those sprayed with deionised water (control). HBR was most prominent in its effect, generating 32, 30, 36, 70, 25, and 29 % higher values for dry mass, chlorophyll content, carbonic anhydrase (E.C. 4.2.1.1) activity, and net photosynthetic rate in 60-d-old plants, pods per plant, and seed yield at harvest, over the control, respectively. The order of response to various hormones was HBR > GA₃ > IAA > KIN > control > ABA.     

Induction and stimulation of in vitro flowering of Pharbitis nil by cytokinin and gibberellin

The influence of BA, GA₃ and IAA applied successively onflower bud formation in shoot apices of Pharbitis nil hasbeen investigated. The shoot apices were isolated from seedlings cultivatedunder non-inductive continuous light and from seedlings exposed to asubinductive (12 h) dark period. BA and GA₃ introducedsuccessively into culture medium replaced the inductive night, causing theflowering of plantlets in completely non-inductive continuous light (optimalconcentration of BA – 10^–7–10^–6mol dm^–3, GA₃ –10^–7–10^–6 moldm^–3) and stimulated this process under thesubthresholdinduction. These hormones applied in reverse sequence (in the first placeGA₃, then BA) did not affect flowering of explants. IAA nullifiedthestimulating effect of BA and GA₃. The influence of phytohormones onflowering may result from the change of growth correlations within the shootapical meristem.     

Flowering of Chrysanthemum under non-inductive long days by gibberellins and N6-benzyladenine

Summary The flowering and inflorescence development of Chrysanthemum morifolium cv. Pink Champagne under non-inductive long days was promoted by exogenous application of GA₅, GA₃, GA₄+GA₇ or GA₉ in combination with the cytokinin, BA. The combination of BA and GA₅ was highly effective, BA and GA₃ moderately effective. Applications of the GAs alone or BA alone also resulted in some flowering, with GA₃ and GA₅ being most effective. In general, the effects of GA and BA were synergistic, and the concentration of both growth substances was a limiting factor with regard to the number of plants flowering under long days. Only the concentration of GA was a limiting factor for inflorescence development, however. Simultaneous application of indole-3-acetic acid reduced inflorescence development in most treatments. Development to the stage of anthesis was in no case effected.Abbreviations BA N⁶-benzyladenine - GA gibberellin - IAA indole-3-acetic acid This research was supported by National Research Council of Canada Grant No. 2585.     

Hormone Profiling by LC-QToF-MS/MS in Dormant <Emphasis Type="Italic">Macadamia integrifolia</Emphasis>: Correlations with Abnormal Vertical Growth

A method for analyzing multiple plant hormone groups in small samples with a complex matrix was developed to initiate a study of the physiology of abnormal vertical growth (AVG) in Macadamia integrifolia (cv. HAES344). Cytokinins (CKs), gibberellins (GAs), abscisic acid (ABA), and auxins were detected in xylem sap and apical and lateral buds using high-performance liquid chromatography quadrupole time-of-flight tandem mass spectrometry (LC-QToF-MS/MS). The extraction method separated compounds with high sensitivity in positive (CKs) and negative (ABA, auxins, GAs) modes of QToF-MS/MS. CK profiles differed in xylem sap and apical and lateral buds irrespective of AVG symptoms. Trans-zeatin riboside (t-ZR) was dominant in sap of normal and AVG trees (∼4 and 6 pmol g⁻¹ FW, respectively). In apical buds isopentenyl adenine (iP) (∼30 pmol g⁻¹ FW) was the most abundant CK, and in lateral buds trans-zeatin (t-Z) (22–24 pmol g⁻¹ FW) and iP (24–30 pmol g⁻¹ FW) were the most abundant. t-Z levels of AVG trees were higher in apical buds (13.88 vs. 6.6 pmol g⁻¹ FW, p < 0.05) and lower in sap (0.16 vs. 0.51 pmol ml⁻¹, p < 0.005) compared to normal trees. ABA in lateral buds was 1.9 times higher (p < 0.001) in AVG. IAA was below quantification, whereas indole-3-butyric acid (IBA) was consistently present. GA₇ was the dominant GA in apical and lateral buds of all trees (100–150 pmol g⁻¹ FW). GA_{3, 4, & 9} were consistently present at low concentrations (<12 pmol g⁻¹ FW) in buds. GAs_{1, 3, & 9} were detected in xylem sap at low concentrations (<0.5 pmol g⁻¹ FW). Differences in sap amino acids (AA) were also assessed. In sap from AVG trees, asparagine and glutamine increased significantly (p < 0.05) in their contribution to total AA. Potential AVG hormone correlations are discussed.     

Effect of laterally applied gibberellin A4/7 on cambial growth and the level of indole-3-acetic acid in Pinus sylvestris shoots

Gibberellin A_4/7 (GA_4/7) was applied in lanolin or ethanol around the circumference at the midpoint of the previous-year terminal of dormant Pinus sylvestris seedlings. After cultivating the seedlings under environmental conditions favorable for growth for up to 10 weeks, cambial growth was measured as the radial widths of xylem and phloem, and the level of indole-3-acetic acid (IAA) was determined by combined gas chromatography-mass spectrometry using [¹³₆](IAA) as the internal standard. In intact seedlings, both 1 mg GA_4/7 g^?1 lanolin and 50 mg GA_4/7 I^?1 ethanol increased phloem production and the cambial region IAA level in the current-year terminal, without significantly altering its longitudinal growth. In the previous-year terminal, 1 mg GA_4/7 g^?1 lanolin promoted phloem production at the application point and increased the cambial region IAA level above this point, whereas 50 mg GA_4/7 I^?1 ethanol stimulated the production of both xylem and phloem at the treatment site and elevated the cambial region IAA level beneath it. Laterally applied GA_4/7 at 50 mg I^?1 ethanol stimulated xylem and phloem production in debudded previous-year terminals treated at the apical cut surface with 1 mg IAA g^?1 lanolin, but not in those treated with plain lanolin. However, the promotion of cambial growth in debudded terminals treated apically with 1 mg IAA g^?1 lanolin and laterally with 50 mg GA_4/7 I^?1 ethanol was not associated with an elevated IAA content in the cambial region. The results indicate that exogenous GA_4/7 can promote xylem and phloem production provided an IAA source is present, and that it or a metabolic product acts directly, rather than indirectly by stimulating longitudinal growth and/or raising the cambial region IAA level.     

Influence of gibberellic and abscisic acids and the growth retardant,CCC, upon plastid development

Summary Gibberellic acid (GA₃) enhances ultrastructural morphogenesis of plastids in greening cereals whilst abscisic acid (ABA) and CCC have the reverse effect over a shorter period. GA₃ application counteracts the ABA and CCC inhibition of membrane development and, over longer periods of greening, the fastest rate of chloroplast development is shown in the presence of both GA₃ and ABA. Experiments with isolated etioplasts show that the ABA inhibition of development also occurs and can be counteracted with GA₃ treatment but no individual enhancement of plastid morphogenesis by GA₃ was detected.Ribulose 1,5-diphosphate carboxylase (RuDPC) acitvity was also increased with applications of GA₃ and reduced with ABA treatment. The initial levels of RuDPC activity in the presence of CCC were concentration dependant; high in 10^-3 M CCC and low in 10^-6 M CCC but activity returned to normal levels after CCC application was stopped. Experiments with isolated etio-chloroplasts gave similar results but levels of RuDPC activity declined rapidly in both illuminated and un-illuminated incubated suspensions of intact etioplasts.