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.     

Effects of Abscisic Acid on Phenolic Content and Lignin Biosynthesis in Tobacco Tissue Culture

A significant depression of callus growth resulted from low concentrations of abscisic acid (ABA) added to the medium recommended by Linsmaier and Skoog. Low concentrations also decreased the chlorogenic acid and lignin content of the callus, and generally decreased amounts of scopolin and scopoletin in the tissue. Gibberellic acid (GA₃) stimulated callus growth in a low concentration (0.1 mg/1) and inhibited growth at a high concentration (10.0 mg/1). Both levels of GA₃ increased scopoletin accumulation in tobacco callus. A high concentration of GA₃ increased the accumulation of scopolin and chlorogenic acids, whereas a low concentration decreased the amounts of these two phenolic compounds. In comparison with the control, lignin synthesis was stimulated by a low GA₃ concentration, but a high GA₃ concentration did not have a significant effect. Both low and high concentrations of GA₃ overcame ABA inhibition of growth and lignin synthesis, and partially reversed ABA inhibition of scopoletin production. However, GA₃ did not reverse the inhibitory effect of ABA on scopolin production. The low concentration of GA₃ overcame the inhibition of chlorogenic acid production resulting from a 0.01 mg/1 concentration of ABA, but this was the only reversal of chlorogenic acid inhibition resulting from addition of GA₃ to the medium.     

In vitro propagation of the medicinal herbs Ocimum americanum L. syn. O. canum Sims. (hoary basil) and Ocimum sanctum L. (holy basil)

A procedure is outlined for in vitro propagation of two medicinal herbs, Ocimum americanum L. syn. O. canum Sims (hoary basil) and Ocimum sanctum L. (holy basil), using axillary shoot buds. Multiple shoot formation was induced from shoot bud explants of both species on Murashige and Skoog medium (MS) supplemented with benzyladenine (BA). The optimum BA concentrations for shoot proliferation were 0.25 mg/l for O. americanum and 1.0 mg/l for O. sanctum. Incorporation of 0.5 mg/l gibberellic acid (GA₃) along with BA in the culture medium resulted in a marked increase in the frequency of axillary branching as well as multiple shoot formation. Shoot buds collected between September through December were most responsive in culture. Shoots of O. americanum were rooted on half-strength MS supplemented with 1.0 mg/l indole-3-butyric acid (IBA), whereas O. sanctum rooted best on medium with 1.0 mg/l naphthaleneacetic acid (NAA). The plantlets were hardened off and successfully established in natural soil, where they grew and matured normally.Abbreviations BA N⁶-benzyladenine - 2,4-D 2,4-dichlorophenoxyacetic acid - GA₃ gibberellic acid - IAA indole-3-acetic acid - IBA indole-3-butyric acid - MS Murashige and Skoog (1962) medium - NAA 1-naphthaleneacetic acid     

Culture of Shoot Apices of Theobroma cacao

Surface sterilized buds of young cocoa plants (Theobroma cacao L.) taken at particular stages of the flush cycle were placed in Linsmaier and Skoog agar medium supplemented with a range of growth regulators. Only buds taken at the 1–2 (dormant) stage of the flush cycle and treated with gibberellic acid (GA₃) alone and GA₃plus kinetin (KN) supplement showed bud opening. In liquid Linsmaier and Skoog medium buds isolated at the 1–2 stage also responded to GA₃ and KN. In this case addition of KN caused bud opening, while GA₃ either initiated bud opening only or opening followed by leaf expansion depending on the concentration of GA₃ supplied. Bud development was inhibited when ABA was included in the medium hut this was overcome by the presence of GA₃ but not KN. Since a hormonal supplement was required for any response from the excised buds, it is suggested that the intermittent growth of the shoot apex in the intact plant may be determined by hormonal stimuli derived from other parts of the plant. The findings also indicate that the bud apices could be maintained in culture for long periods which may provide a basis for the development of a micropropagation procedure for cocoa.     

Der Einfluß von Wachstumsregulatoren auf Protein- und Enzym-Spektren kultivierter Explantate aus Rüben von Cichorium intybus L.

Summary On a simple nutrient medium in explants from roots of Cichorium intybus form shoots visible after about 14 days. Gibberellic acid (GA₃) does not influence the spontaneous development of the chicory explants. GA₃ in combination with kinetin inhibits shoot formation whereas kinetin alone promotes the process. On the other hand high concentrations of IAA inhibit the regeneration of shoots.The soluble proteins of chicory cultures treated with growth regulators were examined by disc-electrophoresis. It was shown that the proteins detected by staining with Amido black, phosphatases, esterases and glutamate dehydrogenase (GDH) present in the original root tissue remained constant under the different culture conditions during a period of 12 days. The quantitative changes of some of the proteins, phosphatases and esterases observed during the culture period were identical for all the different cultures in spite of the different morphogenetic behaviour. Only the activities of GDH and peroxidase changed after treatment with different growth regulators; however, in these cases, there was also no direct connection with the morphogenetic responses of the cultures.The specific activity of the GDH-band was promoted by IAA and at the same time the formation of peroxidases was inhibited. Kinetin delayed the formation of peroxidases during the first days of the culture period but promoted it later on. There was a repression by IAA of a specific kationic peroxidase. In the tissues treated with GA₃ the activity of peroxidases was always higher than in the control tissue. This effect of GA₃ can be partly explained by the fact that GA₃ inhibits the release of peroxidases of the explants into the nutrient medium.     

The Selective Effect of Abscisic Acid on Ribonucleic Acid Components

As determined by methylated albumin kieselguhr (MAK) fractionation, GA₃ (gibberellic acid) significantly increased and ABA (abscisic acid) decreased RNA levels. In the case of ABA this effect was selective, the ribosomal RNA manifesting the typical decrease; while the sRNA peak was markedly increased. The pattern of labelled uridine incorporation into RNA resembles the MAK absorbancy profile and here as well, ABA although causing an overall decrease, increases labelling in the sRNA peak. The results are interpreted as a possible selective effect of ABA or alternatively as an accumulation in the sRNA peak of rRNA breakdown products. From in vitro experiments it was furthermore evident that ABA mediated RNA hydrolysis probably does not involve a direct activation of RNase by ABA. The in vivo effect would probably be devious.     

The Role of Gibberellin, Abscisic Acid, and Sucrose in the Regulation of Potato Tuber Formation in Vitro

The effects of plant hormones and sucrose (Suc) on potato (Solanum tuberosum L.) tuberization were studied using in vitro cultured single-node cuttings. Tuber-inducing (high Suc) and -noninducing (low Suc or high Suc plus gibberellin [GA]) media were tested. Tuberization frequencies, tuber widths, and stolon lengths were measured during successive stages of development. Endogenous GAs and abscisic acid (ABA) were identified and quantified by high-performance liquid chromatography and gas chromatography-mass spectrometry. Exogenous GA_4/7 promoted stolon elongation and inhibited tuber formation, whereas exogenous ABA stimulated tuberization and reduced stolon length. Indoleacetic acid-containing media severely inhibited elongation of stolons and smaller sessile tubers were formed. Exogenous cytokinins did not affect stolon elongation and tuber formation. Endogenous GA₁ level was high during stolon elongation and decreased when stolon tips started to swell under inducing conditions, whereas it remained high under noninducing conditions. GA₁ levels were negatively correlated with Suc concentration in the medium. We conclude that GA₁ is likely to be the active GA during tuber formation. Endogenous ABA levels decreased during stolon and tuber development, and ABA levels were similar under inducing and noninducing conditions. Our results indicate that GA is a dominant regulator in tuber formation: ABA stimulates tuberization by counteracting GA, and Suc regulates tuber formation by influencing GA levels.     

Micropropagation of sweet viburnum (<Emphasis Type="Italic">Viburnum odoratissimum</Emphasis>)

A micropropagation protocol for shoot culture of sweet viburnum (Viburnum odoratissimum) is described. Nodal explants, initially established on MS medium, were transferred to WPM supplemented with combinations of BA and GA₃. Maximum shoot multiplication was observed on explants cultured on medium supplemented with BA concentration higher than 1.1 μM, and 14 μM GA₃. Although Stage II medium supplemented with BA concentration higher than 1.1 μM resulted in increased shoot multiplication, it also caused a decrease in shoot length. A negative carry over effect of GA₃ on rooting was observed in subsequent Stage III cultures. The presence of GA₃ in Stage II medium promoted shoot elongation, but it also caused a decrease in microcutting rooting. For this reason, 0.5 μM BA and 14 μM GA₃ were selected for optimum Stage II shoot multiplication. Although 100% microcuttings formed roots when cultured on medium containing 6.0 μM NAA, significant callus formation was observed and ex vitro survival rate was low (49%). Rooting was achieved after 3 weeks with 82% of microcuttings on medium supplemented with 3 μM IBA. The survival rate of plantlets under ex vitro conditions was 100% after 3 weeks. Plants looked healthy with no visually detectable phenotypic variation based on observation of about 30 plants.     

Interactions between Abscisic Acid, Gibberellins and Cytokinins in Grand Rapids Lettuce Seeds Germination

Experiments with Grand Rapids lettuce seeds (Lactuca sativa L.) maintained in darkness or irradiated with red light have shown that the inhibition of germination induced by low concentrations of ABA (2, 4, 6 μM) could be overcome by gibberellins (GA₃ or GA₄). The same results were obtained, although to a lesser extent, under the influence of two out of the four cytokinins tested (K and BAP) for seeds maintained in darkness. To suppress the block induced by higher concentrations of ABA (for example 8 μM), it was necessary to apply a cytokinin (K, BAP, Z or 2iP) and a gibberellin (GA₄ or GA₃) simultaneously, or a cytokinin following a red light treatment. Experiments conducted in darkness in which ABA (8 μM) was applied together with a cytokinin (BAP) and a gibberellin (GA₄) showed that the gibberellin and the cytokinin played similar roles towards each other and towards ABA.     

Calcium and calmodulin inhibitor effects on the growth of carrot (Daucus carota L.) and radish (Raphanus sativus L.) in nutrient culture

Growth of carrot and radish seedlings in nutrient culture was inhibited by pretreatment with three calmodulin inhibitors. There was little selective effect on specific organs, shoots, tap root and fibrous roots over a range of concentrations. Although pretreatment with CaCl₂ (0.5 mM) did not affect growth of untreated seedlings, it partially reduced the inhibitory effects of trifluoperazine over the concentration range 0.01–0.05 mM. Trifluoperazine reduced the growth of GA₃-treated seedlings but did not overcome the modifying effect of GA₃ in favouring shoot/root ratio; ABA exacerbated its inhibitory effect on overall seedling growth and particularly on tap root development.Abbreviations GA₃ gibberellic acid - ABA abscisic acid - CaCl₂ calcium chloride - GAs gibberellins - Tfp trifluoperazine     

Interactions of Abscisic Acid, Cytokinin and Gibberellin in the Control of Betacyanin Synthesis in Seedlings of Amaranthus caudatus

In de-rooted seedlings of Amaranthus caudatus L., betacyanin synthesis induced by white light or cytokinin was inhibited by abscisic acid (ABA) or a mixture of gibberellins A₄ and A₇ (GA_4/7). The GA_4/7 and ABA effects were additive. Thus ABA inhibited the cytokinin action but had no effect on the gibberellin response.     

Gibberellins and Abscisic Acid Promote Carbon Allocation in Roots and Berries of Grapevines

Carbon allocation within grapevines may affect berry growth and development. The plant hormones gibberellins (GAs) and abscisic acid (ABA) control various processes across the plant life and both have been involved in assimilate production and transport in different species. Hence, this work examined the distribution of sugars (sucrose, fructose, and glucose) and starch in grapevines at veraison after foliar applications of GA₃, ABA, and an inhibitor of GA biosynthesis, paclobutrazol (PBZ). The results demonstrated that GA₃ increased total grapevine mass, with carbon allocated to the whole grapevine (as structural and soluble carbohydrates). Both GA₃ and ABA increased monosaccharide (glucose and fructose) levels in berries (up to tenfold) and roots (up to threefold). However, GA₃ increased the net carbon fixation whereas ABA did not. PBZ diminished most growth parameters except grapevine mass, and allocated more carbohydrates to roots (up to threefold more sucrose and starch). Such results indicate that GAs promote net carbon fixation and transport, whereas ABA as a stress signal only enhances sugar transport; notwithstanding the two hormones promoted carbon allocation toward roots and berries.     

Micropropagation of <Emphasis Type="Italic">Pongamia pinnata</Emphasis> through enhanced axillary branching

A complete protocol is presented for the first time for the micropropagation of Pongamia pinnata, a biofuel tree, using cotyledonary nodes derived from axenic seedlings. Multiple shoots were induced in vitro from nodal segments through forced axillary branching. Murashige and Skoog (MS) medium supplemented with 7.5 μM benzylaminopurine (BAP) induced up to 6.8 shoots per node with an average shoot length of 0.67 cm in 12 d. Incorporation of 2.5 μM gibberellic acid (GA₃) in the medium during the first subculture after establishment and initiation of shoot buds significantly improved the shoot elongation. Single use of GA₃ during the first subculture eliminated the need for prolonged culturing on BAP medium. Further use of GA₃ in the medium was not useful. Shoot culture was established for at least two subcultures without loss of vigor by repeatedly subculturing the original cotyledonary node on shoot multiplication medium followed by shoot elongation medium after each harvest of the newly formed shoots. Thus, from a single cotyledonary node, about 16–18 shoots were obtained in 60 d. Shoots formed in vitro were rooted on full-strength MS medium supplemented with 1.0 μM indole butyric acid (IBA). Plantlets were successfully acclimated, established in soil, and transferred to the nursery.     

Effect of gibberellic acid combined with saponin on shoot elongation of Asparagus officinalis

Effect of gibberellic acid (GA₃) combined with saponin on shoot elongation of Asparagus officinalis was evaluated in tissue culture. Addition of saponin to GA₃ supplemented Murashige and Skoog (MS) basal medium showed a dose depended effect on shoot length of Asparagus officinalis. However, increasing concentration of saponin above 3.0 mg dm⁻³ decreased shoot length and showed yellowing and thinning of shoots. Saponin (3.0 mg dm⁻³) + GA₃ (0.2 mg dm⁻³) mixture treated by variable duration of sonication (0, 1, 3, 5, 7, 9, 11, 13 and 15 min) were evaluated for shoot elongation on MS basal medium. The highest shoot lengths (14.4 ± 0.3 and 15.1 ± 0.1 cm) were found after 5 and 7 min sonication.     

Effects of abscisic acid on the orientation and cold stability of cortical microtubules in epicotyl cells of the dwarf pea

Summary The effects of abscisic acid (ABA) on the orientation and cold stability of cortical microtubules (MTs) in epidermal cells of epicotyls of the dwarf pea,Pisum sativum L. cv. Little Marvel, were examined by immunofluorescence microscopy. The effect of ABA on the elongation of epicotyls and on the orientation of cortical MTs was opposite to that of gibberellin A₃ (GA₃). Treatment with ABA, which reduced the promotion of epicotyl elongation by GA₃, eliminated the GA₃-induced predominance of transverse MTs and resulted in a predominance of longitudinal MTs. The effect of ABA on the cold stability of cortical MTs was also opposite to that of GA₃. ABA increased the cold stability of MTs, while GA₃ decreased it. The predominance of longitudinal MTs brought about by ABA may have some relationship to ABA-induced inhibition of the elongation of the epicotyl. ABA may alter membrane proteins to stabilize cortical MTs and induce cold hardiness of plants.Abbreviations ABA abscisic acid - DMSO dimethylsulfoxide - FITC fluorescein isothiocyanate - GA₃ gibberellin A₃ - MT microtubule - PBS phosphate-buffered saline Dedicated to the memory of Professor Oswald Kiermayer     

Micropropagation of Salix pseudolasiogyne from nodal explants

The effect of phytohormones on the breaking of dormancy of axillary buds in Salix pseudolasiogyne and their subsequent proliferation from nodal explants were examined. Nodal explants obtained from a 20–year-old S. pseudolasiogyne tree were cultured either on woody plant basal medium (WPM) or WPM supplemented with benzyladenine (BA, 2.2/4.4 μM), zeatin (1.1/2.2 μM), gibberillic acid (GA₃, 2.9 and 14.5 μM), and GA₃ + BA (2.9 + 4.4 μM). Although axillary shoots developed in all the media, a higher percentage bud break occurred on BA supplemented media. To corroborate the results, endogenous levels of cytokinins [Cks, N ⁶-isopentenyladenine (iP), zeatin riboside (t-ZR), dihydrozeatinriboside (DHZR)] and abscisic acid (ABA) were determined. On BA supplemented media, the levels of zeatin type (Z-type) of Cks were higher than those of isopentenyladenine type of Ck in the explants, while the ABA level was low. Axillary shoots did not grow well and became necrotic upon subculture to fresh basal WPM. In order to improve shoot growth, they were subcultured twice at a 4-week interval on to WPM supplemented with BA (2.2/4.4 μM), GA₃ (1.4 μM), or GA₃ + BA (1.4 + 4.4/2.9 + 4.4 μM). Maximal shoot growth (93%) was achieved on WPM supplemented with 2.2 μM BA. Comparative analyses of endogenous Cks revealed that higher Cks (Z-type Cks) were present in actively growing shoots. Rooting was readily achieved when the shoots were subcultured to WPM without phytohormones. The rooted plants were acclimatized well upon transplantation.     

ABA and GA3 affect the growth and pigment composition in Andrographis paniculata Wall.ex Nees., an important folk herb

In this study, 5 μmol·L⁻¹ abscisic acid (ABA) and gibberellic acid (GA₃) were used to study the effect of both growth regulators on the morphological parameters and pigment composition of Andrographis paniculata. The growth regulators were applied by means of foliar spray during morning hours. ABA treatment inhibited the growth of the stem and internodal length when compared with control, whereas GA₃ treatment increased the plant height and internodal length. The total number of leaves per plant decreased in the ABA-treated plants, but GA₃ treatment increased the total number of leaves when compared with the control. Both growth regulators (ABA and GA₃) showed increased leaf area. ABA and GA₃ treatments slightly decreased the total root growth at all the stages of growth. The growth regulator treatments increased the whole plant fresh and dry weight at all stages of growth. ABA enhanced the fresh and dry weight to a larger extent when compared with GA₃. An increase in the total chlorophyll content was recorded in ABA and GA₃ treatments. The chlorophyll-a, chlorophyll-b, and carotenoids were increased by ABA and GA₃ treatments when compared with the control plants. The xanthophylls and anthocyanin content were increased with ABA and GA₃ treatments in A. paniculata plants.     

Effects of elevated carbon dioxide and/or ozone on endogenous plant hormones in the leaves of <Emphasis Type="Italic">Ginkgo biloba</Emphasis>

Four-year-old Gingko (Ginkgo biloba L.) trees were exposed to ambient and elevated concentrations of CO₂ and O₃, and their combination for 1 year, using open-top chambers in Shenyang, China in 2006. Growth parameters and endogenous plant hormones were measured simultaneously over the experiment period. Elevated CO₂ increased leaf area and leaf dry weight but had no effect on shoot length, increased indole-3-acetic acid (IAA), gibberellins A₃ (GA₃), zeatin riboside (ZR), dihydrozeatin (DHZR) and isopentenyl-adenosine (iPA) content but decreased abscisic acid (ABA) content. Elevated O₃ significantly decreased leaf area, leaf dry weight, shoot length, and decreased IAA, GA₃, ZR content but increased ABA content and had a little effect on iPA, DHZR content. Elevated CO₂ + O₃ decreased IAA, iPA and DHZR content while increased ABA and GA₃ content in the early stage of the exposure and then decreased in the late stage. The evidence from this study indicates that elevated CO₂ ameliorated the effects of elevated ozone on tree growth, and elevated CO₂ may have a largely positive impact on forest tree growth while elevated O₃ will likely have a negative impact.     

Distribution of Gibberellins and Abscisic Acid in Geotropically Stimulated Vicia faba Roots

The occurrence of gibberellins and abscisic acid (ABA) in extracts of roots of Vicia faba was demonstrated by gas-liquid chromatography (GLC) of the methylated eluates from the relevant zones of thin-layer chromatograms (TLC) of purified extracts. Quantitative determination of the hormone contents in extracts from upper and lower halves of roots which had been kept in the horizontal position for 30 min indicated a redistribution of the hormones during the geotropic stimulation. Gibberellins whose methyl esters appeared at the retention time of methylated gibberellic acid (GA₃), used as a standard, occurred in higher concentration in the upper than in the lower halves (ratio 2.08:1), whereas the concentration of ABA was highest in the lower halves (ratio 3.08:1). The ratio of the hormones in right and left halves of vertical roots was close to 1:1. Indoleacetic acid (IAA) and ABA were found to retard the elongation of roots of Vicia faba and Lepidium during the first 24 h. Additional experiments with Lepidium showed that this retardation occurs within the first hour after application. Low concentrations of GA₃, when applied to germinating seeds just after the radicles had broken the seed coat, stimulated root elongation in Vicia faba within 24 h and in Lepidium within 36 h. When applied to Lepidium seedlings with 20 mm long roots, GA₃ showed a stimulatory trend within the first 2 h, and distinct stimulation in the subsequent hours, particularly at the lowest concentrations, 0.01 and 0.001 mg/1. These results suggest the possibility of a participation of ABA and gibberellins (in addition to IAA) in the development of the positive geotropic curvature.