Efficient GA3-assisted plant regeneration from cell suspensions of three grape genotypes via somatic embryogenesis

Petioles from in vitro grown plants of interspecific grapevine hybrids cvs `Bianca', `Podarok Magaracha' and `Intervitis Magaracha' were cultured on solid NN medium supplemented with 2,4-D and BA at various concentrations. The callus developed was cultured in liquid NN medium supplemented with 0.5 mg l<sup>–1</sup> BA to induce formation of somatic embryos. Somatic embryos of globular and heart-stage developed in suspensions of `Podarok Magaracha' and `Intervitis Magaracha'. In contrast, `Bianca' did not undergo embryogenesis beyond globular stage. This made it necessary to perform subculture of the suspensions to HTE liquid medium supplemented with 0.2 mg l^–1 BA for the development of globular embryos into heart stage. Heart-stage embryos developed into torpedo-stage after subculturing suspensions of all three cultivars to liquid HTE medium supplemented with 0.1 mg l^–1 IAA and 30 mg l^–1 sodium hummate. Torpedo-stage embryo suspensions were subcultured in liquid HTE medium supplemented with 0.5 mg l^–1 BA, 0.5 mg l^–1 GA₃ and 0.5 mg l^–1 GA₃ + 0.2 mg l^–1 BA. After 12 days of incubation, plantlets were cultured on solid M2MS medium: without growth regulators and with 0.5 mg l^–1 BA. Plantlets that developed in liquid HTE media with 0.5 mg l^–1 GA₃ or 0.5 mg l^–1 GA₃ + 0.2 mg l^–1 BA produced 82–90% shoots on solid M2MS medium with 0.5 mg l^–1 BA after 50 days of culture.     

Plant regeneration from protoplasts isolated from callus ofGentiana crassicaulis

Fast growing calli induced from hypocotyl segments ofGentiana crassicaulis were used for preparation of protoplasts. High yields of viable protoplasts were produced in an enzyme solution containing 1–2% cellulase, I% pecfinase, and 0.5% Hemicellulase. Protoplasts were cultured in KM8P medium containing 1 mg/l 2,4-D, 0.5 mg/l 6BA, 500 mg/l LH, 0.5 M glucose and 0.1 M mannitol by the solid-liquid dual layer culture method. First division occurred within 4–5 days of culture at a frequency of 17.8%. Sustained divisions led to callus formation. Periodically diluting the cultures with freshly prepared liquid medium containing 1% glucose was critical for colony formation. Protocolonies about 2 mm in size were transferred onto MS medium supplemented with 3 mg/l ZT, 2 mg/l 6BA, 1 mg/l GA₃, 1 mg/l NAA and 6% sucrose to obtain embryogenic calli. Plantlets were regenerated via somatic embryogenesis at high frequency on hormone-free MS Medium.Abbreviations 6BA 6-benzylaminopurine - NAA naphthaleneacetic acid - 2,4-D 2,4 - dichlorophenoxyacetic acid - ZT zeatin - GA₃ gibberellic acid - LH lactalbumin hydrolysate - MES 2-(N-morpholino)-ethane sulfonic acid - MS Murashige & Skoog's medium(1962)     

Synergistic promotion of gibberellin and cytokinin on direct regeneration of floral buds from in vitro cultures of sepal segments in sinningia speciosa hiern

Summary This study reports the direct regeneration of flower buds from cultured sepal segments of Sinningia speciosa Hiern. Two types of floral bud regeneration were observed: regeneration of floral buds only (designed as B^F) and regeneration of both floral and vegetative buds (designed as B^F+V). The capacity of B^F regeneration was closely related to the location of sepal segments and the concentration of exogenous gibberellin (GA₃) and cytokinin in the medium. On the medium containing 1.0mgl^&#x2212;1 GA₃, the addition of 6-benzyladenine (BA) significantly increased the frequency of total flower bud (B^F+B^F+V) formation, with the frequency up to 91.5% in the presence of 0.4mgl^&#x2212;1 BA. On the medium containing 0.1mgl^&#x2212;1 BA, the addition of GA₃ also increased the frequency of total flower bud regeneration, with the frequency up to 74.3% in the presence of 1.0mgl^&#x2212;1 GA₃, but no further increase in regeneration was observed when the GA₃ concentration was higher than 1.0mgl^&#x2212;1. The capacity of B^F regeneration from different locations of sepal segments was differential. The adaxial part of sepal segments gave rise to the highest frequency of 56.7 and 84.3% for B^F and B^F+B^F+V, respectively.     

Somatic embryogenesis and plant regeneration in Quercus acutissima

Immature embryos of Quercus acutissima were collected weekly beginning 5 weeks post-fertilization and cultured on modified MS(Murashige and Skoog) medium containing 1,000 mg/l glutamine and 5 mM proline with different combinations of IBA(0.5–10.0 mg/l) and BA(0 or 1.0 mg/l) in light. The highest percentage of embryogenic cultures occurred on the medium containing 0.5 mg/l IBA or 1.0 mg/l BA and 0.5 mg/l IBA. Four weeks after initiation, the embryogenic cultures were transferred to MS medium without plant growth regulators and cultured for 4 weeks. The somatic embryos were then transferred to germination medium. The best germination results were achieved from WPM(Woody Plant Medium) containing 0.1 mg/l BA. Plantlets from somatic embryos were incubated on WPM supplemented with 0.2 mg/l BA for 4 weeks and plantlets with well developed shoots and roots were transplanted to perlite and peat moss(11, v/v) mixtures and placed in a culture room. After being hardened off for 8 weeks, they were transferred outdoors where they grew.Abbreviation BA N⁶-benzyladenine - IBA indole-3-butyric acid - GA₃ gibberellic acid - ABA abscisic acid - MS Murashige & Skoog Medium - WPM Woody Plant medium     

Simplified clonal multiplication of mulberry using liquid shake culture

Organogenesis was induced in callus derived from mature zygotic embryos of six families of loblolly pine (Pinus taeda L.) within 24 weeks of culture. Elongation of adventitious buds was achieved on TE medium supplemented with 0.5 mg l⁻¹ indole-3-butyric acid (IBA) and 2 mg l⁻¹ 6-benzyladenine (BA). The most suitable medium for root formation proved to be TE medium supplemented with 0.1 mg l⁻¹ IBA, 1 mg l⁻¹ BA, and 0.5 mg l⁻¹ gibberellic acid (GA₃). One hundred and sixty-nine regenerated plantlets were transferred to a perlite:peatmoss:vermiculite (1:1:1) soil mixture, and 98 plantlets survived in the field. This revised version was published online in June 2006 with corrections to the Cover Date.     

Gibberellins and Heterosis in Maize : II. Response to Gibberellic Acid and Metabolism of [H]Gibberellin A(20)

Two maize inbreds, CM7 and CM49, and CM7 × CM49, their F₁ hybrid (which displayed significant heterosis), were examined with regard to response to exogenous gibberellin A₃ (GA₃), and in their ability to metabolize GA₂₀, a native GA of maize. The leaf sheath elongation response to GA₃ was far greater for the imbreds than for their hybrid. The inbreds also displayed significant elongation of the leaf blades in response to GA₃, whereas the hybrid was unaffected. Promotion of cell division in the leaf sheath of CM7 and the hybrid was effected by GA₃, but no promotion of cell elongation was observed in CM49, even though significant leaf sheath elongation occurred. Shoot dry weight of both inbreds was significantly increased by GA₃, but response by the hybrid in this parameter was slight and variable. Root dry weight of CM7 was significantly increased by GA₃, but was unchanged in CM49 and the hybrid. Thus, inbred shoot dry weight increases effected by GA₃ were not at the expense of the root system. Rapid metabolism of [2,3-³H]GA₂₀ occurred in all genotypes, although genotypic differences were observed. The hybrid had the highest rates of metabolism to GA glucosyl conjugate-like substances. Oxidative metabolism was also fastest in the hybrid, followed by CM7, and slowest in CM49, the slowest-growing inbred. Thus, rate of GA₂₀ metabolism is under genetic control in normal (i.e. not dwarfed) maize genotypes. These results, taken together with previous reports that the hybrid has significantly enhanced levels of endogenous GA-like substances, suggest that GA play a role in the expression of heterosis in maize.     

Effects of Growth Regulators on Direct Flowering of Isolated Ginseng Buds <Emphasis Type="Italic">in vitro</Emphasis>

An in vitro method for obtaining gingseng inflorescences directly from explants of gingseng (Panax ginseng) is reported. Isolated shoot-buds of somatic embryo-derived plantlets ginseng were used as explants and incubated in B5 medium supplemented with 1 mg l⁻¹ benzyladenine (BA) and 1 mg l⁻¹ gibberellic acid (GA₃). About 15% of the buds flowered directly without developing vegetative organs. Cytokinin was found to be the key factor for inducing these isolated buds to proliferate and flower, but both these processes also occurred when benzyladenine (BA) was replaced by thidiazuron (TDZ). The optimal concentration of TDZ for obtaining the best ratios of bud proliferation and total flowering was 0.1 mg l⁻¹, while the highest number of vegetative shoots was obtained in medium supplemented with 1 mg l⁻¹ GA₃ and 0.1 mg l⁻¹ TDZ. The explant elongated abnormally in the presence of 10 mg l⁻¹ GA₃. Although a low concentration (1 mg l⁻¹) of NAA increased the bud proliferation ratio in the medium supplemented with 0.1 mg l⁻¹ TDZ and 1 mg l⁻¹ GA₃, a high concentration (5 mg l⁻¹) of NAA reduced the bud proliferation ratio and inhibited the flowering.     

Differential cytokinin effects on the stimulation of in vitro shoot proliferation from meristematic explants of castor (Ricinus communis L.)

A highly efficient and reproducible method of in vitro propagation using meristematic explants has been developed for castor. Embryo axes and shoot tips were cultured on Murashige and Skoog (MS) medium supplemented with 0.5–10.0 mg/l of adenine, N⁶-benzyladenine (BA), kinetin (Kn), thiadiazuron (TDZ) and zeatin. TDZ (1.0–10.0 mg/l) gave the maximum number of shoots (37.8–40.0) from embryo axes, while BA (2.0 mg/l) was found superior to other cytokinins for obtaining the highest number of shoots (46.7) from the shoot apex. Adenine and Kn at all of the tested concentrations resulted in low proliferation rates from embryo axes. The carryover effect of the cytokinins was tested by subculturing proliferating shoot cultures from various media onto the medium fortified with 0.5 mg/l BA. There was no significant influence of the cytokinins on subsequent proliferation from the two explant types except for TDZ with embryo axes. The number of shoots from TDZ-habituated embryo axes ranged between 36.0 and 81.7, while it varied from 5.7 to 22.0 and 3.7 to 28.3 in axillary buds and embryo axes, respectively, on the other media. For elongation of shoots, gibberellic acid (GA₃) (0.1–1.0 mg/l) was added to the medium supplemented with 0.2–0.5 mg/l BA. Incorporation of GA₃ (0.1 mg/l) significantly enhanced the frequency of elongated shoots but drastically reduced the multiplication ability. Hence, proliferating shoot clusters were periodically transferred to the medium supplemented with 0.5 and 0.2 mg/l BA for further multiplication and elongation. Well-developed shoots were rooted on half-strength MS medium supplemented with 1.0 mg/l indole-3-butyric acid. The rooted plantlets were acclimatized with more than 60% success. Received: 17 June 1997 / Revision received: 3 September 1997 / Accepted: 20 September 1997     

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     

Micropropagation of globe artichoke (Cynara scolymus L.) from underground dormant buds (“ovoli”)

Summary Side shoots excised from underground dormant buds ofCynara scolymus L. were used as primary explants to establishin vitro cultures. A 3×3 factorial experiment with all possible combinations of three concentrations (0.5, 1.0, 2.0 mg/liter or 2.22, 4.44, 8.88 μM) ofN ⁶-benzyladenine (BA) and three concentrations (0, 0.1, 0.2 mg/liter or 0, 0.54, 1.07 μM) of 1-naphthaleneacetic acid (NAA) was used to determine the optimum growth regulator combination for shoot multiplication. The highest rate of axillary shoots was induced on Murashige and Skoog agar medium supplemented with 0 mg NAA/liter and 1.0 mg BA/liter (4.44 μM). Other cytokinins tested (kinetin, zeatin, and 2-isopentenyl-adenine were less effective than BA in inducing axillary shoot growth. Up to 60% of elongated microshoots rooted after 5 weeks on 1/2 MS agar medium supplemented with 2 mg/liter (11.42 μM) indole-3-acetic acid (IAA). Seventy percent of rooted plantlets were transferred successfully into soil. Plants are under evaluation for their genetic uniformity and clonal fidelity.     

Heterosis and the metabolism of gibberellin A20 in sorghum

The correlation between gibberellin (GA) metabolism and growth rate was investigated using two Sorghum bicolor inbred lines, Hegari and AT×623, and their heterotic F₁ hybrid. Previous studies have demonstrated that this hybrid is taller and has substantially greater shoot dry weights and leaf areas than either parental inbred. [³H]GA₂₀ was applied to the leaf whorl of seedlings and after 24 hours, plants were harvested and separated into roots, shoot cylinders containing the apical meristems, and leaf blades. Chromatographic analyses of metabolites indicated the conversions of [³H]GA₂₀ to [³H]GA_{1,8 and 29}. The conversion of [²H]GA₂₀ to [²H]GA₁ was demonstrated by gas chromatography-selected ion monitoring (GC-SIM). Putative glucosyl conjugates of all of the [³H]GAs were also produced and GA₈ was identified by GC-SIM following enzymic cleavage of the putative [³H]GA₈ glucosyl conjugate fraction. Comparing the genotypes, [³H]GA₂₀ metabolism was more rapid in the shoot cylinders of the hybrid than in the shoot cylinders from inbreds. In the hybrid samples, there was a three-fold increase in the putative conjugate(s) of [³H]GA₁ which was the principal metabolite, and increased production of [³H]GA₈ and the putative conjugates of [³H]GA₂₉ and [³H]GA₈. Conversely, levels of the remaining precursor, [³H]GA₂₀, and its putative conjugate(s) were reduced in the hybrid. The rate of GA₂₀ metabolism was thus positively correlated with growth rate across these sorghum genotypes. This correlation supports a promotive role of GA in the regulation of shoot growth and in the expression of heterosis (hybrid vigor) in sorghum.     

Micropropagation ofFagus sylvatica L.

Summary An in vitro shoot multiplication system was established from juvenileFagus sylvatica L. tissues, and plantlets were regenerated. Embryonic axes were excised from beech seeds and germinated in vitro on media supplemented with 6-benzyladenine (BA) to obtain plantlets with axillary shoots. Shoot multiplication was maintained by sequential subculture of axillary shoot tips and basal segments on Woody Plant Medium supplemented with 0.5 mg/liter BA+2 mg/liter zeatin+0.2 mg/liter naphthaleneacetic acid (NAA). The effeciency of shoot multiplication clearly depended on the kind of explant used. Transfer to fresh medium every 2 wk during the 6-wk multiplication cycle improved multiplication rates. In the rooting stage, an initial 7-day dark period significantly improved rooting capacity and accelerated the emergence of roots on auxin-treated shoots. Adventitious buds were induced on the intact hypocotyls of the whole plantlets derived from the initial embryonic axis explants, especially on those cultured on medium with 1 mg/liter BA. Cotyledon and hypocotyl segments isolated from seedlings grown in vitro from embryos also exhibited capacity for adventitious bud formation, especially when cultured on media supplemented with 0.5 mg/liter BA + 0.1 mg/liter NAA.     

Gibberellins Increase Cuticle Deposition in Developing Tomato Fruit

Effects of the gibberellins A₄₊₇(GA₄₊₇) and A₃(GA₃), benzyladenine (BA) and forchlorfenuron (CPPU) on deposition of the cuticular membrane (CM) in developing tomato (Lycopersicon esculentum L.) fruit were investigated. Growth regulators were applied when fruit development within trusses ranged from the flower to the mature stage. Developmental stage of fruit at the time of application was indexed by fruit diameter. Fruit were harvested at maturity, the CM isolated enzymatically on an individual fruit basis and mass of CM per unit fruit surface area calculated. In mature fruit, mass of CM per fruit increased with fruit size, but mass of CM per unit surface area was independent of fruit size, position within a truss and position of the truss on the plant. GA₄₊₇ and GA₃ increased CM mass per unit fruit surface area at concentrations up to 300 mg l⁻¹. Young fruit (5–10 mm diam. at time of application) was most responsive. Responsiveness decreased as fruit development at application progressed towards maturity. There was no consistent effect of GA₄₊₇ or GA₃ on fruit mass. BA (up to 100 mg l⁻¹) or CPPU (up to 3 mg l⁻¹) had no significant effect on CM mass per unit surface area regardless of developmental stage. Higher concentrations of BA or CPPU decreased CM mass per unit surface area. There was no effect of BA or CPPU on fruit mass. Potential mechanisms and benefits of a gibberellin induced increase in CM deposition are discussed.     

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     

Rapid propagation of lemongrass (Cymbopogon flexuosus (Nees) Wats.) through somatic embryogenesis in vitro

Somatic embryos induced from callus cultures of lemongrass [Cymbopogon flexuosus (Nees) Wats.] on Murashige and Skoog medium supplemented with 5 mg/l of 2,4-D, 0.1 mg/l of NAA and 0.5 mg/l of Kn developed into plantlets when plated on a medium supplemented with 3 mg/l of BA, 1 mg/l of GA₃ and 0.1 mg/l of NAA. The regeneration potential of callus was retained for more than 2 years on the nutrient medium supplemented with comparatively lower levels of growth regulators (2,4-D at 2 mg/l, NAA at 0.1 mg/l and Kn at 0.25 mg/l). Approximately 30–35 plantlets were produced after two months of culture per 100 mg of callus inoculated. Regenerants were transplanted into soil and transferred to the field for assessment of various morphological and biochemical characteristics. The results of 1 year of field trials showed that plants derived from somatic embryoids were more uniform in all the characteristics examined when compared with the field performance of plants raised through slips by standard propagation procedures. Thus, a procedure has been developed for high frequency long term plant production of lemongrass through in vitro methods.Abbreviations 2,4-D 2,4 -dichlorophenoxyacetic acid - NAA -naphthalene acetic acid - Kn kinetin - BA benzyladenine - GA₃ gibberllic acid - MS Murashige and Skoog (1962) basal medium     

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.     

In vitro shoot tip multiplication of cowpea Vigna unguiculata (L.) walp

Summary Shoot multiplication was induced in cowpea, cv. Georgia-21, from shoot tip explants. Shoot tips, 5 mm long, were isolated from in vitro-grown seedlings and cultured on MS medium containing N⁶-benzyladenine (BA) at 1, 2.5, or 5 mg/liter (4.4, 11.1, or 22.2 μM) or 6-furfurylaminopurine (kinetin) at 1, 2.5, or 5 mg/liter (4.6, 11.6, or 23.2 μM) combined with 2,4-dichlorophenoxyacetic acid (2,4-D) at 0.01, 0.1, or 0.5 mg/liter (0.05, 0.5, or 2.3 μM) or naphthaleneacetic acid (NAA) at 0.01, 0.1, or 0.5 mg/liter (0.05, 0.5, or 2.7 μM). Cultures were maintained at a 12-h photoperiod (40 μmol·m⁻²·s⁻¹) and 23 ± 2° C. Treatments with BA induced greater shoot proliferation than those with kinetin. The highest number of shoots was produced on 5 mg (22.2 μM) BA per liter in combination with NAA or 2,4-D at 0.01 mg/liter (0.05 μM). Callus proliferated from the basal ends of shoot pieces in all treatments. The cultures also formed roots in the presence of kinetin, but not on BA-containing medium. To produce whole plants, the shoots were separated and rooted on 0.1 mg (0.5 μM) NAA per liter. Resulting plants grew normally under greenhouse conditions. Shoot tips provide an excellent explant source for cowpea micropropagation and can be used for callus induction.     

Implication of Ethylene in the Release of Secondary Dormancy in Amaranthus caudatus L. Seeds by Gibberellins or Cytokinin

Ethephon (Eth), gibberellin A₃, A_{4 + 7} (GA₃, GA_{4 + 7}), and 6-benzyladenine (BA) removed secondary dormancy of Amaranthus caudatus seeds. The GAs and BA potentiated the effect of ethephon or 1-aminocyclopropane-1-carboxylic acid (ACC), an ethylene biosynthesis precursor, in terms of the rate or final percent of germination. Aminoethoxyvinylglycine (AVG), an ACC synthase activity inhibitor, was observed to simultaneously inhibit the release from dormancy effected by GA₃ or BA as well as the ethylene production stimulated by these regulators. Breaking of secondary dormancy by GA₃, GA_{4 + 7} or BA was prevented by 2,5-norbornadiene (NBD), an inhibitor of ethylene binding. Ethylene completely or markedly reversed the inhibitory effect of NBD. We thus conclude that the removal of secondary dormancy in Amaranthus caudatus seeds by gibberellin or benzyladenine involves ethylene biosynthesis and action.     

Gibberellin and CCC Effects on Flowering and Growth in the Long-day Plant Lemna gibba G3

The application of gibberellic acid (GA₃) to the non-rosette long-day plant Lemna gibba G3 at concentrations from 0.1 to 100 mg/l did not induce flowering on short days and inhibited flowering on long days at concentrations of 1 mg/l and higher. On both short and long days GA₃ concentrations above 1 mg/l caused a decrease in frond size and fresh and dry weight, but an increase in the rate of frond production and thus an increase in the # VF (number of vegetative fronds). Identical results were obtained when gibberellin A₇ was used instead of GA₃.     

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