Showing papers on "Gibberellic acid published in 2008"

The Gibberellic Acid Signaling Repressor RGL2 Inhibits Arabidopsis Seed Germination by Stimulating Abscisic Acid Synthesis and ABI5 Activity

Abstract: Seed germination is antagonistically controlled by the phytohormones gibberellic acid (GA) and abscisic acid (ABA). GA promotes seed germination by enhancing the proteasome-mediated destruction of RGL2 (for RGA-LIKE2), a key DELLA factor repressing germination. By contrast, ABA blocks germination by inducing ABI5 (for ABA-INSENSITIVE5), a basic domain/leucine zipper transcription factor repressing germination. Decreased GA synthesis leads to an increase in endogenous ABA levels through a stabilized RGL2, a process that may involve XERICO, a RING-H2 zinc finger factor promoting ABA synthesis. In turn, increased endogenous ABA synthesis is necessary to elevate not only ABI5 RNA and protein levels but also, critically, those of RGL2. Increased ABI5 protein is ultimately responsible for preventing seed germination when GA levels are reduced. However, overexpression of ABI5 was not sufficient to repress germination, as ABI5 activity requires phosphorylation. The endogenous ABI5 phosphorylation and inhibition of germination could be recapitulated by the addition of a SnRK2 protein kinase to the ABI5 overexpression line. In sleepy1 mutant seeds, RGL2 overaccumulates; germination of these seeds can occur under conditions that produce low ABI5 expression. These data support the notion that ABI5 acts as the final common repressor of germination in response to changes in ABA and GA levels.

Sucrose transporter StSUT4 from potato affects flowering, tuberization, and shade avoidance response

Abstract: Sucrose (Suc) transporters belong to a large gene family. The physiological role of SUT1 proteins has been intensively investigated in higher plants, whereas that of SUT4 proteins is so far unknown. All three known Suc transporters from potato (Solanum tuberosum), SUT1, SUT2, and SUT4, are colocalized and their RNA levels not only follow a diurnal rhythm, but also oscillate in constant light. Here, we examined the physiological effects of transgenic potato plants on RNA interference (RNAi)-inactivated StSUT4 expression. The phenotype of StSUT4-RNAi plants includes early flowering, higher tuber production, and reduced sensitivity toward light enriched in far-red wavelength (i.e. in canopy shade). Inhibition of StSUT4 led to tuber production of the strict photoperiodic potato subsp. andigena even under noninductive long-day conditions. Accumulation of soluble sugars and Suc efflux from leaves of transgenic plants are modified in StSUT4-RNAi plants, leading to modified Suc levels in sink organs. StSUT4 expression of wild-type plants is induced by gibberellins and ethephon, and external supply of gibberellic acid leads to even more pronounced differences between wild-type and StSUT4-RNAi plants regarding tuber yield and internode elongation, indicating a reciprocal regulation of StSUT4 and gibberellins.

A membrane-bound NAC transcription factor NTL8 regulates gibberellic acid-mediated salt signaling in Arabidopsis seed germination

Abstract: Gibberellic acid (GA) plays a key role in seed germination through coordinate interactions with other growth hormones and external signals. However, the way in which external signals are incorporated into the GA-signaling pathway is largely unknown. Here, we demonstrate that a membrane-bound NAC transcription factor NTL8 mediates the salt regulation of seed germination via the GA pathway, primarily independently of ABA. NTL8 is induced by high salinity. Its expression is also elevated by a GA biosynthetic inhibitor paclabutrazol (PAC), but is repressed by GA. Notably, high salinity greatly represses the GA3 oxidase 1 (GA3ox1) gene, supporting the hypothesis that salt signals inhibit seed germination by repressing GA biosynthesis. Induction of NTL8 and repression of GA3ox1 by high salinity still occur in the ABA-deficient aba3-1 mutant. Accordingly, the germination of a T-DNA insertional ntl8-1 mutant seed is resistant to high salinity and PAC. Interestingly, NTL8 is significantly induced during cold imbibition, but the induction declines quickly in germinating seeds, like RGL2. NTL8 activity is also regulated by controlled proteolytic release of the membrane-bound NTL8 form. Its release from the membranes is activated by PAC and high salinity. Our data support that NTL8 modulates GA-mediated salt signaling in regulating seed germination. This regulatory scheme may provide an adaptative fitness, which delays seed germination under high salinity conditions.

High-frequency plant regeneration from leaf-disc cultures of Jatropha curcas L.: an important biodiesel plant

Abstract: A simple, high-frequency and reproducible protocol for induction of adventitious shoot buds and plant regeneration from leaf-disc cultures of Jatropha curcas L. has been developed. Adventitious shoot buds were induced from very young leaf explants of in vitro germinated seedlings as well as mature field-grown plants cultured on Murashige and Skoog’s (MS) medium supplemented with thidiazuron (TDZ) (2.27 μM), 6-benzylaminopurine (BA) (2.22 μM) and indole-3-butyric acid (IBA) (0.49 μM). The presence of TDZ in the induction medium has greater influence on the induction of adventitious shoot buds, whereas BA in the absence of TDZ promoted callus induction rather than shoot buds. Induced shoot buds were multiplied and elongated into shoots following transfer to the MS medium supplemented with BA (4.44 μM), kinetin (Kn) (2.33 μM), indole-3-acetic acid (IAA) (1.43 μM), and gibberellic acid (GA3) (0.72 μM). Well-developed shoots were rooted on MS medium supplemented with IBA (0.5 μM) after 30 days. Regenerated plants after 2 months of acclimatization were successfully transferred to the field without visible morphological variation. This protocol might find use in mass production of true-to-type plants and in production of transgenic plants through Agrobacterium/biolistic-mediated transformation.

Extracts of the Brown Seaweed Ascophyllum nodosum Induce Gibberellic Acid (GA3)-independent Amylase Activity in Barley

Abstract: Extracts of the brown seaweed Ascophyllum nodosum have been used as a biostimulant to promote growth and productivity in a number of agricultural production systems. Although the extracts have been shown to improve seedling emergence and vigor in a variety of plants, including barley, the mechanism(s) of this growth-promoting effect is(are) largely unknown. In our study, A. nodosum extract induced amylase activity in barley seed-halves; a significant difference in amylase activity was observed in seeds without an embryo. The addition of activated charcoal to the treatment media negated the bioactivity of the extracts suggesting the organic nature of bioactive compounds in A. nodosum extracts. The extracts induced amylase activity in a gibberellic acid (GA)-deficient barley mutant (grd2). LC-MS-MS analysis failed to detect the presence of GA3 in the extracts. ABA supplementation of the medium caused a significant reduction of amylase activity in GA-treated seeds compared with those treated with the A. nodosum extract. Taken together, our results suggest that the organic components of A. nodosum extract induce amylase activity independent of GA3 and might act in concert with GA-dependent amylase production leading to enhanced germination and seedling vigor in barley. Being derived from a renewable resource, the bioactive compounds from A. nodosum could be used to improve crop productivity in sustainable agricultural systems.

Roles of gibberellins and abscisic acid in dormancy and germination of red bayberry (Myrica rubra) seeds.

Abstract: Intact seeds from freshly harvested fruits of Myrica rubra (Sieb et Zucc.) were dormant and required 8 weeks of warm stratification followed by 12 weeks of cold stratification for germination. Exogenous application of gibberellic acid (GA(3)) to intact fresh seeds was effective in breaking dormancy, with > 70% of seeds germinating when treated with 5.2 mM GA(3) and incubated at a day/night temperature of 30/20 degrees C for 20 weeks. Removing the hard endocarp or endocarp plus seed coat of fresh seeds promoted germination, and addition of GA(3) to the embryo accelerated germination. The gibberellins GA(1) and GA(4) were more effective than GA(3) in promoting germination of seeds with the endocarp removed. Endogenous contents of GA(1), GA(3), GA(4), GA(7) and GA(20) were quantified by gas chromatography-mass spectrometry-selected ion monitoring in the endocarps, seed coats and embryos of fresh seeds treated with 5.2 mM GA(3). The content of GA(3) decreased in the endocarp during incubation, whereas GA(1) contents increased in the endocarp and seed coat. A high GA(1) content was detected in the endocarps and embryos of newly germinated seeds. We speculate that GA(3) was converted to GA(1) during incubation and that GA(1) is involved in seed germination. Endogenous abscisic acid (ABA) contents were measured in fresh seeds and in warm and cold stratified seeds. The ABA content in fresh seeds was distributed in the order endocarp > seed coat > embryo, with the content in the endocarp being about 132-fold higher than in the seed coat and embryo. Total ABA content of seeds subjected to warm or cold stratification, or both, was 8.7- to 14.0-fold lower than that of fresh seeds. Low contents of endogenous GA(1), GA(3), GA(7) and GA(20), but elevated contents of GA(4), were found in the seed coats and endocarps of warm plus cold stratified seeds and in the seed coats and embryos of newly germinated seeds. These observations, coupled with the finding that GA stimulated germination of dormant Myrica seeds, provide evidence that endogenous ABA inhibited release of dormancy and that endogenous gibberellins, especially GA(4) or GA(1), or both, are involved in germination.

Analysis of embryonic proteome modulation by GA and ABA from germinating rice seeds.

Abstract: The phytohormones gibberellic acid (GA) and abscisic acid (ABA) play essential and often antagonistic roles in regulating plant growth, development, and stress responses. Using a proteomics-based approach, we examined the role of GA and ABA in the modulation of protein expression levels during seed germination. Rice seeds were treated with GA (200 microM), ABA (10 microM), ABA followed by GA, GA followed by ABA, and water as a control and then incubated for 3 days. The embryo was dissected from germinated seeds, and proteins were subjected to 2-DE. Approximately, 665 total protein spots were resolved in the 2-D gels. Among them, 16 proteins notably modulated by either GA or ABA were identified by MALDI-TOF MS. Northern analyses demonstrated that expression patterns of 13 of these 16 genes were consistent with those of the proteome analysis. Further examination of two proteins, rice isoflavone resuctase (OsIFR) and rice PR10 (OsPR10), using Western blot and immunolocalization, revealed that both are specifically expressed in the embryo but not in the endosperm and are dramatically downregulated by ABA.

Control of tuberisation in potato by gibberellins and phytochrome B

Abstract: Phytochrome B-deficient plants exhibit increased gibberellin (GA) levels or responsiveness, which may contribute to their elongated growth and reduced chlorophyll levels. We have investigated the effects of applications of gibberellic acid and an inhibitor of gibberellin biosynthesis, ancymidol, on wild-type and phytochrome B-antisense potato (Solanum tuberosum ssp. andigena) plants. The results showed that some phenotypes of the phytochrome B-antisense plants, i.e. increased stem length and reduced chlorophyll, can be mimicked by treating wild-type plants with gibberellic acid. However, another phenotype, i.e. tuberisation response in long days, is mimicked by application of a GA biosynthesis inhibitor ancymidol, thus appearing to be the result of a reduction in the gibberellin levels. A simple increase in gibberellin levels or sensitivity is, therefore, not sufficient to explain the phenotype of the antisense plants.

Priming-Induced Metabolic Changes in Sunflower (Helianthus annuus) Achenes Improve Germination and Seedling Growth

Abstract: Seed priming improves vigor, but priming agents may differ greatly in their effectiveness. The present study was performed to unravel the physiological basis of vigor improvement by priming sunflower achenes with pre-optimized levels of hydrogen peroxide (H2O2), salicylic acid (SA), thiourea (TU), gibberellic acid (GA3), ascorbic acid (AA), sodium chloride (NaCl), freezing and heating. Most of the treatments induced de novo synthesis of peptides with low (37 kDa for H2O2, SA and NaCl treatments, and 57 kDa for SA and TU treatments) and high (157 kDa for H2O2, SA, TU, GA3 and AA treatments and 167 kDa for SA treatment) molecular mass, reduced solute leakage, and an enhanced soluble sugar pool in the achenes. Priming reduced days to 50% germination (T50) and mean germination time (MGT) and improved germination energy (GE) and final germination percentage (FGP). Shoot length was improved by priming with H2O2, GA3, and NaCl; root length with NaCl and H2O2; shoot and root dry weight with H2O2, SA and AA. Positive correlations between GE and FGP and expressed peptides, soluble sugars, shoot and root length, and dry weight and negative ones with EC of leachate suggested that pre-germination changes in primed achenes, in addition to improve germination, show lasting effects in promoting seedling growth. Of the treatments, H2O2, SA, TU and GA3 were the most effective. Overall, the effects of priming treatments are related to de novo protein synthesis, an improved repair mechanism, and germination substrates for vigorous and earlier production of seedlings.

Somatic organogenesis and plant regeneration in Ricinus communis

Abstract: An in vitro propagation system was developed for castor-bean (Ricinus communis L. cv. TMV 6) through cotyledon derived callus cultures. The impact of different concentrations of auxins, cytokinins, additives, amino acids and sugars were evaluated for callus induction and shoot proliferation. Green compact nodular organogenic callus was obtained on the medium fortified with Murashige and Skoog (MS) salts, B5 vitamins, 2.0 mg dm−3 6-benzyladenine and 0.8 mg dm−3 α-naphthalene acetic acid (NAA). Multiple shoot proliferation from the callus cultures was achieved on the medium with MS salts, B5 vitamins, 2.5 mg dm−3 thidiazuron (TDZ), 0.4 mg dm−3 NAA and 15 mg dm−3 glutamine. During multiple shoot induction the phenolic secretion was controlled by the addition of 15 mg dm−3 polyvinylpyrolidone. The proliferated shoots were elongated on the medium comprising MS salts, B5 vitamins, 1.5 mg dm−3 TDZ and 0.3 mg dm−3 gibberellic acid. The elongated shoots were rooted on the medium containing MS salts, B5 vitamins, 0.3 mg dm−3 indole-3-butyric acid and 0.6 mg dm−3 silver nitrate. After root induction, the plants were hardened in earthen pots containing sand, soil and vermiculite.

Direct shoot regeneration from leaf explants of Spilanthes acmella

Abstract: Multiple shoots of Spilanthes acmella Murr. were induced from nodal buds of in vivo and in vitro seedlings on Murashige and Skoog (MS) medium containing 1.0 mg dm−3 6-benzyladenine (BA) and 0.1 mg dm−3 α-naphthalene-acetic acid (NAA). Adventitious shoots were successfully regenerated from the leaf explants derived from the above mentioned multiple shoots. The efficiency of shoot regeneration was tested in the MS medium containing BA, kinetin, or 2-isopentenyl adenine in combination with NAA, indole-3-acetic acid (IAA), or indole-3-butyric acid (IBA) and gibberellic acid. Maximum number of shoots per explant (20 ± 0.47) was recorded with 3.0 mg dm−3 BA and 1.0 mg dm−3 IAA. An anatomical study confirmed shoot regeneration via direct organogenesis. About 95 % of the in vitro shoots developed roots after transfer to half strength MS medium containing 1.0 mg dm−3 IBA. 95 % of the plantlets were successfully acclimatized and established in soil. The transplanted plantlets showed normal flowering without any morphological variation.

Effects of Some Plant Growth Regulators on Leaf Anatomy of Radish Seedlings Grown Under Saline Conditions

Abstract: In this work, the effects of gibberellic acid, ethylene, 24-epibrassinolide, triacontanol and polyamine (cadaverine, putrescine, spermidine, spermine) pretreatments on the leaf anatomy of radish seedlings grown under saline conditions were studied. Salt stress decreased the stomata number, epidermis cell number and width, leaf thickness and distance between vascular bundles in the varying degrees in the control seedlings non-pretreated with the growth regulators, in comparison with leaves of the ones in distilled water medium. On the other hand, it was observed that the growth regulator pretreatments affected in different degrees on the leaf anatomy of radish seedlings, and this difference was signifi cant.

Androgenic potential in coconut ( Cocos nucifera L.)

Abstract: Conditions for induction of androgenesis in coconut cv. Sri Lanka Tall were studied. Anthers collected from inflorescences at four maturity stages were given heat (38°C) or cold (4°C) pretreatments for 1, 3, 6 and 14 days, either prior to or post inoculation. Three different basal media and different anther densities were also tested. Androgenesis was observed only in anthers collected from inflorescences 3 weeks before splitting (WBS) and after a heat pretreatment at 38°C for 6 days. Modified Eeuwens Y3 liquid medium supplemented with 100 μM 2,4-dichlorophenoxyacetic acid (2,4-d), 0.1% activated charcoal and 9% sucrose was effective in inducing an androgenic response. The lowest anther density tested, 10 per petri plate, was found to be the optimal density. When androgenic calli or embryos were subcultured to Y3 medium containing 66 μM 2,4-d, followed by transfer to Y3 medium without plant growth regulators and finally to Y3 medium containing 5 μM 6-benzyladenine (BA) and 0.35 μM gibberellic acid (GA3), plantlets regenerated at a frequency of 7%. Histological study indicated that the calli and embryos originated from the inner tissues of the anthers. Ploidy analysis of calli and embryos showed that they were haploid. This is the first report of successful androgenesis yielding haploid plants from coconut anthers.

Gibberellic acid-mediated salt signaling in seed germination.

Abstract: Seed germination initiates the postembryonic development of plants, which determines successful seedling establishment and plant propagation. It is therefore tightly regulated by diverse environmental conditions, including high salinity and drought, as well as by intrinsic developmental programs, among which gibberellic acid (GA) is best understood. Regulatory roles of GA in seed germination have been extensively studied. It is also known that high salinity inhibits germination by repressing genes encoding GA biosynthetic enzymes. However, it is still unclear how salt signals are coordinately incorporated into the GA signaling pathway at the molecular level. We recently demonstrated that a membrane-bound NAC transcription factor, NTL8, mediates salt signaling, primarily through a RGL2-independent GA pathway, in regulating seed germination. High salinity promotes NTL8 transcription and proteolytic activation of NTL8. Notably, the NTL8-mediated salt signaling is independent of abscisic acid (ABA). These observations indicate that membrane-mediated transcription control is an important component of salt signaling during seed germination.

Seed germination of Solanum spp. (Solanaceae) for use in rehabilitation and commercial industries

Abstract: Effective methods for propagation of native Solanum species are required for mine rehabilitation and the native food industry in Australia. This study investigated seed germination of eight native Solanum species with respect to incubation temperature and the efficacy of germination-promoting compounds gibberellic acid (GA3), the butenolide isolated from smoke (karrikinolide, KAR1) and smoke water (SW). Seeds of all species were tested under a temperature regime of 26/13°C or 33/18°C. In these conditions, seeds of only two species, S. cunninghamii Benth. and S. phlomoides Benth. germinated to high levels without treatment. Of the remaining six species, GA3 alone promoted germination in S. chippendalei Symon, S. diversiflorum F.Muell. and S. sturtianum F.Muell., whereas GA3, KAR1 and SW were effective at promoting germination of S. centrale J.M.Black, S. dioicum W.Fitzg. and S. orbiculatum Dunal ex Poir. to varying degrees. Additional incubation temperatures (10, 15, 20, 25 and 30°C) were examined for S. centrale and S. orbiculatum. For both species, broadly similar patterns were noted in the response of seeds to GA3, KAR1 and SW across all temperatures. However, for S. centrale seeds, germination percentages were higher at 26/13°C than at any of the constant temperatures, and there was a trend of increasing germination with increasing constant temperature for S. orbiculatum seeds. Analysis of seed embryo type and imbibition characteristics and consideration of the subsequent germination results indicates that dormant Solanum seeds possess physiological dormancy.

Plant growth regulators treatments modulate growth, physiology and quality characteristics of cucumis melo l. plants

Abstract: Our objective was to identify the effects of Gibberellic acid (GA3), Prohexadione-Calcium (Prohex-Ca), Cycocel and Ethephon applied as foliar sprays, on pre- and post-harvest physiology and quality characteristics of melon (Cucumis melo L.). GA3 promoted melon growth, while a significant inhibition with Cycocel and Ethephon was observed. The chlorophyll a+b concentration as well as the chlorophyll fluorescence characteristics were negatively affected by Prohex-Ca, Cycocel and Ethephon application. The maximum quantum yield of PSII (Fv/Fm) was declined showing an impairment of the primary photochemical efficiency of the photosynthetic apparatus during the time course of the experiment. The significant decrease of Fv/Fo is an indicator of structural damage, which occur in the thylakoids and affects the photosynthetic electron transport. With GA3 application, fructose, glucose and soluble solids remained unchanged, whereas ascorbic acid content increased significantly. With the retardants a significant decrease in sugars, soluble solids and ascorbic acid content and an increase in respiration rate and in titratable acidity of fruits, was induced. Less soluble solids accumulation in melon from plants treated with growth retardants could be a consequence of delayed maturity, a fact that it can be proved by the lower maturity index.

Growth Regulators and Chemicals Stimulate Germination of Leafy Spurge (Euphorbia esula) Seeds

Abstract: Baseline information on inducing germination of dormant leafy spurge seeds with growth regulators and chemicals is lacking. This study was conducted to survey the effect of various substances on germination of leafy spurge seeds. The nontreated control seeds in this population were nearly fully imbibed in 3 h and displayed approximately 35% germination in 21 d under the normal alternating temperature of 20/30 C (16/8 h). Gibberellic acid (GA3, 10 mM) induced 65% germination at constant temperatures of 20 and 30 C. The alternating temperature increased the effectiveness of 10 mM GA3 with 94% germination, a twofold increase over the control. Nontreated seeds did not germinate at the constant temperatures, suggesting that alternating temperature acts via a GA-independent pathway. Kinetin at 0.1 to 1 mM was no more effective than the control, but a saturated solution of kinetin induced 73% germination. Ethephon at 0.01 to 1 mM induced 58 to 66% germination, although there was little response to different concentrations. Ethylene gas at 1 ppm stimulated germination to 77%, a 1.8-fold increase over the control. Germination of seeds incubated continuously in 1 and 10 mM nitrate displayed 35 and 40% germination, respectively. Seeds pulsed for 24 h with 100 mM nitrate displayed 58% germination after 21 d. Potassium phosphate– citrate buffer (pH 3.4) and its individual components induced 60 to 70% germination. Fluridone (10 and 100 mM), 1-naphthaleneacetic acid (NAA, 0.1 to 10 mM), and ethanol (0.2 to 15%) had no effect on germination, but subsequent elongation in the presence of NAA was inhibited because of swelling of the radicle. This research reveals that GA3 is the most effective growth regulator for germination of dormant leafy spurge seeds, and its effect is independent of temperature. Nomenclature: Leafy spurge, Euphorbia esula L. EPHES.

Changes in activities of antioxidant enzymes during Chenopodium murale seed germination

Abstract: The activities and isoenzyme pattern of catalase (CAT), superoxide dismutase (SOD) and peroxidase (POD) have been studied during germination of Chenopodium murale seeds CAT and SOD activities were similar in dry seeds and during first 2 d of imbibition CAT activity increased during radicle protrusion and early seedling development The maximum SOD activity was found at final stages of germination and early seedling development POD activity was not detected until the 6th day of germination, indicating POD involvement not until early seedling development Gibberellic acid (GA3, 160 µM) delayed and synchronized C murale germination

Methods to break seed dormancy of Astragalus cyclophyllon

Abstract: The aim of this study was to enhance the germination rate of Astragalus cyclophyllon seeds which have a very low germination rate under normal conditions. The seeds were soaked for 72 h in 100, 200, 300, 400 and 500 ppm gibberellic acid (GA3) solution, H2SO4 concentrations (50 and 98%) at two treatment times (5 and 10 min) and 60, 80 and 100oC hot water at two treatment times (5 and 10 min) before placing in Petri dishes. The fresh seeds (non-stratified) of A. cyclophyllon had 55% germination. Analysis of variance indicated that both GA3 and H2SO4 concentrations had significant effects on seed germination and final germination percentage. The highest germination percentage (81%) was obtained when the seeds were treated with 500 ppm GA3. The results showed that hot water treatments are not useful methods for breaking the seeds dormancy.

A GAMYB-like gene in tomato and its expression during seed germination

Abstract: To understand the function of the gibberellin (GA) transduction pathway during germination, the transcription factor gene GAMYB, which responds to the GA signal, has been studied in tomato (Solanum lycopersicum) seeds. This gene, called LeGAMYBL1 is present as a single copy, and is expressed in both the embryo and endosperm during seed germination in gib-1 mutant (non-GA producing) and wild-type (cv. Glamour) seeds. It is also expressed in young vegetative tissues. There is an 83% similarity in the amino acid sequence of the binding domain of the protein that is encoded by this tomato GAMYB-like gene when compared to that encoded by the GAMYB genes from barley, rice and Arabidopsis. In both mutant and wild-type intact tomato seeds, LeGAMYBL1 expression increases during germination, is upregulated by gibberellic acid (GA3), and declines thereafter. LeGAMYBL1 transcripts are also present in non-germinating gib-1 mutant seeds imbibed in water, and they are upregulated by GA3 during promotion of germination. However, dissected gib-1 embryos complete germination when imbibed in either water or GA3, with almost no difference in the amount of mRNA transcribed by the LeGAMYBL1 gene during this event. This is indicative that GA3 is not required for the expression of the LeGAMYBL1 gene, which is likely necessary, but not sufficient, for germination to be completed, especially in the intact seed. The germination-inhibiting hormone abscisic acid does not influence expression of this gene. Expression of the LeGAMYB1 gene also occurs in the endosperm, but there is no correlation between its expression and GA-promoted expression of the cell-wall-degrading enzyme endo-β-mannanase.

Reduced temperature, elevated sucrose, continuous light and gibberellic acid promote corm formation in Watsonia vanderspuyiae

Abstract: Storage organ induction in vitro can limit the loss of plants during acclimatisation, and can substantially reduce the time to flower following acclimatisation. An initial experiment lasting 3 months showed that of the four Watsonia species investigated, only Watsonia vanderspuyiae was capable of consistent corm formation. Consequently, a second study investigating light, temperature (10, 15, 20 and 25°C), carbohydrates (sucrose at 3, 6, 9 or 12%) and plant growth regulators [α-naphthalene acetic acid (NAA), N 6-benzylaminopurine (BA), abscisic acid (ABA), gibberellic acid 3 (GA3), paclobutrazol (PAC) and methyl jasmonate (MeJa)], lasting 6 months, was performed. Abnormal corms were produced by W. lepida in response to ABA, but normal corms formed at lower temperatures (10 and 20°C). In contrast, corms were produced in most treatments of W. vanderspuyiae, with BA, PAC and ABA being the only treatments that inhibited corm induction. By examining the product of the proportion corm induction multiplied by corm mass, four treatments superior to the control (20°C, 1 mg l−1 GA3, 6% sucrose and continuous light) were selected for a factorial design experiment in W. vanderspuyiae. After 3 months, treatments were ranked according to their product. The best four combinations of these four factors all contained GA3 and were incubated at 20°C, suggesting synergistic interactions between gibberellins and reduced temperature.

Cyclic somatic embryogenesis and efficient plant regeneration from callus of safflower

Abstract: Efficient plant regeneration through somatic embryogenesis was established for safflower (Carthamus tinctorius L.) cv. NARI-6. Embryogenic calli were induced from 10 to 17-d-old cotyledon and leaf explants from in vitro seedlings. High frequency (94.3 %) embryogenic callus was obtained from cotyledon explants cultured on Murashige and Skoog’s germination (MSG) basal medium supplemented with thidiazuron, 2-isopentenyladenine and indole-3-butyric acid. Primary, secondary and cyclic somatic embryos were formed from embryogenic calli in a different media free of plant growth regulators, however, 100 % cyclic somatic embryogenesis was obtained from cotyledon derived embryogenic calli cultured on MSG. Somatic embryos matured and germinated in quarter-strength MSG medium supplemented with gibberellic acid. Cotyledons with root poles or non root poles were converted to normal plantlets and produced adventitious roots in rooting medium. Rooted plants were acclimatized and successfully transferred to the field.

The effect of in vivo and in vitro applications of ethrel and GA3 on sex expression in bitter melon (Momordica charantia L.)

Abstract: Bitter melon (Momordica Charantia L.) is an important vegetable crop with nutritional and medicinal qualities. As a member of cucurbitaceae it is monoecious with varying proportions of staminate and pistillate flowers. This study was undertaken to determine the effects of various applications of ethrel and gibberellic acid (GA3) on sex modification in M. charantia. In the first set of experiments, various concentrations of hormones were added to the seed germination medium, in the second, adult plants growing in the field were sprayed with aqueous solutions of ethrel or GA3 three times at three-day intervals. The number and sex of open flowers was recorded daily for 60 days after the first flower opened and total number of staminate and pistillate flowers was calculated at the end of the experiment. The highest frequency (29.5%) of pistillate flowers was observed in plants treated with 500 ppm ethrel at germination. Similarly, spraying of adult plants with 100 ppm GA3 increased the proportion of pistillate flowers to 26% relative to 15% in untreated controls. Both ethrel and GA3 induced significantly higher number of pistillate flowers than control. In vitro hormone application during seed germination was much more successful than spraying of field grown plants.