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PubMed1992

Regulation of Gibberellin Biosynthesis in Gibberella fujikuroi.

Gibberellin production by Gibberella fujikuroi started only after the nitrogen source was depleted and ceased upon its renewal. Nitrogen repression of gibberellin biosynthesis is not an indirect effect of the growth arrest that follows the depletion of an essential nutrient because gibberellins were not produced upon depletion of phosphate. Mycelia produced gibberellins when suspended in a glucose solution. Production ceased some time after depletion of glucose and resumed upon its readdition. Under certain conditions, the gibberellin production rate was inversely proportional to the glucose concentrations. The specific regulation of gibberellin biosynthesis by the nitrogen source imposes a revision of the concept that gibberellins are secondary metabolites whose production is triggered by imbalance or cessation of growth.

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PubMed1969

Similarities between gibberellins and related compounds in inducing Acid phosphatase and reducing sugar release from barley endosperm.

Barley endosperm halves release acid phosphatase in response to several gibberellins and gibberellin precursors. Seed halves incubated with 10(-7)m GA(3) at 29 degrees begin to release phosphatase after 11 hr and release it for another 26 hr in response to GA(3). After 37 hr, the rate of release slows to that of seed halves incubated without GA(3). GA(3) is active at 10(-10)m and maximally active at 10(-7)m. Comparative activity of 12 gibberellins and gibberellin precursors is GA(1) = GA(3) > GA(2) > GA(4) = GA(7) > GA(5) = GA(13) > GA(14) > GA(8) = GA(9) > (-)kaurenoic acid > (-)-kaurene. These compounds show the same order of activity and approximately the same relative activity in inducing reducing sugar release as in inducing phosphatase activity. The activity of each compound increases with its presumed position in a biosynthetic pathway leading from kaurene to GA(3). This correlation suggests that activity may be a reflection of the efficiency of conversion to an active form within the seed half.The ease of measuring the acid phosphatase response and the sensitivity of the seed halves to low concentrations of many gibberellins and gibberellin precursors makes this a useful bioassay for gibberellin-like substances.

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PubMed1969

Auxins and Gibberellin-like Substances in Parthenocarpic and Non-parthenocarpic Syconia of Ficus carica L., cv. King.

In the King cultivar of fig, the first crop is parthenocarpic, develops on previous year's growth, and a series of supernumerary ovules develops within the original ovules. The second crop, formed on current-season's growth, requires fertilization. To determine whether the 2 crops differed in types, and in patterns of concentrations of total ;free' auxins and acidic gibberellins, they were extracted from weekly fruit samples. Timing of the 3 peaks of total auxins and the single peak of gibberellins was identical in the 2 crops. The first auxin peak in both occurred at the end of fruit growth period I (first rapid growth period), the second shortly before the end of period II (period of slow growth), and the rise and fall in concentrations of the third peak accompanied the rise and fall of the fruit growth rate in period III. The end of period II was marked by the single gibberellin peak. Additional peaks before the first sampling dates, of auxins in the first crop, of gibberellins in the second, were indicated by high concentrations in the first samples and subsequent rapid decline. The same 4 individual auxins appeared in both crops. Auxins I and II were highest in concentration in the first total auxin peak of both crops. In the second peak of the first crop, auxins II and III were highest, whereas in that peak of the second crop auxins II and IV were highest. Qualitative differences in gibberellins occurred in the 2 crops. In general, auxin concentrations were higher in the first than the second crop, and gibberellin concentrations higher in the second. High concentrations of gibberellins coincided with low ones of auxins, and vice versa.

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PubMed1972

Tannins as gibberellin antagonists.

Fourteen chemically defined hydrolyzable tannins and six impure mixtures of either condensed or hydrolyzable tannins were found to inhibit the gibberellin-induced growth of light-grown dwarf pea seedlings. The highest ratio of tannins to gibberellic acid tested (1000: 1 by weight) inhibited from 80 to 95% of the induced growth for all tannins tested except for two monogalloyl glucose tannins which inhibited only 50% of the induced growth. The lowest ratio tested (10: 1) inhibited the induced growth by less than 25% except for the case of terchebin where 50% inhibition was found. The inhibition of gibberellin-induced growth was found to be completely reversed by increasing the amount of gibberellin in three cases tested. Tannins alone did not inhibit endogenous growth of either dwarf or nondwarf pea seedlings. Eight compounds related to tannins, including coumarin, trans-cinnamic acid, and a number of phenolic compounds were also tested as gibberellin antagonists. Most of these compounds showed some inhibition of gibberellin-induced growth, but less than that of the tannins. At the highest ratio (1000: 1) the greatest inhibition was 55%; at the lowest ratio (10: 1) no more than 17% was observed. These compounds did not inhibit endogenous growth, and the inhibition of gibberellin-induced growth could be reversed by increasing the amount of gibberellin in two cases tested.Six chemically defined tannins were found to inhibit hypocotyl growth induced by gibberellic acid in cucumber seedlings. Growth induced by indoleacetic acid in the same test was not inhibited. The highest ratio of tannin to promotor tested gave strong inhibition of gibberellic acid-induced growth, but actually enhanced the growth induced by indoleacetic acid. This difference in action suggests a specificity between the tannins and gibberellic acid.

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PubMed1982

Comparative Effects of Substituted Pyrimidines on Growth and Gibberellin Biosynthesis in Gibberella fujikuroi.

The fungicide alpha-(2,4-dichlorophenyl)-alpha-phenyl-5-pyrimidine methyl alcohol (triarimol) and four other structural analogs of this substance, in which one or more of the substituents were varied, were tested for their comparative effects on growth and gibberellin biosynthesis in the fungus Gibberella fujikuroi. Each of the five analogs tested was capable of inhibiting growth as measured by dry weight in 5-day-old cultures. Three of them [alpha-(2-chlorophenyl)-alpha-(4-chlorophenyl)-5-pyrimidine methyl alcohol, fenarimol; alpha-(2-chlorophenyl)-alpha-(4-fluorophenyl)-5-pyrimidine methyl alcohol, nuarimol; and triarimol] were effective at appreciably lower concentrations than the other two [alpha-(4-chlorophenyl)-alpha-(1-methylethyl)-5-pyrimidine methyl alcohol, experimental compound EL 509; and alpha-cyclopropyl-alpha-(4-methoxyphenyl)-5-pyrimidine methyl alcohol, ancymidol].All five substances also inhibited gibberellin production as measured by gibberellin content of fungus filtrates. The relative effectiveness of the compounds as inhibitors of growth and gibberellin production were similar. These analogs were also shown to inhibit ent-kaurene oxidation by microsomal preparations from fungal mycelia. Thus, the site of inhibition of gibberellin biosynthesis may be the same for the fungus as the one affected by this group of substances in higher plant tissues.The structure-activity relationships between the analogs are opposite to those observed in higher plant tissues. The fungicides fenarimol, nuarimol, and triarimol, which were most effective in inhibiting growth and gibberellin biosynthesis in the fungus, were much less effective than EL 509 and ancymidol in inhibiting growth and gibberellin biosynthesis in higher plants. These results indicate that the ent-kaurene oxidase systems from the two sources have somewhat different molecular characteristics, and thus, interact differently with this group of substances.

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PubMed1987

Gibberellin-Induced Changes in the Populations of Translatable mRNAs and Accumulated Polypeptides in Dwarfs of Maize and Pea.

Two-dimensional gel electrophoresis was used to characterize the molecular mechanism of gibberellin-induced stem elongation in maize and pea. Dwarf mutants of maize (d-5) and pea (Progress No. 9) lack endogenous gibberellin (GA(1)) but become phenotypically normal with exogenous applications of this hormone. Sections from either etiolated maize or green pea seedlings were incubated in the presence of [(35)S] methionine for 3 hours with or without gibberellin. Labeled proteins from soluble and particulate fractions were analyzed by two-dimensional gel electrophoresis and specific changes in the patterns of protein synthesis were observed upon treatment with gibberellin. Polyadenylated mRNAs from etiolated or green maize shoots and green pea epicotyls treated or not with gibberellin (a 0.5 to 16 hour time course) were assayed by translation in a rabbit reticulocyte extract and separation of products by two-dimensional gel electrophoresis. Both increases and decreases in the levels of specific polypeptides were seen for pea and corn, and these changes were observed within 30 minutes of treatment with gibberellin. Together, these data indicate that gibberellin induces changes in the expression of a subset of gene products within elongating dwarfs. This may be due to changes in transcription rate, mRNA stability, or increased efficiency of translation of certain mRNAs.

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PubMed1990

Comparison of gibberellins in normal and slender barley seedlings.

Gibberellins A(1), A(3), A(8), A(19), A(20), and A(29) were identified by full scan gas chromatography-mass spectrometry in leaf sheath segments of 7-day-old barley (Hordeum vulgare L. cv Golden Promise) seedlings grown at 20 degrees C under long days. In a segregating population of barley, cv Herta (Cb 3014), containing the recessive slender allele, (sln 1) the concentration of GA(1) and GA(3) was reduced by 10-fold and 6-fold, respectively, in rapidly growing homozygous slender, compared with normal, leaf sheath segments. However, the concentration of the C(20) precursor, GA(19), was nearly 2-fold greater in slender than in normal seedlings. There was little difference in the ABA content of sheath segments between the two genotypes. The gibberellin biosynthesis inhibitor, paclobutrazol, reduced the final sheath length of normal segregants (50% inhibition at 15 micromolar) but had no effect on the growth of slender seedlings at concentrations below 100 micromolar. There was a 15-fold and 4-fold reduction in GA(1) and GA(3), respectively, in sheath segments of 8-day-old normal seedlings following application of 10 micromolar paclobutrazol. The same treatment also reduced the already low concentrations of these gibberellins in slender segregants. The results show that the pool sizes of gibberellins A(1) and A(3) are small in slender barley and that leaf sheath extension in this genotype appears to be gibberellin-independent. The relationship between gibberellin status and tissue growth-rate in slender barley is contrasted with other gibberellin nonresponsive, but dwarf, mutants of wheat (Triticum aestivum) and maize (Zea mays).

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PubMed1990

Genetic analysis of the role of gibberellin in the red light inhibition of stem elongation in etiolated seedlings.

Red light causes a reduction in the extension growth of dark-grown seedlings. The involvement of gibberellin in this process was tested by screening a number of gibberellin synthesis and gibberellin response mutants of Pisum sativum L. for the kinetic response of stem growth inhibition by red light. Gibberellin deficient dwarfs, produced by mutant alleles at the Le, Na, and Ls loci, and gibberellin response mutants produced by mutant alleles at the La and Cry(2), Lka, and Lkb loci were tested. Extension growth of expanding third internodes of dark-grown seedlings was recorded with high resolution using angular position transducers. Seedlings were treated with red light at a fluence rate of 4 micromoles per square meter per second either continuously or for 75 seconds, and the response was measured over 9 hours. With certain small exceptions, the response to the red light treatments was similar in all the mutants and wild types examined. The lag time for the response was approximately 1 hour and a minimum in growth rate was reached by 3 to 4 hours after the onset of the light treatment. Growth rate depression at this point was about 80%. Seedlings treated with 75 seconds red light recovered growth to a certain extent. Red/far-red treatments indicated that the response was mediated largely by phytochrome. The similar responses to red light among these wild-type and mutant genotypes suggest that the short-term (i.e. 9 hour) response to red light is not mediated by either a reduction in the level of gibberellin or a reduction in the level or affinity of a gibberellin receptor.

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PubMed1992

Regulation of gibberellin formation by the fungus Gibberella fujikuroi.

Gibberellins are a classic example of the production of plant growth regulators by microorganisms. They are important biotechnological products and are increasingly used in agriculture and horticulture. The economic importance of these plant hormones has led to an extensive study of the regulation of gibberellin biosynthesis. There have been reports of light, growth rate, inoculum size and carbon and ammonium sources acting as regulators of gibberellic acid biosynthesis. Besides light stimulation, nitrogen repression is a well-known regulatory principle of secondary metabolite formation. In Gibberella fujikuroi ammonium interferes with the production of gibberellic acid whereas phosphate does not influence the biosynthesis. It was found that the negative effect of ammonium ions is due to both the inhibition of activity and the repression of de novo synthesis of specific gibberellin-producing enzymes. Besides nitrogen control, the biosynthesis of gibberellins is suppressed by glucose. This glucose effect can be overcome by the addition of mevalonic acid. Therefore, the key enzyme of the isoprenoid pathway, the HMG-CoA reductase, seems to be the target of C-catabolite repression. A detailed knowledge of the regulation of gibberellin biosynthesis is important for fermentation processes. The biological function of gibberellin formation for the producing fungus is discussed.

Carbon↗

PubMed1998

Gibberellin biosynthetic pathway in Gibberella fujikuroi: evidence for a gene cluster.

Differential screening of a Gibberella fujikuroi cDNA library was used to successfully clone and identify genes involved in the pathway of gibberellin biosynthesis. Several cDNA clones that hybridized preferentially to a cDNA probe prepared from mycelium induced for gibberellin production were isolated and characterized. The deduced amino acid sequences of two (identical) clones contained the conserved heme-binding motif of cytochrome P450 monooxygenases (FXXGXXXCXG). One of these cDNA fragments was used as a homologous probe for the screening of a genomic library. A hybridizing 6.7-kb genomic SalI fragment was cloned into pUC19. The sequencing of this clone revealed that a second cytochrome P450 monooxygenase gene was closely linked to the first one. Since at least four cytochrome P450 monooxygenase-catalyzed steps are involved in the synthesis of gibberellins, chromosome walking was performed to find a further gene of this family or other genes involved in gibberellin pathway. Next to the two P450 monooxygenase genes, a putative geranylgeranyl diphosphate synthase gene, the copalyl diphosphate synthase gene, which is the first specific gene of the gibberellin pathway, and a third P450 monooxygenase gene were identified. These results suggest that at least some of the genes involved in the biosynthesis of gibberellins are closely linked in a gene cluster in G. fujikuroi, as has been recently found for other "dispensable" pathways in fungi.

Alkyl and Aryl Transferases↗

PubMed1998

Gibberellin biosynthesis in Gibberella fujikuroi: cloning and characterization of the copalyl diphosphate synthase gene.

The gene coding for copalyl diphosphate synthase (CPS), which represents the first gene of the gibberellin pathway, was isolated from the rice pathogen Gibberella fujikuroi. This fungus is used commercially for the production of gibberellic acid and related gibberellins. CPS is a terpene cyclase which catalyzes the first specific step of the gibberellin (GA) pathway as it branches off from the general isoprenoid (biosynthetic) pathway at geranylgeranyl disphosphate (GGDP). A cDNA fragment of the cps gene from the fungus G. fujikuroi was amplified by RT-PCR using oligonucleotides based on amino-acid sequences which were conserved between the plant CPSs and the bifunctional CPS/KS of the fungus Phaeosphaeria sp. L487. A 588-bp fragment obtained with nested PCR was used to isolate the corresponding genomic clone of the cps gene from the wild-type lambda-library. This gene consists of three exons and two introns. The three exons are 2877 bp long and encode 959 amino-acid residues. The protein shares 48% identity with the bifunctional Phaeosphaeria sp. L487 FCPS and between 16% and 18% identity to the corresponding plant CPSs. Expression of the G. fujikuroi cps gene is strongly enhanced under conditions optimized for gibberellin biosynthesis and is reduced when high amounts of ammonium are present in the medium. Gene disruption, followed by gibberellin assays and Southern-blot analysis of the transformants, demonstrated clearly that the cloned gene has the expected function in the biosynthesis of fungal gibberellins.

Alkyl and Aryl Transferases↗

PubMed2000

Gibberellin and abscisic acid signalling in aleurone.

The plant hormones gibberellin and abscisic acid regulate gene expression, secretion and cell death in aleurone. The emerging picture is of gibberellin perception at the plasma membrane whereas abscisic acid acts at both the plasma membrane and in the cytoplasm - although gibberellin and abscisic acid receptors have yet to be identified. A range of downstream-signalling components and events has been implicated in gibberellin and abscisic acid signalling in aleurone. These include the Galpha subunit of a heterotrimeric G protein, a transient elevation in cGMP, Ca2+-dependent and Ca2+-independent events in the cytoplasm, reversible protein phosphory-lation, and several promoter cis-elements and transcription factors, including GAMYB. In parallel, molecular genetic studies on mutants of Arabidopsis that show defects in responses to these hormones have identified components of gibberellin and abscisic acid signalling. These two approaches are yielding results that raise the possibility that specific gibberellin and abscisic acid signalling components perform similar functions in aleurone and other tissues.

Abscisic Acid↗

PubMed1999

'Green revolution' genes encode mutant gibberellin response modulators.

World wheat grain yields increased substantially in the 1960s and 1970s because farmers rapidly adopted the new varieties and cultivation methods of the so-called 'green revolution'. The new varieties are shorter, increase grain yield at the expense of straw biomass, and are more resistant to damage by wind and rain. These wheats are short because they respond abnormally to the plant growth hormone gibberellin. This reduced response to gibberellin is conferred by mutant dwarfing alleles at one of two Reduced height-1 (Rht-B1 and Rht-D1) loci. Here we show that Rht-B1/Rht-D1 and maize dwarf-8 (d8) are orthologues of the Arabidopsis Gibberellin Insensitive (GAI) gene. These genes encode proteins that resemble nuclear transcription factors and contain an SH2-like domain, indicating that phosphotyrosine may participate in gibberellin signalling. Six different orthologous dwarfing mutant alleles encode proteins that are altered in a conserved amino-terminal gibberellin signalling domain. Transgenic rice plants containing a mutant GAI allele give reduced responses to gibberellin and are dwarfed, indicating that mutant GAI orthologues could be used to increase yield in a wide range of crop species.

Alleles↗

PubMed1988

Interaction of a gibberellin-induced factor with the upstream region of an alpha-amylase gene in rice aleurone tissue.

The interaction between the DNA sequences of an alpha-amylase (EC 3.2.1.1) gene and a tissue-specific factor induced in rice (Oryza sativa L.) aleurone tissue by gibberellin was studied. DNA mobility-shift during electrophoresis indicated that a 500-base-pair sequence (HS500) of a rice alpha-amylase genomic clone (OSamy-a) specifically interacted with a factor from gibberellin-induced rice aleurone tissue. The amount of complex formed between the HS500 DNA fragment and the gibberellin-induced factor increased in proportion to increasing amounts of aleurone extract and decreased with the addition of unlabeled HS500 DNA fragment. A specific segment of the HS500 fragment was protected from exonuclease III digestion by protein(s) in the aleurone extract, revealing the approximate position of the protein-DNA interaction. In the protected region, there is a direct repeat that overlaps with a potential stem-loop structure. Protein in extracts from leaves, roots, or deembryonated seeds incubated without gibberellin A3 did not bind to the HS500 DNA fragment. However, the binding factor was induced in deembryonated seeds when exogenous gibberellin A3 was added during seed imbibition. This suggests that activation of alpha-amylase synthesis by gibberellin may be mediated by the formation of a factor that interacts with a specific sequence of the alpha-amylase gene.

Base Sequence↗

PubMed1995

Gibberellin biosynthesis in gib mutants of Gibberella fujikuroi.

The Ascomycete Gibberella fujikuroi synthesizes gibberellins, fujenal, carotenoids, and other terpenoids. Twelve gib mutants, isolated through the modified gibberellin fluorescence of their culture media, were subjected to chemical and biochemical analyses. Two mutants were specifically defective in the hydroxylation of carbon 13; their total gibberellin production was normal, but their main gibberellin was GA7 instead of GA3. Four mutants were blocked in the early reactions between geranylgeranyl pyrophosphate and 7-hydroxy-kaurenoic acid; two of them could not synthesize kaurene and another one was blocked in several oxidative steps. Six mutants had partial defects in early reactions, leading to the production of one-fifth to one-third of the wild type amounts of gibberellins and fujenal. Two of these produced considerable amounts of kaurenolides due to a defect in the conversion of kaurenoic acid to 7-hydroxykaurenoic acid. Another one produced no carotenoids, but attempts to isolate mutants of reactions shared by the carotenoid and gibberellin pathways failed. The gib mutations did not modify the ability of the fungus to live as a saprophyte.

Gibberella↗

PubMed2004

Expression of gibberellin 3 beta-hydroxylase gene in a gravi-response mutant, weeping Japanese flowering cherry.

Expressions of the gibberellin biosynthesis gene were investigated in a normal upright type and a gravi-response mutant, a weeping type of Japanese flowering cherry (Prunus spachiana), that is unable to support its own weight and elongates downward. A segment of the gibberellin 3 beta-hydroxylase cDNA of Prunus spachiana (Ps3ox), which is responsible for active gibberellin synthesis, was amplified by using real-time RT-PCR. The content of Ps3ox mRNA in the weeping type was much greater than that in the upright type, while the endogenous gibberellin level was much higher in the elongating zone of the weeping type. These results suggest that the amount and distribution of synthesized gibberellin regulate secondary xylem formation, and the unbalanced distribution of gibberellin affects the gravi-response of the Prunus tree.

Base Sequence↗

PubMed1984

Gibberellins and gene control in cereal aleurone cells.

The production of hydrolytic enzymes in the germinating cereal grain is considered as a model for plant cell differentiation. Recent literature is reviewed which suggests that gibberellins are involved in this process, but in a less straightforward manner than considered previously. It seems likely that only a subfraction of gibberellin is active and that production of this gibberellin is actually in the hydrolase-producing cells. These include aleurone cells and also the scutellar epithelial cells. At the intracellular level the action of gibberellin results in the accumulation of alpha-amylase mRNA and also mRNA for other unidentified proteins, referred to as gibb-ons. The alpha-amylase mRNAs are transcribed from two distinct gene families. The pattern of expression of alpha-amylase and gibb-on mRNAs is consistent with a common gibberellin-stimulated mechanism of control of for all of these genes. However it seems likely from experiments with ABA and from observations on gibb-on gene expression in non-aleurone cells that gibberellin does not have a role determining the specificity of gene expression, but rather acts as a general stimulator of mRNA accumulation.

Electrophoresis, Agar Gel↗

PubMed1966

Variations in Endogenous Gibberellins in Developing Bean Seeds II. Changes Induced in Acidic and Neutral Fractions by GA(1).

Immature (8-mm), medium mature (11-mm), and mature green (16- and 17-mm) bean seeds (Phaseolus vulgaris L. cv. Kentucky Wonder and Bountiful) were incubated in gibberellin A(1) solutions for 24 hours at 20 degrees . Extracts from the seeds were separated into nonacidic, acidic ethyl acetate, and acidic butanol fractions. These were chromatographed. The eluates of the chromatograms were tested on Progress No. 9 dwarf peas grown under red light. The level of neutral gibberellin-like substances remained unchanged in immature seed, but they increased markedly in mature green seeds. Coincident with increased levels of the neutral substances, there were significant decreases in acidic ethyl acetate-soluble gibberellin-like substances, including applied GA(1), and in 1 acidic butanol-soluble gibberellin-like substance. Seed incubation in GA(1) brought about increased activity of substance B-II in immature and medium mature seeds. The level of butanol-soluble gibberellin-like substance B-I in seeds of any size was not affected by incubation in GA(1). Considering the marked increases in activity induced in the neutral fraction and the decreases in activity of certain eluates from the chromatograms of the acidic fractions, it was concluded that the neutral fraction may serve as a reserve form of gibberellins in the dry seed. The acidic ethyl acetate substances and substance B-II may be required for normal development of the bean seed.

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