Gibberellins: a phytohormonal basis for heterosis in maize.

Four commercially important maize parental inbreds and their 12 F(1) hybrids were studied to investigate the role of the phytohormone gibberellin (GA) in the regulation of heterosis (hybrid vigor). All hybrids grew faster than any inbred. In contrast, all inbreds showed a greater promotion of shoot growth after the exogenous application of GA(3). Concentrations of endogenous GA(1), the biological effector for shoot growth in maize, and GA(19), a precursor of GA(1), were measured in apical meristematic shoot cylinders for three of the inbreds and their hybrids by gas chromatography-mass spectrometry with selected ion monitoring; deuterated GAs were used as quantitative internal standards. In 34 of 36 comparisons, hybrids contained higher concentrations of endogenous GAs than their parental inbreds. Preferential growth acceleration of the inbreds by exogenous GA(3) indicates that a deficiency of endogenous GA limits the growth of the inbreds and is thus a cause of inbreeding depression. Conversely, the increased endogenous concentration of GA in the hybrids could provide a phytohormonal basis for heterosis for shoot growth.

Identification of Antheridiogens in Lygodium circinnatum and Lygodium flexuosum.

Antheridiogens in two species of Schizaeaceous ferns, Lygodium circinnatum and Lygodium flexuosum, were analyzed by gas chromatography-mass spectrometry. In L. circinnatum, gibberellin A73 (GA73) methyl ester (GA73-Me), which had originally been identified in L. japonicum, was identified as a principal antheridiogen, and the methyl esters of five known GAs (GA9, GA20, GA70, GA88, and 3-epi-GA88) were also identified as minor antheridiogens. In addition, four compounds corresponding to isomers of monohydroxy-GA73-Me were detected. One of these was shown to be 12[beta]-hydroxy-GA73-Me, the parent acid of which has been allocated the GA assignment GA96. The other three compounds, tentatively named X1, X2, and X3, have not been fully characterized. In L. flexuosum, GA73-Me was also identified as a major antheridiogen, with X2 being detected as a minor one. The total antheridium-formation activity in the culture medium of 7-week-old prothallia of L. circinnatum and L. flexuosum was more than 1000 times higher than that of L. japonicum. On the other hand, the response of gametophytes of the former two Lygodium ferns to GA73-Me was more than 100 times lower than that of L. japonicum.

Biosynthesis of GA73 Methyl Ester in Lygodium Ferns.

Biosynthesis of GA73 methyl ester (GA73-Me), the principal antheridiogen in Lygodium ferns, was investigated. From the methanol extract of prothallia of Lygodium circinnatum, GA25, GA73, GA73-Me, GA88-Me, and a few unknown GA73 derivatives were detected by GC-MS. Because the presence of GA25 suggests that GA24, a direct precursor of GA25, could also be present in L. circinnatum prothallia, we used feeding experiments to investigate the possibility that GA24 is a precursor of GA73-Me. In L. circinnatum prothallia, [2H2]GA24 was converted into [2H2]GA73-Me and a trace amount of [2H2]GA9-Me, whereas [2H3]GA9 was converted into [2H3]GA9-Me and [2H3]monohydroxy-GA9-Me. Because GA73-Me, GA9-Me, and their monohydroxy derivatives had been identified by GC-MS from the culture medium of L. circinnatum prothallia, our results suggest that GA73-Me is biosynthesized from GA24 via GA73, and that neither GA9 nor GA9-Me is a precursor of GA73-Me. Though the possibility had been suggested that GA73-Me is biosynthesized from 9,15-cyclo-GA9 (GA103), [2H2]GA103 was not converted into [2H2]GA73-Me.

Gibberellins in seedlings and flowering trees of Prunus avium L.

Extracts of acids from mature seeds, germinating seeds, first, second and third year seedlings as well as mature, flowering trees of sweet cherry (Prunus avium L. cv. Stella) were analysed by gas chromatography-mass spectrometry. The presence of the known gibberellins (GAs) GA1 (1), GA3 (4), GA5 (7), GA8 (11), GA19 (14), GA20 (12), GA29 (13), GA32 (5), GA85 (2), GA86 (3) and GA87 (6) was confirmed by comparison of their mass spectra and Kovats retention indices with those of standards or literature values. In addition, 16alpha,17-dihydrodihydroxy GA25 (16) was identified and its stereochemistry confirmed by rational synthesis. The 12alpha,13-dihydroxy GAs, GA32 (5), GA86 (2), GA86 (3) and GA87 (6), were detected in mature seeds, germinating seeds and young seedlings, but not in flowering plants. The 13-hydroxy GAs, GA1 (1) and GA3 (4), were present in germinating seeds and, in addition to these, GA5 (7), GA8 (11), GA19 (14), GA20 (12) and GA29 (13) were detected in seedlings and mature flowering plants. In germinating seeds and seedlings (while the plants were growing actively), concentrations of the 12alpha,13-dihydroxy GAs, measured by bioassay, declined and those of the 13-hydroxy GAs increased. The results are discussed with reference to the known and predicted effects of the GAs on the vegetative growth and flowering of P. avium plants.

Identification of endogenous gibberellins in strawberry, including the novel gibberellins GA123, GA124 and GA125.

Extracts of carboxylic acids from immature fruits of strawberry (Fragaria x ananassa Duch. cv. Elsanta) were analysed for gibberellins by combined gas chromatography-mass spectrometry. The following previously characterised gibberellins were identified by comparison of their mass spectra and Kovats retention indices (KRIs) with those of standards or published data: GA1, GA3, GA5, GA8, GA12, GA17, GA19, GA20, GA29, GA44, GA48, GA49, GA53, GA77, GA97, GA111 and GA112. Evidence for endogenous 1-epi GA61 (GA119) and 11alpha-OH-GA12 was also obtained. In addition, a number of putative GAs were detected. Of these, three were shown to be 12alpha-hydroxy-GA53, 12alpha-hydroxy-GA44, and 12alpha-hydroxy-GA19 by comparison with authentic compounds prepared by rational synthesis, and have been allocated the descriptors GA123, GA124 and GA125, respectively.

Endogenous gibberellins in immature seeds of Prunus persica L.: identification of GA(118), GA(119), GA(120), GA(121), GA(122) and GA(126).

The endogenous gibberellins in immature seeds of Prunus persica were analyzed by gas chromatography-mass spectrometry. Eleven known gibberellins, GA(3), GA(9), GA(17), GA(19), GA(30), GA(44), GA(61), GA(63), GA(87), GA(95) and GA(97) were identified. Additionally, several hitherto unknown gibberellins were detected and their putative structures were verified by synthesis of the authentic gibberellins. These gibberellins were then assigned trivial numbers, e.g. 1alpha-hydroxy GA(20) (GA(118)), 1alpha-hydroxy GA(9) (GA(119)), 1,2-didehydro GA(9) (GA(120)), 1,2-didehydro GA(70) (GA(121)), 1,2-didehydro GA(69) (GA(122)) and 1,2-didehydro GA(77) (GA(126)). GA(118) and GA(119) were the first 1alpha-hydroxy gibberellins identified from higher plants. The above profile of 1,2-didehydro gibberellins suggests that 1,2-dehydrogenation might occur prior to 3beta-hydroxylation in biosynthesis of GA(3), GA(30) and GA(87) in immature seeds of P. persica.

Synthesis and confirmation of structure for a new gibberellin, 2 beta-hydroxy-GA12 (GA110), from spinach and oil palm.

The identity of a new gibberellin (GA) in spinach and oil palm sap has been confirmed as 2 beta-hydroxy-GA12 (GA110) by comparisons of GC-mass spectral data obtained for the trimethylsilyl ether methyl ester derivatives with those of a synthetic sample prepared by means of a 24 step sequence from gibberellic acid; 2 beta-hydroxy-GA24 was also prepared. Experimental details for the latter part of the syntheses are described.

Identification of three C20-gibberellins: GA97 (2 beta-hydroxy-GA53), GA98 (2 beta-hydroxy-GA44) and GA99 (2 beta-hydroxy-GA19).

Three new C20-gibberellins, GA97 (2 beta-hydroxy-GA53), GA98 (2 beta-hydroxy-GA44) and GA99 (2 beta-hydroxy-GA19), have all been isolated from spinach, GA97 also from tomato root cultures and pea pods, and GA98 from maize pollen. The structures of these compounds were established by GC-mass spectrometric comparisons of the trimethylsilylated methyl esters with authentic samples prepared from gibberellic acid (GA3).

Gibberellins in Relation to Growth and Flowering in Pharbitis nil Chois.

Flowering can be modified by gibberellins (GAs) in Pharbitis nil Chois. in a complex fashion depending on GA type, dosage, and the timing of treatment relative to a single inductive dark period. Promotion of flowering occurs when GAs are applied 11 to 17 hours before a single inductive dark period. When applied 24 hours later the same GA dosage is inhibitory. Thus, depending on their activity and the timing of application there is an optimum dose for promotion of flowering by any GA, with an excessive dose resulting in inhibition. Those GAs highly promotory for flowering at low doses are also most effective for stem elongation (2,2-dimethyl GA(4) >> GA(32) > GA(3) > GA(5) > GA(7) > GA(4)). However, the effect of GAs on stem elongation contrasts markedly with that on flowering. A 10- to 50-fold greater dose is required for maximum promotion of stem elongation, and the response is not influenced by time of application relative to the inductive dark period. These differing responses of flowering and stem elongation raise questions about the use of relatively stable, highly bioactive GAs such as GA(3) to probe the flowering response. It is proposed that the ;ideal' GAs for promoting flowering may be highly bioactive but with only a short lifetime in the plant and, hence, will have little or no effect on stem elongation.

Gibberellin Metabolism in Intact Plants of Raphanus sativus L.

The metabolism of gibberelline (GAs) in intact plants of Raphanus sativus was investigated. With [(2)H]GA feeds, [(2)H]GA1 from [(2)H]GA4, and [(2)H]GA4 and [(2)H]GA20 from [(2)H]GA9 were metabolized. Since [(2)H]GA20 was not converted into [(2)H]GA1, endogenous GA1 may have been biosynthesized from GA9 via GA4 rather than from GA20. The radioactivity of [(3)H]GA9 and [(3)H]GA20 was much more strongly transported among the plant organs than that of [(3)H]GA1 and [(3)H]GA4.

Gibberellin structure and florigenic activity in Lolium temulentum, a long-day plant.

Structural requirements for florigenic activity among gibberellins (GAs) and GA derivatives, including several new ones, applied once to leaves of Lolium temulentum, were examined. The compounds were applied to plants kept either in non-inductive short days (SD) or exposed to one inductive long day (LD). Inflorescence initiation and stem-elongation responses were assessed three weeks later. Among the GAs used, the range in effective dose for inflorescence initiation was more than 1000-fold, but substantially less for stem elongation. Some GAs promoted both stem elongation and inflorescence initiation, some promoted one without the other, and some affected neither. The structural features enhancing florigenic activity were often different from those enhancing stem elongation. Except in the case of 2,2-dimethyl GA4, a double bond in the A ring at either C-1,2 or C-2,3 was essential for high florigenic activity, though not for stem elongation. A free carboxy group was needed for both. Inflorescence initiation in Lolium was enhanced by hydroxylation at C-12, -13 and -15, whereas hydroxylation at C-3 reduced the effect on inflorescence initiation but increased that on stem elongation. A 12ß-hydroxyl was more effective than the α epimer for inflorescence initiation whereas the reverse was true for stem elongation. Although such differential effectiveness of GAs for inflorescence initiation and for stem elongation could reflect differences in uptake, transport or metabolism, we suggest that it is indicative of specific structural requirements for inflorescence initiation.

Identification of endogenous gibberellins from sorghum.

Gibberellins (GA) A(1), A(19), and A(20) were identified in shoot cylinders containing the apical meristems from sorghum (Sorghum bicolor L.). Extracts were purified by sequential SiO(2) partition chromatography and reversed-phase C(18) high performance liquid chromatography and biologically active (dwarf rice cv Tan-ginbozu microdrop assay) fractions were subjected to gas chromatography-selected ion monitoring. Based on the use of [(3)H]GA and [(2)H](d(2))GA internal standards, amounts of GA(1), GA(19), and GA(20) were estimated to be 0.7, 8.8, and 1.5 namograms per gram dry weight of tissue, respectively.

Gibberellins, Endogenous and Applied, in Relation to Flower Induction in the Long-Day Plant Lolium temulentum.

Changes in endogenous gibberellin-like substances (GAs) and related compounds in the shoot apices of Lolium temulentum during and after flower induction by one long day was examined for plants grown in three consecutive years. The total GA level in the shoot apical tissue was high (up to 42 micrograms per gram dry weight, or 3 x 10(-5) molar GA(3) equivalents), increasing several-fold on the day after the long day and then declining. Of the many GA-like substances present, the putative polyhydroxylated components-with HPLC retention times between those of GA(8) (three hydroxyls) and GA(32) (four hydroxyls), and accounting for about a quarter of the total GA activity-were most consistent and striking in their changes. Their level in the apices increased 3- to 5-fold on the day after the long day and then subsided. When various GAs were applied to plants in noninductive short days, flower initiation was induced by several, most notably by GA(32), GA(5), 2,2-dimethyl GA(4), GA(3), and GA(7). GA(32) was most like one long day in eliciting a strong flowering response while having little effect on stem growth, whereas GA(1) had the opposite effect. It is suggested that highly hydroxylated C-19 GAs may play a central role in the induction of flowering in this long-day plant.

Seed and 4-chloroindole-3-acetic acid regulation of gibberellin metabolism in pea pericarp.

In this study, we investigated seed and auxin regulation of gibberellin (GA) biosynthesis in pea (Pisum sativum L.) pericarp tissue in situ, specifically the conversion of [14C]GA19 to [14C]GA20. [14C]GA19 metabolism was monitored in pericarp with seeds, deseeded pericarp, and deseeded pericarp treated with 4-chloroindole-3-acetic acid (4-CI-IAA). Pericarp with seeds and deseeded pericarp treated with 4-CI-IAA continued to convert [14C]GA19 to [14C]GA20 throughout the incubation period (2-24 h). However, seed removal resulted in minimal or no accumulation of [14C]GA20 in pericarp tissue. [14C]GA29 was also identified as a product of [14C]GA19 metabolism in pea pericarp. The ratio of [14C]GA29 to [14C]GA20 was significantly higher in deseeded pericarp (with or without exogenous 4-CI-IAA) than in pericarp with seeds. Therefore, conversion of [14C]GA20 to [14C]GA29 may also be seed regulated in pea fruit. These data support the hypothesis that the conversion of GA19 to GA20 in pea pericarp is seed regulated and that the auxin 4-CI-IAA can substitute for the seeds in the stimulation of pericarp growth and the conversion of GA19 to GA20.

Genetic Regulation of Development in Sorghum bicolor: V. The ma(3) Allele Results in Gibberellin Enrichment.

Sorghum bicolor genotypes, near isogenic with different alleles at the third maturity locus, were compared for development, for responsiveness to GA(3) and a GA synthesis inhibitor, and occurrence and concentrations of endogenous GAs, IAA, and ABA. At 14 days the genotype 58M (ma(3) (R)ma(3) (R)) exhibited 2.5-fold greater culm height, 1.75-fold greater total height, and 1.38-fold greater dry weight than 90M (ma(3)ma(3)) or 100M (Ma(3)Ma(3)). All three genotypes exhibited similar shoot elongation in response to GA(3), and 58M showed GA(3)-mediated hastening of floral initiation when harvested at day 18 or 21. Both 90M and 100M had exhibited hastening of floral initiation by GA(3) previously, at later application dates. Tetcyclacis reduced height, promoted tillering, and delayed flowering of 58M resulting in plants which were near phenocopies of 90M and 100M. Based on bioassay activity, HPLC retention times, cochromatography with (2)H(2)-labeled standards on capillary column GC and matching mass spectrometer fragmentation patterns (ions [m/z] and relative abundances), GA(1), GA(19), GA(20), GA(53), and GA(3) were identified in extracts of all three genotypes. In addition, based on published Kovats retention index values and correspondence in ion masses and relative abundances, GA(44) and GA(17) were detected. Quantitation was based on recovery of coinjected, (2)H(2)-labeled standards. In 14 day-old-plants, total GA-like bioactivity and GA(1) concentrations (nanograms GA/gram dry weight) were two- to six-fold higher in 58M than 90M and 100M in leaf blades, apex samples, and whole plants while concentrations in culms were similar. Similar trends occurred if data were expressed on a per plant basis. GA(1) concentrations for whole plants were about two-fold higher in 58M than 90M and 100M from day 7 to day 14. Concentrations of ABA and IAA did not vary between the genotypes. The results indicate the mutant allele ma(3) (R) causes a two- to six-fold increase in GA(1) concentrations, does not result in a GA-receptor or transduction mutation and is associated with phenotypic characteristics that can be enhanced by GA(3) and reduced by GA synthesis inhibitor. These observations support the hypothesis that the allele ma(3) (R) causes an overproduction of GAs which results in altered leaf morphology, reduced tillering, earlier flowering, and other phenotypic differences between 58M and 90M or 100M.

A mutant gene that increases gibberellin production in brassica.

A single gene mutant (elongated internode [ein/ein]) with accelerated shoot elongation was identified from a rapid cycling line of Brassica rapa. Relative to normal plants, mutant plants had slightly accelerated floral development, greater stem dry weights, and particularly, increased internode and inflorescence elongation. The application of the triazole plant growth retardant, paclobutrazol, inhibited shoot elongation, returning ein to a more normal phenotype. Conversely, exogenous gibberellin A(3) (GA(3)) can convert normal genotypes to a phenotype resembling ein. The content of endogenous GA(1) and GA(3) were estimated by gas chromatography-selected ion monitoring using [(2)H]GA(1), as a quantitative internal standard and at day 14 were 1.5- and 12.1-fold higher per stem, respectively, in ein than in normal plants, although GA concentrations were more similar. The endogenous levels of GA(20) and GA(1), and the rate of GA(19) metabolism were simultaneously analyzed at day 7 by feeding [(2)H(2)]GA(19) and measuring metabolites [(2)H(2)]GA(20) and [(2)H(2)]GA(1) and endogenous GA(20) and GA(1), with [(2)H(5)]GA(20) and [(2)H(5)]GA(1) as quantitative internal standards. Levels of GA(1) and GA(20) were 4.6- and 12.9-fold higher, respectively, and conversions to GA(20) and GA(1) were 8.3 and 1.3 times faster in ein than normal plants. Confirming the enhanced rate of GA(1) biosynthesis in ein, the conversion of [(3)H]GA(20) to [(3)H]GA(1) was also faster in ein than in the normal genotype. Thus, the ein allele results in accelerated GA(1) biosynthesis and an elevated content of endogenous GAs, including the dihydroxylated GAs A(1) and A(3). The enhanced GA production probably underlies the accelerated shoot growth and development, and particularly, the increased shoot elongation.

Isolation and identification of antheridiogens in the ferns, Lygodium microphyllum and Lygodium reticulatum.

Antheridiogens in culture media of 6-week-old prothallia of two species of Schizaeaceous ferns, Lygodium microphyllum and Lygodium reticulatum, were analyzed by gas chromatography-mass spectrometry. In both species, the gibberellin A73 methyl ester (GA73-Me) was identified as the most abundant antheridiogen, and the methyl esters of GA9 and of several monohydroxy-GA73 derivatives were also detected. Since both species produced antheridiogens at a high level, they were classified into high-antheridiogen-producing ferns. The response to GA73-Me of gametophytes of both species is also discussed.

Gibberellins and Antheridiogens in Prothallia and Sporophytes of Anemia phyllitidis.

The following gibberellins (GAs) and antheridiogens were identified by their mass spectra and Kovats retention indices from combined gas chromatography-mass spectrometry of purified extracts of the prothallia and sporophytes of Anemia phyllitidis, a Schizaeaceous fern: a trace amount of GA9 (4-week-old prothallia); GA9, GA24, GA25, antheridic acid and 3-epi-GA63 (6-week-old prothallia); and GA4, GA9, GA15, GA19, GA20, and GA24 [young sporophytes (younger than one year old) and/or old sporophytes (between one- and two years old). Of these compounds, GA24, GA9, and GA4 were quantified by gas chromatography-selected ion monitoring, using (2)H-GAs as internal standards, and the content of antheridic acid, the principal antheridiogen, was evaluated by a radioimmunoassay which we have developed. The results indicate that endogenous levels of GAs and antheridiogens in prothallia began to increase rapidly between 4 and 6 weeks after sowing, the contents of antheridic acid and GA24, the most abundant GA in 6-week-old prothallia, being 107.4 and 37.9 ng/g fresh weight, respectively. The most abundant GA in the sporophytes was GA9, the content in young and old sporophytes being 15.3 and 7.3 ng/g fresh weight, respectively.

Identification of Gibberellins and 9,15-Cyclogibberellins in Developing Apple Seeds.

Endogenous gibberellins (GAs) and GA-related compounds at two different developmental stages of apple seeds(Malus domestica cv. McIntosh) were analyzed by gas chromatography-mass spectrometry.From the seeds at ca. 10 and/or 14 weeks after full-bloom, the following GAs and 9,15-cyclogibberellins (9,15-cyclo-GAs) were identified by a comparison of their mass spectra and Kovats retention indices with those of authentic specimens: GA4, GA7, GA9, GA12, GA17, GA19, GA20, GA25, GA34, GA35, GA45,GA53, GA54, GA61, GA62, GA63, GA70, GA73, GA80, GA84, GA88, 3-epi-GA4, 3-epi-GA54, and 3-epi-GA63, 9,15-cyclo-GA9, lß-hydroxy-9,15-cyclo-GA9, 2ß-hydroxy-9,15-cyclo-GA9, 3α-hydroxy-9,15- cyclo-GA9, 3ß-hydroxy-9,15-cyclo-GA9, and llß-hydroxy-9,15-cyclo-GA9. The major components in the seeds at ca. 10 weeks after full-bloom were GA4, GA7, GA9, GA17, GA35, GA54, GA62, GA80, and GA84, and those in the seeds at ca. 14 weeks after full-bloom were GA17, GA25, GA45, GA62, GA63, GA80,GA84, 9,15-cyclo-GA9, and 1ß-, 3ß-, and 11ß-hydroxy-9,15-cyclo-GA9. New GA number (GA103 _ 108) have been allocated to 9,15-cyclo-GA9, and 1ß-, 2ß-, 3ß-, 3α-, and 11ß-,hydroxy-9,15-cyclo-GA9, respectively (1ß- and 3α-hydroxy-9,15-cyclo-GA9 were identified previously as fern anteridiogens, although GA numbers have not previously been assigned to these compounds). This is the first report of the co-occurrence of GA73 and 9,15-cyclo-GAs in higher plants.