Gibberellin A(3) Is Biosynthesized from Gibberellin A(20) via Gibberellin A(5) in Shoots of Zea mays L

[17-¹³C,³H]-Labeled gibberellin A₂₀ (GA₂₀), GA₅, and GA₁ were fed to homozygous normal (+/+), heterozygous dominant dwarf (D8/+), and homozygous dominant dwarf (D8/D8) seedlings of Zea mays L. (maize). ¹³C-Labeled GA₂₉, GA₈, GA₅, GA₁, and 3-epi-GA₁, as well as unmetabolized [¹³C]GA₂₀, were identified by gas chromatography-selected ion monitoring (GC-SIM) from feeds of [17-¹³C, ³H]GA₂₀ to all three genotypes. ¹³C-Labeled GA₈ and 3-epi-G₁, as well as unmetabolized [¹³C]GA₁, were identified by GC-SIM from feeds of [17-¹³C, ³H]GA₁ to all three genotypes. From feeds of [17-¹³C, ³H]GA₅, ¹³C-labeled GA₃ and the GA₃-isolactone, as well as unmetabolized [¹³C]GA₅, were identified by GC-SIM from +/+ and D8/D8, and by full scan GC-MS from D8/+. No evidence was found for the metabolism of [17-¹³C, ³H]GA₅ to [¹³C]GA₁, either by full scan GC-mass spectrometry or by GC-SIM. The results demonstrate the presence in maize seedlings of three separate branches from GA₂₀, as follows: (a) GA₂₀ → GA₁ → GA₈; (b) GA₂₀ → GA₅ → GA₃; and (c) GA₂₀ → GA₂₉. The in vivo biogenesis of GA₃ from GA₅, as well as the origin of GA₅ from GA₂₀, are conclusively established for the first time in a higher plant (maize shoots).     

Metabolism of kaurenoids by Gibberella fujikuroi in the presence of the plant growth retardant,N,N,N-trimethyl-1-methyl-(2′,6′,6′-trimethylcyclohex-2′-en-1′-yl)prop-2-enylammonium iodide

The plant growth retardant, N,N,N-trimethyl-1-methyl-(2′,6′,6′-trimethylcyclohex-2′-en-1′-yl)prop-2-enylammonium iodide, is shown to block gibberellin biosynthesis in Gibberella fujikuroi between mevalonate and ent-kaur-16-ene, probably by inhibiting ent-kaur-16-ene synthetase A-activity. In the presence of the plant growth retardant, cultures of the fungus incorporate (26.5%) added ent-[¹⁴C]-kaur-16-ene into gibberellin A₃. Under the same conditions kaur-16-ene, 13β-kaur-16-ene, and ent-kaur-15-ene are not metabolised to gibberellin analogues.     

The endogenous gibberellins of dwarf mutants of lettuce

The gibberellin (GA) content of E-1, a tall genotype of early flowering lettuce (Lactuca sativa L.), and of three selected GA-responsive dwarfs, dwf1, dwf2, and dwf2¹, has been determined using ¹³C-labeled internal standards and gas chromatographymass spectrometry (GC-MS). In the shoots of the E-1 parent, GA₁, 3-epi-GA₁, GA₃, GA₅, GA₈, GA₁₉, GA₂₀, GA₂₉, and GA₅₃ were identified by full scan GC-MS and Kovats retention indices. Purification by immunoaffinity chromatography selective for 13-hydroxy GAs, was necessary for GA identification. Relative to the parent E-1, the concentrations of GA₁, GA₈, GA₂₀, and GA₂₉ in the shoots of dwf2 plants were reduced to about 10% and in shoots of dwf2¹ plants to less than 50%. In dwf1 the levels of GA₁, GA₈, and GA₂₉ were also reduced to less than 50% of the parent E-1, but the level of GA₂₀ was fivefold higher than in E-1. Plant height was correlated with the endogenous levels of GA₁ and GA₈.     

Qualitative and Quantitative Analyses of Gibberellins in Vegetative Shoots of Normal, dwarf-1, dwarf-2, dwarf-3, and dwarf-5 Seedlings of Zea mays L

Gibberellins A₁₂ (GA₁₂), GA₅₃, GA₄₄, GA₁₉, GA₁₇, GA₂₀, GA₂₉, GA₁, and GA₈ have been identified from extracts of vegetative shoots of normal (wild type) maize using full scan capillary gas chromatography-mass spectrometry and Kovats retention indices. Seven of these gibberellins (GAs) have been quantified by capillary gas chromatography-selected ion monitoring using internal standards of [¹⁴C₄]GA₅₃, [¹⁴C₄]GA₄₄, [²H₂] GA₁₉, [¹³C₁]GA₂₀, [¹³C₁]GA₂₉, [¹³C₁]GA₁, and [¹³C₁]GA₈. Quantitative data from extracts of normal, dwarf-1, dwarf-2, dwarf-3, and dwarf-5 seedlings support the operation of the early 13-hydroxylation pathway in vegetative shoots of Zea mays. These data support the positions in the pathway blocked by the mutants, previously assigned by bioassay data and metabolic studies. The GA levels in dwarf-2, dwarf-3, and dwarf-5 were equal to, or less than, 2.0 nanograms per 100 grams fresh weight, showing that these mutants are blocked for steps early in the pathway. In dwarf-1, the level of GA₁ was very low (0.23 nanograms per 100 grams fresh weight) and less than 2% of that in normal shoots, while GA₂₀ and GA₂₉ accumulated to levels over 10 times those in normals; these results confirm that the dwarf-1 mutant blocks the conversion of GA₂₀ to GA₁. Since the level of GAs beyond the blocked step for each mutant is greater than zero, each mutated gene probably codes for an altered gene product, thus leading to impaired enzyme activities.     

Position of the metabolic block for gibberellin biosynthesis in mutant b1-41a of Gibberella fujikuroi

Mutant B1-41a, obtained by UV-irradiation of Gibberella fujikuroi strain GF-1a, does not metabolise mevalonic acid lactone (MVL), ent-kaur-16-ene, ent-kaurenol, and ent-kaurenal to gibberellins. ent-Kaur-16-ene-19-oic acid is completely metabolised to give the same gibberellins in similar concentration as unsupplemented cultures of the parent strain. It is concluded that this mutant is blocked for gibberellin synthesis at the step from ent-kaurenal to ent-kaurenoic acid. Comparison of the incorporation of MVL into GA₃ by the mutant and the parent strains indicate that the metabolic block is 97·5% effective. A method of preparing ent-kaur-16-ene, labelled at C-15 and C-17 by [²H] and [³H] is described.     

Conversion of [14C]gibberellin A12-aldehyde to C19- and C20-gibberellins in a cell-free system from immature seed of Phaseolus coccineus L.

A cell-free system prepared from developing seed of runner bean (Phaseolus coccineus L.) converted [¹⁴C]gibberellin A₁₂-aldehyde to several products. Thirteen of these were identified by capillary gas chromatography-mass spectrometry as gibberellin A₁ (GA₁), GA₄, GA₅, GA₆, GA₁₅, GA₁₇, GA₁₉, GA₂₀, GA₂₄, GA₃₇, GA₃₈, GA₄₄ and GA₅₃-aldehyde, all giving mass spectra with ¹⁴C-isotope peaks. GA₈ and GA₂₈ were also identified but contained no ¹⁴C. All the [¹⁴C]GA₁₂-aldehyde metabolites, except GA₁₅, GA₂₄ and GA₅₃-aldehyde, are known endogenous GAs of P. coccineus.Abbreviations GA_n gibberellin A_n - GC-MS combined gas chromatography-mass spectrometry - HPLC highperformance liquid chromatography - MVA mevalonic acid - S-2 2000-g supernatant     

Biosynthesis of gibberellins A12, A15, A24, A36, and A37 by a cell-free system from Cucurbita maxima

GA₁₂-aldehyde obtained from mevalonate via ent-kaurene, ent-kaurenol, ent-kaurenoic acid and ent-7α-hydroxykaurenoic acid in a cell-free system from immature seeds of Cucurbita maxima was converted to GA₁₂ by the same system. When Mn²⁺ was omitted from the system GA₁₂-aldehyde and GA₁₂ were converted further to several products. Among these GA₁₅, GA₂₄, GA₃₆ and GA₃₇ were conclusively identified by GC-MS. With the exception of GA₃₇ these GAs have not previously been found in higher plants. Another biosynthetic pathway led from ent-7α-hydroxykaurenoic acid to very polar products via what was tentatively identified as ent-6α, 7α-dihydroxykaurenoic acid. An unidentified component with an MS resembling that of a dihydroxykaurenolide was also obtained from incubations with mevalonate.     

Metabolism of ent-kaurenol-[17-14C], ent-kaurenal-[17-14C] and ent-kaurenoic acid-[17-14C] by germinating Hordeum distichon grains

Subcellular fractions from germinated barley embryos, chloroplast preparations and whole germinating barley grains are able to carry out the conversions ent-kaurenol → ent-kaurenal → ent-kaurenoic acid → ent-hydroxykaurenoic acid, the initial steps of the biosynthetic pathway to gibberellins. Whole grains, and chloroplasts to a slight extent, incorporate radioactivity from ent-kaurenol-[17-¹⁴C] and ent-kaurenoic acid-[17-¹⁴C] into materials with similar but distinct properties from the gibberellins GA₁, GA₃, GA₄ and GA₇.     

Function and Substrate Specificity of the Gibberellin 3β-Hydroxylase Encoded by the Arabidopsis GA4 Gene

cDNA corresponding to the GA4 gene of Arabidopsis thaliana L. (Heynh.) was expressed in Escherichia coli, from which cell lysates converted [¹⁴C]gibberellin (GA)₉ and [¹⁴C]GA₂₀ to radiolabeled GA₄ and GA₁, respectively, thereby confirming that GA4 encodes a GA 3β-hydroxylase. GA₉ was the preferred substrate, with a Michaelis value of 1 μm compared with 15 μm for GA₂₀. Hydroxylation of these GAs was regiospecific, with no indication of 2β-hydroxylation or 2,3-desaturation. The capacity of the recombinant enzyme to hydroxylate a range of other GA substrates was investigated. In general, the preferred substrates contained a polar bridge between C-4 and C-10, and 13-deoxy GAs were preferred to their 13-hydroxylated analogs. Therefore, no activity was detected using GA₁₂-aldehyde, GA₁₂, GA₁₉, GA₂₅, GA₅₃, or GA₄₄ as the open lactone (20-hydroxy-GA₅₃), whereas GA₁₅, GA₂₄, and GA₄₄ were hydroxylated to GA₃₇, GA₃₆, and GA₃₈, respectively. The open lactone of GA₁₅ (20-hydroxy-GA₁₂) was hydroxylated but less efficiently than GA₁₅. In contrast to the free acid, GA₂₅ 19,20-anhydride was 3β-hydroxylated to give GA₁₃. 2,3-Didehydro-GA₉ and GA₅ were converted by recombinant GA4 to the corresponding epoxides 2,3-oxido-GA₉ and GA₆.Dwarf mutants with reduced biosynthesis of the GA plant hormones have been valuable tools in studies of the function of these compounds (Ross, 1994). In Arabidopsis thaliana, mutations at six loci (GA1-GA6) that result in reduced GA biosynthesis have been identified (Koorneef and van der Veen, 1980; Sponsel et al., 1997), and three of these loci have recently been cloned. The GA1 locus was isolated by genomic subtraction (Sun et al., 1992) and shown by heterologous expression in Escherichia coli to encode the enzyme that cyclizes geranylgeranyl diphosphate to copalyl diphosphate (Sun and Kamiya, 1994). This enzyme was formerly referred to as ent-kaurene synthase A but has been renamed copalyl diphosphate synthase (Hedden and Kamiya, 1997; MacMillan, 1997). The GA5 locus was shown to correspond to one of the GA 20-oxidase genes (Xu et al., 1995), the products of which catalyze the conversion of GA₁₂ to GA₉ and GA₅₃ to GA₂₀ (Phillips et al., 1995; Xu et al., 1995). GA 20-oxidases are 2-oxoglutarate-dependent dioxygenases that are encoded by small multigene families, members of which are differentially expressed in plant tissues (Phillips et al., 1995; Garcia-Martinez et al., 1997).The GA4 locus was isolated by T-DNA tagging and, on the basis of the derived amino acid sequence, was also shown to encode a dioxygenase (Chiang et al., 1995). Several lines of evidence indicate that the GA4 gene encodes a GA 3β-hydroxylase. Shoots of a ga4 mutant, all alleles of which are semidwarf, contained reduced concentrations of the 3β-hydroxy GAs GA₁, GA₄, and GA₈ compared with the Landsberg erecta wild type, whereas levels of immediate precursors to these GAs were elevated (Talon et al., 1990). Furthermore, metabolism of [¹³C]GA₂₀ to [¹³C]GA₁ was substantially less in the mutant than in the wild type (Kobayashi et al., 1994). In the present paper we confirm by functional expression of its cDNA in E. coli that GA4 encodes a GA 3β-hydroxylase. In addition, we determine the substrate specificity of recombinant GA4 using a number of C₂₀- and C₁₉-GAs and show by kinetic analysis that the enzyme has a higher affinity for GA₉ than for GA₂₀, which is consistent with the non-13-hydroxylation pathway predominating in Arabidopsis (Talon et al., 1990).     

Metabolism of Gibberellin A(12) and A(12)-Aldehyde in Developing Seeds of Pisum sativum L

Metabolism of [¹⁴C]gibberellin (GA) A₁₂ (GA₁₂) and [¹⁴C]gibberellin A₁₂-aldehyde (GA₁₂-aldehyde) was examined in cotyledons and seed coats from developing seeds of pea (Pisum sativum L.). Both were metabolized to only 13-hydroxylated GAs in cotyledons but to 13-hydroxylated and non-13-hydroxylated GAs in seed coats. The metabolism of [¹⁴C]GA₁₂ was slower in seed coats than in cotyledons. [¹⁴C]GA₁₂-aldehyde was also metabolized to conjugates in seed coats. Seed coat [¹⁴C]-metabolites produced from [¹⁴C]GA₁₂-aldehyde were isolated by high-performance liquid chromatography (HPLC). Conjugates were base hydrolyzed and the free GAs reisolated by HPLC and identified by gas chromatography-mass spectrometry. [¹⁴C]GA₅₃-aldehyde, [¹⁴C]GA₁₂-aldehyde conjugate, and [¹⁴C]GA₅₃-aldehyde conjugate were major metabolites produced from [¹⁴C]GA₁₂-aldehyde by seed coats aged 20-22 days or older. The dilution of ¹⁴C in these compounds by ¹²C, as compared to the supplied [¹⁴C]GA₁₂-aldehyde, indicated that they are endogenous. Feeding [¹⁴C]GA₅₃-aldehyde led to the production of [¹⁴C]GA₅₃-aldehyde conjugate in seed coats and shoots and also to 13-hydroxylated GAs in shoots. Labeled GAs, recovered from plant tissue incubated with either [¹⁴C]GA₁₂, [¹⁴C]GA₁₂-aldehyde, or [³H]GA₉, were used as appropriate markers for the recovery of endogenous GAs from seed coats or cotyledons. These GAs were purified by HPLC and identified and quantified by gas chromatography-mass spectrometry. GA₁₅, GA₂₄, GA₉, GA₅₁, GA₅₁-catabolite, GA₂₀, GA₂₉, and GA₂₉-catabolite were detected in seed coats, whereas GA₉, GA₅₃, GA₄₄, GA₁₉, GA₂₀, and GA₂₉ were found in cotyledons. The highest GA levels were for GA₂₀ and GA₂₉ in cotyledons (783 and 912 nanograms per gram fresh weight, respectively) and for GA₂₉ and GA₂₉-catabolite in seed coats (1940 and > 1940 nanograms per gram fresh weight, respectively).     

Conversion of gibberellin A14 to other gibberellins in seedlings of dwarf Pisum sativum

Gibberellin A₁₄-[17-³H] applied to seedlings of dark grown dwarf pea (Pisum sativum L. cy. Meteor) was converted to GA₁, GA₈, GA₁₈, GA₂₃, GA₂₈, and GA₃₈. The sequence of interconversion of GA₁₄→ GA₁₈ → GA₃₈ → GA₂₃ → GA₁ → GA₈ is indicated. Identifications were made by gas-liquid radiochromatography using three liquid stationary phases.     

Native gibberellins and the metabolism of [14C]gibberellin A53 and of [17-13C, 17-3H2]gibberellin A20 in tassels of Zea mays

The native hormones from tassels of maize (Zea mays) were re-investigated. The previous identification by GC/SIM of GA₁, GA₈ and GA₂₉ in normal tassels was confirmed by full GC/MS scans at the correct Kovats retention indices. In tassels of dwarf-1 mutants, GA₄₄,^?GA₁₉, GA₁₇, GA₂₀ and the 16,17-dihydro, 7β,16α,17-trihydroxy derivative of ent-kaurenoic acid were identified by GC/MS. Gibberellin A₁ was not found in the mutant tassels. [¹⁴C]Gibberellin A₅₃ was fed to tassels of the dwarf-5 mutant. In the ethyl acetate-soluble acidic fraction from the feeds, [¹⁴C]GA₄₄ was identified by GC/MS; [¹⁴C]GA₁₉ and [¹⁴C]GA₂₉ were identified by GC/SIM. The GA₂₉ is probably a metabolite of the feeds because the dwarf-5 mutant is known to control the step copalyl pyrophosphate to ent-kaurene in the maize GA-biosynthetic pathway and because GA₂₉ was not identified in a control experiment. The n-butanol fractions obtained from the feeds were shown, by GC/MS, to contain [¹⁴C]GA₅₃ after hydrolysis, suggesting that conjugated [¹⁴C]GA₅₃ is a major metabolite from GA₅₃ feeds. [17-¹³C, 17-³H₂]Gibberellin A₂₀ was fed to normal, dwarf-1 and dwarf-5 tassels. In each case, analysis of the purified ethyl acetate-soluble acidic extracts by GC/MS led to the identification of [¹³C]GA₂₉ and unmetabolized [¹³C]GA₂₀ in which no ¹³C-isotope dilution was observed.     

Purification and partial characterization of a gibberellin 2β-hydroxylase fromPhaseolus vulgaris

A gibberellin 2β-hydroxylase has been purified from mature seeds ofPhaseolus vulgaris. The enzyme is of molecular weight 36,000 and has the characteristics of a dioxygenase; the cofactors areα-ketoglu-tarate, Fe²⁺ and ascorbate, and activity is stimulated by catalase. The V_max of the enzyme is 6.86 nmole h^?1 mg^?1, and the Km values for [1,2-³H₂]GA₁ andα-ketoglutarate are 0.085 μM and 21 μM, respectively. The purified enzyme preparation catalyzes hydroxylation of GA₁, GA₄, GA₉, and GA₂₀ but exhibits a marked preference for the 3-hydroxylated gibberellins as substrate.     

Endogenous Gibberellins in Elongating Shoots of Clones of Salix dasyclados and Salix viminalis

Elongating shoots of rapidly growing clones of Salix viminalis L. (clone 683-4) and Salix dasyclados Wimm. (clone 908) harvested in early August were analyzed for endogenous gibberellins (GA). Distribution of GA-like activity, determined by Tan-ginbozu dwarf rice microdrop bioassay after reverse phase C₁₈ high performance chromatography, was similar for both species. For S. dasyclados, combined gas chromatography-selected ion monotoring (GC-SIM) yielded identifications of GA₁, GA₈, GA₁₉, GA₂₀, and GA₂₉. Identifications of GA₄ and GA₉ were also made using co-injections of known amounts of [17, 17-²H₂]GAs. By bioassay, the main activity was GA₁₉-like in both species. Gibberellin A₁, GA₁₉, and GA₂₀ concentrations were approximated by GC-SIM using co-injections of known amounts of [17,17-²H₂]GAs. Both bioassay and GC-SIM results indicated very high concentrations of GA₁₉ and GA₂₀ (about 6000 nanograms per kilogram fresh weight shoot tissue using GC-SIM: 800 ng using bioassay), compared to the concentration of GA₁ (about 130 nanograms per kilogram fresh weight using either GC-SIM or bioassay).     

Gibberellin A(1) Biosynthesis in Pisum sativum L. : II. Biological and Biochemical Consequences of the le Mutation

A comparative study of the metabolism of radiolabeled gibberellin (GA) 1, 19, and 20 in isolated vegetative tissues of isogenic Le and le pea (Pisum sativum) plants incubated in vitro with the appropriate GA substrate is described. The results of this study provide evidence that the enzymes involved in the latter stages of GA biosynthesis are spatially separated within the growing pea plant. Apical buds were not apparently involved in the production of bioactive GA₁ or its immediate precursors. The primary site of synthesis of GA₂₀ from GA₁₉ was immature leaflets and tendrils, and the synthesis of bioactive GA₁ and its inactive catabolite GA₈ occurred predominantly in stem tissue. GA₂₉, the inactive catabolite of GA₂₀, was produced to varying extents in all the tissues examined. Little or no difference was observed in the ability of corresponding Le and le tissues to metabolize radiolabeled GA₁, GA₁₉, or even GA₂₀. During a fixed period of 24 hours, stems of plants carrying the le mutation produced slightly more [³H]GA₁ (and [³H]GA₂₉) than those of Le plants. It has been concluded that the le mutation does not lie within the gene encoding the GA₂₀ 3β-hydroxylase protein.     

Metabolism of Tritiated Gibberellins A(4) and A(9) in Norway Spruce, Picea abies (L.) Karst. : Effects of a Cultural Treatment Known to Enhance Flowering

Shoots of mature grafted propagules of Picea abies (L.) Karst. metabolized [³H]gibberellin A₄ (GA₄) to at least 14 acidic substances, two of which were tentatively identified by gas-liquid radiochromatography as GA₂ (possibly an artifact) and GA₃₄. [³H]GA₉ was converted into a number of metabolites, one of which was chromatographically similar to, but not identical with, GA₄. Metabolism was maximally 61 and 57% over 48 hours for GA₄ and GA₉, respectively, and was correlated with the rate of change (i.e. increase followed by decrease) in endogenous GA-like substances as shoot elongation progressed. Propagules covered with a clear plastic film, a treatment which promotes flowering, metabolized [³H]GA₄ more slowly than did control plants in the open. Inasmuch as a GA_4/7 mixture can also promote flowering in P. abies, the retarded metabolism of [³H]GA₄ may reflect the manner in which trees under plastic metabolize endogenous GA-like substances. If so, then the stimulating effect of this cultural treatment on flowering may come about through an increased level of endogenous, less polar GA-like substances.     

Use of an Acylcyclohexanedione Growth Retardant, LAB 198 999, to Determine Whether Gibberellin A(20) Has Biological Activity per se in Dark-Grown Dwarf (le) Seedlings of Pisum sativum

Dwarf (le⁵⁸³⁹) seedlings of Pisum sativum respond to gibberellin A₂₀ (GA₂₀) in the dark, although the same dosage of GA₂₀ applied to light-grown le⁵⁸³⁹ seedlings elicits no growth response. The acylcyclohexanedione growth retardant, LAB 198 999, which is known to inhibit gibberellin oxidation and in particular 3β-hydroxylation such as the conversion of GA₂₀ to GA₁, also inhibits the growth response of dark-grown dwarf (le⁵⁸³⁹) seedlings to GA₂₀. Thus, the biological activity of GA₂₀ in the dark appears to be a consequence of its conversion to GA₁, even though it is known from studies with light-grown seedlings that the le mutation reduces the conversion of GA₂₀ to GA₁.     

Biosynthetic Origin of Gibberellins A(3) and A(7) in Cell-Free Preparations from Seeds of Marah macrocarpus and Malus domestica

Cell-free preparations from seeds of Marah macrocarpus L. and Malus domestica L. catalyzed the conversion of gibberellin A₉ (GA₉) and 2,3-dehydroGA₉ to GA₇; GA₉ was also metabolized to GA₄ in a branch pathway. The preparation from Marah seeds also metabolized GA₅ to GA₃ in high yield; GA₆ was a minor product and was not metabolized to GA₃. Using substrates stereospecifically labeled with deuterium, it was shown that the metabolism of GA₅ to GA₃ and of 2,3-dehydroGA₉ to GA₇ occurs with the loss of the 1β-hydrogen. In cultures of Gibberella fujikuroi, mutant B1-41a, [1β,2β-²H₂]GA₄, was metabolized to [1,2-²H₂]GA₃ with the loss of the 1α- and 2α-hydrogens. These results provide further evidence that the biosynthetic origin of GA₃ and GA₇ in higher plants is different from that in the fungus Gibberella fujikuroi.     

Implication of Gibberellins in Head Smut (Sporisorium reilianum) of Sorghum bicolor

The head smut fungus, Sporisorium reilianum ([Kuhn] Landon and Fullerton), was shown to reduce plant height in infected Sorghum bicolor ([L.] Moench) plants. The major reductions occurred in the internodes nearest the panicle and were more severe in naturally infected than in inoculated plants. Less affected plants developed reproductively sterile panicles, and eventually smutted panicles developed phyllodied growths which progressed into leafy shoots. Extracts of smutted, sterile, and healthy (control) panicles of field-grown plants exhibited gibberellin (GA)-like activity in the dwarf rice bioassay. When extracts were purified and assayed with deuterium-labeled GA standards by gas chromatography-mass spectrometry-selected ion monitoring (GC-MS-SIM), GA₁, GA₃, GA₁₉, GA₂₀, and GA₅₃ were detected based on coelution with the standards, identical Kovats retention index values, and matching ion masses and relative abundances for three major ions. In addition, based on published Kovats retention index values, ion masses, and relative abundance values, GA₄, GA₇, GA₈, GA₁₄, GA₂₉, and GA₄₄ were tentatively identified. Quantitative analysis revealed that panicles of healthy control plants contained from 60 to 100% higher total concentrations of GAs than panicles of smutted plants. These comparisons were most striking for the early 13-hydroxylation pathway precursors GA₅₃, GA₄₄, and GA₁₉ but not for GA₂₀. Extracts of S. reilianum sporidia and culture medium exhibited GA-like bioactivity, and GA₁ and GA₃ were detected based on GC-MS-SIM assay with ²H-labeled internal standards. Quantitative analysis of these GAs showed increasing concentrations from 4 to 7 to 10 days of culture and a decline at 20 days. This is the first GC-MS-SIM detection of GAs in a non-Ascomycete fungus, and the disease symptoms and quantitative data suggested that fungal infection may interfere with biosynthesis of GAs by the host plant.