Relationship between Flower Induction by Benzoic Acid and its Metabolism in Lemna paucicostata 151

The flower-inducing activities in Lemna paucicostata 151 offour major metabolites of benzoic acid (N-benzoyl aspartate,benzyl 6-O-ß-D-apiofuranosyl-O-ß-D-glucopyranoside,O-benzoyl isocitrate and O-benzoyl malate) were measured, andthe effects on the uptake and metabolism of benzoic acid dueto change in the level of the benzoic acid concentration orto the addition of plant hormones were investigated. N-Benzoylaspartate had weak activity, and O-benzoyl isocitrate and malatehad fairly strong activities, while benzyl 6-O-ß-D-apiofuranosyl-ß-D-glucopyranosideshowed no activity. As the concentration of benzoic acid rose,the ratio of N-benzoyl aspartate increased and that of benzyl6-O-ß-D-apiofuranosyl-O-ß-D-glucopyranosidedecreased. GA₃ and IAA, inhibitors of flower induction by benzoicacid, seemed to promote conversion to N-benzoyl aspartate insteadof to benzyl 6-O-ß-D-apiofuranosyl-ß-D-glucopyranoside.The conversion to N-benzoyl aspartate was considered to be adetoxification process and that to benzyl 6-O-ß-D-apiofuranosyl-ß-D-glucopyranosidemay be directly related to flower induction in Lemna. (Received November 2, 1987; Accepted January 23, 1988)     

Effects of a Plant-Growth Regulator, Prohexadione, on the Biosynthesis of Gibberellins in Cell-Free Systems Derived from Immature Seeds

Inhibition of the biosynthesis of gibberellins by prohexadione,3,5-dioxo-4-propionylcyclo-hexanecarboxylic acid, was studiedwith cell-free systems derived from immature seeds of Cucur-bitamaxima, Phaseolus vulgaris and Pisum sativum. Prohexadione,at a concentration of 10–⁴ M, inhibited C-7 oxidationof GA₁₂-aldehyde, C-20 oxidation of GA₁₅, conversion of C₂₀-gib-berellinsto C₁₉-gibberellins, 3ß-hydroxylation, 2,3-dehydrogenationof GA²⁰, 2,3-epoxidation of GA₅ and 2ß-hydroxylationof GA₉ and GA₂₀. The 3ß-hydroxylase activity appearedto be more sensitive to prohexadione than were the C-20 oxygenaseand the 2ß-hydroxylase activities. The conversionof mevalonic acid to GA₁₂-aldehyde and the 13-hydroxylationof GA₁₂ were not affected by prohexadione at a concentrationof 3 ? 10^–4 M. All of the steps inhibited by prohexadioneare oxidation steps catalyzed by soluble enzymes that require2-oxoglutarate, Fe²⁺ and oxygen, and all of them occur distalto the synthesis of GA₁₂-aldehyde in the biosynthesis of gibberellins. (Received April 4, 1990; Accepted September 14, 1990)     

Control by Light of Hypocotyl Elongation and Levels of Endogenous Gibberellins in Seedlings of Lactuca sativa L.

Four 13-hydroxygibberellins, gibberellin A₁ (GA₁), 3-epi-GA₁,GA₁₉ and GA₂₀ were identified by full-scan GC/MS in extractsof lettuce seedlings (Lactuca sativa L. cv. Grand Rapids). Theresults suggest that the early-13-hydroxylation biosyntheticpathway to GA₁ functions in the lettuce seedlings. It was alsofound that GA₁ is active per se in the control of hypocotylelongation in lettuce seedlings. To investigate the relationshipbetween control by light of hypocotyl elongation and levelsof endogenous GAs in lettuce, endogenous levels of GAs werequantified by radioimmunoassay in seedlings that had been grownfor 5 days in the dark (5D) and in those that had been grownfor 4 days in the dark and then under white light for 1 day(4D1L). The endogenous level of GA₁ in the upper and lower partsof hypocotyls in 5D seedlings was about four times higher thanthat in 4D1L seedlings. The response of explants (hypocotylsegments with cotyledons) from dark-grown seedlings to GA₁ isknown to be similar in the dark and under white light when theexplants are treated with inhibitors of the biosynthesis ofGA. Therefore, the above information suggests that the highlevel of GA₁ in hypocotyls of dark-grown seedlings is responsiblefor the rapid elongation of hypocotyl, while irradiation bywhite light decreases the endogenous level of GA₁ in the hypocotylswith a resultant decrease in the rate of hypocotyl elongation. (Received March 13, 1992; Accepted May 21, 1992)     

Effects of Gibberellins on Seed Germination of Phytochrome-Deficient Mutants of Arabidopsis thaliana

Experiments were carried out to explore the involvement of gibberellins(GAs) in the light-induced germination of Arabidopsis thaliana(L.) Heynh, using wild type (WT) and phytochrome-deficient mutants(phyA, phyB and phyAphyB deficient in phytochrome A, B and Aplus B, respectively). Seed germination of WT and phytochrome-deficientmutants was inhibited by uniconazole (an inhibitor of an earlystep in biosynthesis of GA, the oxidation of ent-kaurene) andprohexadione (an inhibitor of late steps, namely, 2rß-and 3rß-hydroxylation). This inhibition was overcomeby simultaneous application of 10^-5 M GA₄. The relative activityof GAs for promoting germination of uniconazole-treated seedswas GA₄>GA₁=GA₉>GA₂₀. The wild type and the phyA and phyBmutants had an increased response to a red light pulse in thepresence of GA₁, GA₄, GA₉, GA₂₀ and GA₂₄ but there were no significantdifferences in activity of each GA between the mutants. Therefore,neither phytochrome A nor hytochrome B appears to regulate GAbiosynthesis from GA₁₂ to GA₄ during seed germination, sincethe conversion of GA₁₂ to GA₉ is regulated by one enzyme (GA20-oxidase). However, GA responsiveness appears to be regulatedby phytochromes other than phytochromes A and B, since the phyAphyBdouble mutant retains the photoreversible increased responseto GAs after a red light pulse. (Received February 13, 1995; Accepted July 11, 1995)     

Effects of Deoxygibberellin C (DGC) and 16-Deoxo-DGC on Gibberellin 3{beta}-Hydroxylase and Plant Growth

Deoxygibberellin C (DGC), a C/D ring-rearranged isomer of GA₂₀,was shown to inhibit the conversion of [2,3-³H₂]GA₉ to [2-³H]GA₄by gibberellin 3ß-hydroxylase from immature seedsof Phaseolus vulgahs. Deoxygibberellin C inhibited the promotionof growth by exogenously applied GA₂₀ of rice (Oryza sativaL.) seedlings. Evidence is also presented that DGC is a competitiveinhibitor of the 3ß-hydroxylase from P. vulgaris.However, DGC only weakly inhibited the conversion catalyzedby the 3ß-hydroxylase from Cucurbita maxima at highconcentrations, and it did not inhibit the promotion of growthby exogenously applied GA₉ of cucumber (Cucumis sativus) seedlings.These results suggest that the 3ß-hydroxylases fromP. vulgaris and C. maxima have different structural requirementswith respect to their substrates. 16-Deoxo-DGC also inhibitedcatalysis of the same conversion by 3ß-hydroxylasefrom P. vulgaris, and it slightly inhibited the conversion catalyzedby the enzyme from C. maxima. Application of 16-deoxo-DGC causedthe promotion of the growth of seedlings of both rice and cucumber. ³ Present address: Genetic Engineering Center, Korea Instituteof Science and Technology, Daejeon 305–606, Korea ⁴ Present address: Department of Agricultural Chemistry, UtsunomiyaUniversity, Utsunomiya-shi, Tochigi, 321 Japan (Received September 25, 1990; Accepted December 17, 1990)     

Metabolism of Gibberellins in Cell-Free Extracts of Anthers from Normal and Dwarf Rice

Cell-free extracts were prepared from anthers of normal anddwarf rice (Oryza sativa L.), and the metabolism of radioisotope-labeledgibberellins in the extracts was analyzed by HPLC and gas chromatography-massspectrometry (GC/MS). GA₁₂ was converted to GA₁₅ and GA₃₄ inthe extracts. GA₂₀ was converted to GA¹, GA₈ and GA₂₉, but GA₉was converted only to GA₃₄. The extracts of the dwarf cultivar,Waito-C (dy mutant), showed the same 3ß-hydroxylationactivity as did those of the normal cultivar, Nihonbare, indicatingthat the dy gene is not expressed in the anthers. These resultssuggest that the regulation of the biosynthesis of gibberellinsin rice is organ-specific. (Received November 9, 1989; Accepted January 10, 1990)     

Quantitative Analysis of Endogenous Gibberellins in Normal and Dwarf Cultivars of Rice

Endogenous levels of gibberellins in shoots and ears of twodwarf rice (Oryza sativa L.) cultivars, Tan-ginbozu (dx mutant)and Waito-C (dy mutant), were analyzed and compared with thoseof normal rice cultivar, Nihonbare. The endogenous levels of13-hydroxylated gibberellins in Tan-ginbozu were much lowerthan those in Nihonbare. In Waito-C, the levels of GA₁₉ andGA₂₀ in the shoots were higher but that of GA₁ was lower thanthe levels of these gibberellins in Nihonbare. These resultssupport the hypothesis that the dy gene controls the 3ß-hydroxylationof GA₂₀ to GA₁ while the dx gene controls a much earlier stepin the gibberellin biosynthesis. Our results indicate that GA₁is the active gibberellin that regulates the vegetative growthof rice. The endogenous levels of GA₄ in the ears of the twodwarf cultivars of rice were higher than the level of GA₄ inthe ears of the normal cultivar, Nihonbare suggesting that thebiosynthesis of gibberellin is not blocked in the anthers ofthe dwarf rice. (Received April 27, 1989; Accepted July 12, 1989)     

Effects of a New Plant Growth Regulator Prohexadione Calcium (BX-112) on Shoot Elongation Caused by Exogenously Applied Gibberellins in Rice (Oryza sativa L.) Seedlings

The effects of a novel plant growth regulator (PGR) prohexadionecalcium (BX-112; calcium 3,5-dioxo-4-propionylcyclohexanecarboxylate)on shoot elongation caused by exogenously applied GA₁, GA₃,GA₄₎ GA₁₉ and GA₂₀ were investigated in rice (Oryza sativa L.cv. Nihonbare and cv. Tan-ginbozu) seedling test. Dependingon the dose, BX-112 reduced shoot elongation in both cultivarscaused by GA₁₉ and GA₂₀, but not by GA₁. When a high dose ofBX-112 (e.g. 250 ng/plant and over) was applied with GA₁, orGA₄, shoot elongation was even promoted. This promotive effect,however, was not observed with GA₃. These results suggest thatBX-112 inhibits gibberellin (GA) biosynthesis in the rice plantat the 3ß- and 2ß-hydroxylation of GAs,namely steps of activation and inactivation, respectively. (Received September 6, 1989; Accepted November 27, 1989)     

Partial Purification and Characterization of Gibberellin 3{beta}-hydroxylase from Immature Seeds of Phaseolus vulgaris L.

Gibberellin 3/ß-hydroxylase,a 2-oxoglutarate-dependentdioxygenase that catalyzes the hydroxylation of GA₂₀ to GA₁,was purified 313-fold from immature seeds of Phaseolus vulgarisL. The mol wt of the enzyme was estimated to be 42,000 by gelfiltration HPLC and SDS-polyacrylamide gel electrophoresis.The enzyme exhibited maximum activity at pH 7.7. The Km valuesfor [2,3-³H]GA20 and [2,3-³H]GA, were 0.29µu and 0.33µm, respectively. The enzyme requires 2-oxoglutarate asa cosubstrate; the K_m value for 2-oxoglutarate was 250µMusing [³H]- GA₂₀ as a substrate. Fe²⁺ and ascorbate significantlyactivated the enzyme at all purification steps, while catalaseand BSA activated the purified enzyme only. The enzyme was inhibitedby divalent cations Mn²⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Cd²⁺ and Hg²⁺.3ß-Hydroxylation of [³H]- GA₂₀ was also inhibitedby non-radioactive GA₅, GA₉,GA₁₅, GA₂₀ and GA₄₄. The possiblesite of 3ß-hydroxylation in gibberellin biosynthesisis discussed in terms of the substrate specificity of partiallypurified gibberellin 3ß-hydroxylase. (Received February 29, 1988; Accepted June 3, 1988)     

Effects of Fluorogibberellins on Plant Growth and Gibberellin 3r{beta}-Hydroxylases

3rß-Fluorogibberellin A₉ (3rß-fluoro-GA₉),3rßfluoro-GA₂₀, 3rß-fluorodeoxygibberellinC (3rß-fluoro-DGC) and 13-fluoro-GA₉ were prepared,and their effects on plant growth and gibberellin (GA) 3rß-hydroxyIaseswere examined. 3rß-Fluoro-GA₉ and 3rß-fluoro-GA₂₀promoted the growth of dwarf rice (Oryza sativa L. cv. Tan-ginbozu)seedlings to three times higher than the control seedlings ata dosage of 3 µ plant^–1, and 3rßfluoro-DGCto twice higher at the same dosage. 3rßg-Fluoro-GA₉was active in cucumber (Cucumis sativus L.) hypocotyl assay,its activity being about one-thirtieth as much as that of GA₄.3rß-Fluoro-GAs were active per se in promoting theshoot elongation of rice. 3rß-Fluoro-DGC inhibitedthe 3rß-hydroxylation of [³H₂]GA₉ to [³H]GA₄ by GArß-hydroxylase from bean (Phaseolus vulgaris L.),but 3rß-fluoro-GA₉ and 3rß-fluoro-GA₂₀ didnot show any effects on the enzyme activity. These 3rß-fluoro-GAsalso showed no or only a weak inhibitory effect on the rß-hydroxylasefrom pumpkin (Cucurbita maxima L.). 13-Fluoro-GA₉ promoted growthof rice and cucumber seedlings, and inhibited the 3rß-hydroxylasesfrom both bean and cucumber. 13-Fluoro-GA₉was converted into13-fluoro-GA₄ and 2,3-didehydro-13-fluoro-GA₉, in a cell-freesystem from bean, and conversion of 13-fluoro-GA₉ into 13-fluoro-GA₄was also observed in a cell-free system from pumpkin. Theseresults suggest that 13-fluoro-GA₉ is one of the substratesof GA 3rß-hydroxy-lases, and that 13-fluoro-GA₉ isactive as a result of the conversion to 13-fluoro-GA₄ in riceand cucumber seedlings. (Received October 27, 1997; Accepted March 13, 1998)     

Internode Length in Pisum. A New Allele at the le Locus

In Pisum sativum L. a third, more severe, allele at the internodelength locus le is identified and named le^d. Plants homozygousfor le^d possess shorter internodes and appear relatively lessresponsive to GA₂₀ than comparable le (dwarf) plants. Gene le^dmay act by reducing the 3ß-hydroxylation of GA₂₀ tothe highly active GA₁ more effectively than does gene le. Theresults indicate that le is a leaky mutant and therefore thatendogenous GA₁ influences internode elongation in dwarf (le)plants. Pisum sativum, peas, internode length, genetics, gibberellin, dwarf elongation     

Effects of Gibberellins and Prohexadione on the Activities of Oryzain and {alpha}-Amylase in Rice Seeds

Oryzains, cysteine proteinases of rice seeds, are induced byGA₃ in germinating rice seeds [Abe et al. (1987) Agric. Biol.Chem. 51: 1509]. The effects of GA₁, GA₃, GA₄, GA₉, and GA₂₀on the production of oryzain and -amylase were investigatedin embryoless half- and whole-seeds of rice (cv. Nipponbare).When gibberellins (GAs) were incubated with embryoless half-seeds,GA₁, GA₃ and GA₄ induced oryzain and -amylase, but GA₉, andGA₂₀ did not. GA₉ and GAM induced oryzain and -amylase productionin whole seeds, but this production was inhibited by the simultaneousapplication of prohexadione, an inhibitor of 2ß- and3ß-hydroxylation of GAs. Prohexadione did not inhibitthe activities of oryzain and -amylase induced by GA₁. Theseresults suggest that GAs possessing the 3ß-hydroxylgroup induce activities of oryzain and -amylase in rice seedsand that GA₉ and GA₂₀ have activity only after they are convertedmetabolically to active GAs, probably GA₄ and GA₁, respectively.GA₁, was more active than GA₄ in both half seeds and wholeseeds incubation. Oryzain and -amylase activities induced byGA₄ were significantly inhibited in the presence of 10^–4M prohexadione. This suggests that the conversion of GA₁, toGA₄ (13-hydroxylation) might be inhibited at a high dose ofprohexadione in whole seeds. ⁴Present address: Institute of Food Development, Kyung Hee University,Suwon 449-701, Korea     

Interaction of naphthol with EDDHA/salicylic acid in flowering and gibbosity of Lemna gibba G3

Flowering and gibbosity in Lemna gibba G3, as enhanced or inducedby optimal concentrations of salicylic acid or EDDHA, was specificallyinhibited by 10 µg/ml and higher concentrations of ß-naphthol.These effects of ß-naphthol are similar to those ofbreakdown products of GA_s. (Received March 20, 1978; )     

Effects of a Plant Growth Regulator, Prohexadione Calcium (BX-112), on the Elongation of Rice Shoots Caused by Exogenously Applied Gibberellins and Helminthosporol, Part II

Prohexadione calcium (BX-112) is a novel plant growth regulatorthat inhibits the late stages of the biosynthesis of gibberellinsin plants. Fourteen kinds of gjbberellin, helminthosporol and'helminthosporic acid were applied simultaneously with BX-112to rice seedlings (Oryza sativa L. ), and their growth-promotingactivities in terms of shoot elongation were examined. The growth-promotingactivities of GA₁, GA₄, GA₁₈, GA₂₂, GA₂₃, GA₃₈, helminthosporoland helminthosporic acid were not inhibited by BX-112, but thoseof GA₅, GA₉, GA₁₅, GA₁₉, GA₂₀, GA₃₁, GA₄₄ and GA₅₃ were inhibited.These results suggest that 3ß-hydroxylation is animportant and necessary step in the biosynthesis of gibberellinsthat promote shoot elongation in rice seedlings. The weak promotionof shoot elongation by GA₂₂ in the presence of BX-112 suggeststhat the effect of a hydroxyl group at C-18 of GA₂₂ might beable to mimic the effect of the 3ß-hydroxyl groupof GA₁. Helminthosporol and helminthosporic acid may promotethe shoot elongation of rice by mimicking physiologically activegibberellins and not by stimulating their biosynthesis. ¹Part I is the previous paper by Nakayama et al. (1990a) ³Present address: Frontier Research Program RIKEN, Wako-shi,Saitama, 351-01 Japan. (Received June 26, 1991; Accepted September 4, 1991)     

Identification and Semi-Quantification of Gibberellins from the Pollen and Anthers of Zea mays by Immunoassay and GC/MS

Radioimmunoassays and enzyme-linked immunosorbent assays formethyl esters of gibberellins A₁, A₃, A₄, and A₇ were establishedusing an antiserum specific for GA₁-Me. The antiserum was characterizedby high titer and specificity for such C₁₉-GAs with 3ß-hydroxylgroup as GA₁, GA₃, GA₄ and GA₇. Combination of this antiserumand HPLC enabled us to identify and quantify GA, and GA₄ fromthe pollen of Zea mays with a high degree of reliability. Similarly,identification and quantification of GA₉ and GA₂₀ were alsomade possible by use of an antiserum specific for GA₂₀-Me. Combineduse of immunoassays and GC/MS enabled us to identify nine GAsfrom the pollen and four from the anthers of Zea mays. The identificationof non-13-hydroxylated GAs, such as GA₄ and GA₉, in additionto 13-hydroxylated GAs from the pollen and the anthers suggeststhat the early-non-hydroxylation pathway, as well as the early-13-hydrox-ylationpathway, operates in the male reproductive organs of Zea mays,and that the organ-specific biosynthesis and/or localizationof GAs in Zea mays is similar to that in Oryza saliva. (Received May 7, 1990; Accepted August 20, 1990)     

Levels of {beta}-Glucan and Lignin in Elongating Internodes of Deepwater Rice

Partial submergence or treatment with either ethylene or gibberellicacid (GA₃ induces rapid growth in deepwater rice (Oryza sativaL.). We correlated the synthesis of two cell wall componentswith two phases of internodal elongation, namely (13,14)-ß-glucanformation with cell elongation and lignification with differentiationof the secondary cell wall and cessation of growth. The contentof ß-glucan was highest in the zone of cell elongationin internodes of air-grown plants and plants that were inducedto grow rapidly by submergence. In the intercalary meristemand in the differentiation zone of the internode, ß-glucanlevels were ca. 70% lower than in the zone of cell elongation.The outer cell layers, enriched in epidermis, contained moreß-glucan in submerged, rapidly growing internodesthan in air-grown, control internodes. The ß-glucancontent of the inner, parenchymal tissue was unaffected or slightlylowered by submergence. The epidermis appears to be the growth-limitingstructure of rapidly growing rice internodes. We hypothesizethat elevated levels of ß-glucan contribute to elongationgrowth by increasing the extensibility of the cell wall. Lignificationwas monitored by measuring the content of lignin and the activitiesof two enzymes of the lignin biosynthetic pathway, coniferylalcohol dehydrogenase (CAD) and phenylalanine ammonia-lyase(PAL), in growing and non-growing regions of the internode.Using submerged whole plants and GA₃-treated excised stem segments,we showed that lignin content and CAD activity were up to sixfoldlower in newly formed internodal tissue of rapidly growing ricethan in slowly growing tissue. No differences were observedin parts of the internode that had been formed prior to inductionof growth. PAL activity was reduced throughout the internodeof submerged plants. We conclude that lignification is one ofthe processes that is suppressed to permit rapid growth. ¹ This work was supported by the National Science Foundationthrough grants No. DCB-8718873 and DCB-9103747 and by the Departmentof Energy through grant No. DE-FGO2-90ER20021. M.S. was therecipient of a fellowship from the Max Kade Foundation.     

Flexibility in the donor substrate specificity of {beta} 1,4-galactosyltransferase: application in the synthesis of complex carbohydrates

Biosynthetically, bovine N-acetylglucosainine ß 1,4-galacto-syltransferase(GalT) catalyses the transfer of galactosyl residues from UDP-Galto the 4-position of GlcNAc units, resulting in the productionof N-acetyllactosamine sequences. UDP-Glc and UDP-GalNAc werealso found to act as donors for this enzyme, allowing the preparationof ßGlc(14)-ßGlcNAc and ßGalNAc(14)ßGlcNActerminating structures on the milligram scale. GalT could thusbe used to add ßGalNAc to ßGlcNAc(12)Manterminating structures, converting them to the ßGalNAc(14)ßGlcNAc(12)Mansequences found on glycoprotein hormones. GalT did not transferGlcNAc residues from UDP-GlcNAc, but it could utilize UDP-GlcNH₂as a donor. Synthesis of ßGlcNAc(14)ßGlcNAcsequences could therefore be accomplished by transfer of GlcNH₂from its UDP derivative, followed by N-acetylation of the productamino-disaccharide using acetic anhydride in methanol. The productsof the enzymatic reactions were characterized by ¹H-NMR-spectroscopyand fast-atom bombardment mass spectrometry. This work expandsthe scope of the combined chemical-enzymatic synthesis of complexcarbohydrates, using glycosyltrans-ferases, to the productionof oligosaccharides different from those for which these enzymeswere designed. These unnatural reactions should find applicationin glycoprotein and glycolipid remodelling. galactosyltransferase chemica1-enzymatic synthesis of oligosaccharides oligosaccharide analogues sugar-nucleotide analogues carbohydrate remodelling     

Identification and Quantification of Cambial Region Hormones of Eucalyptus globulus

Gibberellins GA₁, GA₄, GA₈, GA₉, GA₁₉, GA₂₀, GA₂₉, GA₄₄, GA₈₁,indole-3-acetic acid (IAA) and abscisic acid (ABA) were identifiedin cambial region tissues of Eucalyptus globulus by comparingmass spectra and Kovats retention indices with those of authenticstandards. Using stable isotope labelled internal standardsGA₁₉, GA₂₀ and GA₄₄ were quantified at levels of 2–7 ng(g fr wt)^-1, other GAs were present at levels < 1 ng (g frwt)^-1. Levels of IAA and ABA ranged from 417–1, 140 ng(g fr wt)^-1 and 86–305 ng (g fr wt)^-1 respectively. Thepresence of brassinosteroid-like substances was also indicatedbased on activity in the rice seedling leaf inclination assay. (Received April 28, 1995; Accepted June 20, 1995)     

Zinc Deficiency Affects the Levels of Endogenous Gibberellins in Zea mays L.

Zinc deficiency in Zea mays L. markedly reduced the level ofGA₁, but not GA₂₀, suggesting blockage of 3rß-hy-droxylation.The level of IAA was also decreased although not as markedly.Castasterone was affected less than IAA by zinc deficiency. (Received February 24, 1997; Accepted June 24, 1997)     

Metabolism of [14C]GA20 in a Cell-Free System from Developing Seeds of Phaseolus vulgaris L.

The metabolism of [¹⁴C]GA₂₀ during seed maturation of Phaseolusvulgaris was studied using cell-free systems from embryos rangingin age from 10 DAF (day after flowering) to 24 DAF. Enzyme preparationsfrom very immature seeds actively converted GA₂₀ to GA¹, GA₅and GA₆. The ratio of incubation products suggested the biosyntheticpathway of GA₂₀—GA₅—GA₆. Fluctuation in the levelsof endogenous C₁₉-GAs, namely GA₁, GA₄, GA₅, GA₆, GA₈, GA₉ andGA₂₀ was analyzed by GC-SIM using internal standards to compareenzyme activity with the levels of endogenous GAs. AlthoughGA₁, GA₄ and GA₆ showed maximum levels on 20 DAF, enzyme activitydecreased during seed maturation and showed weak activity on20 DAF. ¹Graduate student of the University of Tokyo, Department ofAgricultural Chemistry, Bunkyo-ku, Tokyo 113, Japan. ³Present address: Pesticides Research Laboratory, TakarazukaResearch Center, Sumitomo Chemical Co., Ltd., Takarazuka, Hyogo655, Japan. (Received December 17, 1987; Accepted March 30, 1988)