Bruce Twitchin

Synthesis of gibberellin GA6 and its role in flowering of Lolium temulentum.

The induction of flowering by one long day (LD) in the grass Lolium temulentum is most closely mimicked by application of the gibberellins (GAs) GA(5) or GA(6), both of which occur naturally. These gibberellins promote floral development but have little effect on stem elongation. Endogenous GA(5) and GA(6) contents in the shoot apex double on the day after the LD and, for GA(5) (and we presume for GA(6) as well) reach a concentration known to be inductive for the excised shoot apex in vitro. They are, therefore, strong candidates as LD floral stimuli in this grass. The synthesis of GA(6) and an examination of its florigenic properties in L. temulentum are described.

Changes in free and conjugated indole-3-acetic acid during early stage of flower bud differentiation in Polianthes tuberosa

Tuberose (Polianthes tuberosa L. cv. Double) corms at the vegetative, early floral initiation, and flower bud differentiation stages were assayed for free indole-3-acetic acid (IAA), esterified IAA, and peptidyl IAA. The corms in the vegetative stage contained higher free IAA than those from the early floral initiation stage. Free IAA in corm tissues increased 2.7-fold at flower bud differentiation as compared to the vegetative stage. In the vegetative corms, a marked promotion of leaf differentiation was recorded. In contrast, corms from the early floral initiation stage contained less free IAA, whereas esterified IAA and peptidyl IAA increased dramatically. It is concluded that the level of free IAA in vegetative corms is correlated with leaf differentiation, and that the early floral initiation stage is correlated with a reduction in free IAA and an increase in IAA conjugates in the corms. Moreover, increases in free IAA and decreases in IAA conjugates in the floral differentiation stage, as compared to the early floral initiation stage, indicates that free IAA is correlated with flower development.

Endogenous gibberellins in immature seeds of Prunus persica L.: identification of GA118, GA119, GA120, GA121, GA122 and GA126

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.

Preparation of tert-butyldimethylsilyl (tbdms) enol ethers using potassium hydride in the presence of tbdms chloride

Abstract TBDMS enol ethers can be readily prepared regio- and stereoselectively under equilibrating conditions in high yield by adding potassium hydride to a THF solution of ketone with TBDMS chloride in situ .

Gibberellins in immature seed of Prunus cerasus: Structure determination and synthesis of gibberellin, GA95 (1,2-Didehydro-GA20)

Abstract Ten C-13-hydroxylated gibberellins (GA 3 , GA 17 , GA 19 , GA 20 , GA 32 , GA 44 , GA 86 , GA 87 , GA 95 and GA 95 isolactone) and two C-13-deoxy-GAs (GA 25 and GA 30 ) were identified in immature seeds of sour cherry ( Prunus cerasus L. cv. Montmorency) by GC-mass spectrometry. GA 95 is a new GA whose structure was determined to be 1,2-didehydroGA 20 by GC-mass spectral comparison with an authentic sample, synthesized from GA 3 . In addition, six unknown GA-like compounds were detected by GC-mass spectrometry. It remains unclear whether GA 95 isolactone was an artefact. On the basis of the structures of the endogenous GAs and the absence of GA 5 , the sequence of GA 20 → GA 95 → GA 3 → GA 87 → GA 32 could be conceived of as a possible biosynthetic pathway.

Effects of 17-alkyl-16,17-dihydrogibberellin A5 derivatives on growth and flowering in Lolium temulentum

Several gibberellins in which the 16-methyl group of the 16-epimers of dihydro-GA(5) had been replaced by ethyl, n-propyl and n-butyl were prepared and tested at doses of 1, 5 or 25&mgr;g per plant for their effects on stem growth and flowering of the grass Lolium temulentum. The ethyl and n-propyl derivatives were most inhibitory of elongation, the exo-isomers being more active than the endo-forms. While both isomers of dihydro-GA(5) promoted flowering, among the 17-alkyl analogues, only the exo-ethyl derivative showed significant activity.

Methodology for translocating the carboxy group in gibberellins: the partial synthesis of 7(6→15βH)abeo-GA4

Abstract The carboxylic acid group has been excised from phytohormone gibberellin A4 and relocated on the D-ring, thereby generating a new clas of gibberellin derivatives related structurally to helminthosporic acid.

3β,13-Dihydroxylated C20 gibberellins from inflorescences of Rumex acetosa L.

Abstract Using full scan GC–MS a wide range of gibberellins (GAs) was identified in the young inflorescences of the dioecious species Rumex acetosa L., consistent with the ubiquitous early 13-hydroxylation pathway in both male and female plants. In addition, R. acetosa is the first species in which all three 3β,13-dihydroxylated C 20 -GAs—GA 18 , GA 38 and GA 23 —have been identified in the same organism, suggesting an early 3β,13-dihydroxylation biosynthesis pathway in this species. Authentic GA 18 , GA 38 and GA 23 were synthesized and their effects and that of GA 1 , a GA common to both pathways, on the time to inflorescence emergence was investigated. GA 1 accelerated the emergence of inflorescences in both male and female plants. In addition some evidence for biological activity per se of the C 20 -GA 38 was obtained.

Synthesis of GA73 methyl ester, a potent gibberellin-derived antheridiogen from gametophytes of the fern lygodium japonicum

Abstract Iodolactonisation of gibberellin Δ 9 -ene-19-oic acids followed by DBU induced dehydrohalogenation provides good access to gibberellin Δ 9(11) -enes, including the potent antheridiogen, Δ 9(11) -didehydroGA 9 methyl ester ( 1 ), isolated from gametophytes of the fern Lygodium japonicum .