Extracts of mature wheat grain have been analysed by GC–MS and found to contain two new metabolites. The syntheses of the two new gibberellins, 1β-hydroxy-2β,3β-epoxyGA9 4 and 1β-hydroxy-2β,3β-epoxyGA20 5 from the fungal gibberellins, GA7 and GA3 are described. A range of protecting groups for the 7-carboxylic acid which can be removed under mild conditions, are compared. The allyl ester proved most valuable in the manipulation of these multifunctional molecules and it is removed with tetrakis(triphenylphosphine)palladium(0), triphenylphosphine and potassium isobutyrate. The structures of the new natural products in wheat were confirmed to be 4 and 5 by comparison with the GC–MS data from the synthetic samples and are assigned the trivial names GA94 and GA93 respectively.
Because of the breeding value of gibberellic acid (GA3) insensitive semidwarf genotypes in wheat, a screening for GA3 response within a collection of semidwarf ryes was initiated and up to now four genotypes ('Moskowskij Karlik', 'Gülzow kurz', 'R18', 'Dwarf C) were found to be insensitive to applied gibberellic acid. In contrast to wheat, where all of the known alleles for GA insensitivity are (partially) dominant, the genetical studies did show that these four genotypes are carrying recessive alleles. Furthermore, it was found that the alleles of 'Moskowskij Karlik' and 'R18 seem to have the same locus on chromosome 5R, whereas the GA insensitivity of 'Gülzow kurz' and 'Dwarf C' is governed by two alleles of a different locus on chromosome 7R. None of the identified alleles was located on chromosome 4R, which could have been expected from the homoeologous relationships to wheat chromosomes 4B and 4D, which are critical for GA insensitivity. Studies on endogenous levels of gibberellins are in accordance with the genetical results, and suggest the GA insensitivity in rye to be caused by a different mechanism, compared to wheat.
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Embryo and caryopsis dormancy, abscisic acid (ABA) responsiveness, after-ripening (AR), and the disorder pre-harvest sprouting (PHS) were investigated in six genetically related wheat varieties previously characterized as resistant, intermediate, or susceptible to PHS. Timing of caryopsis AR differed between varieties; AR occurred before harvest ripeness in the most PHS-susceptible, whereas AR was slowest in the most PHS-resistant. Whole caryopses of all varieties showed little ABA-responsiveness during AR; PHS-susceptible varieties were responsive at the beginning of the AR period whereas PHS-resistant showed some responsiveness throughout. Isolated embryos showed relatively little dormancy during grain-filling and most varieties exhibited a window of decreased ABA-responsiveness around the period of maximum dry matter accumulation (physiological maturity). Susceptibility to PHS was assessed by overhead misting of either isolated ears or whole plants during AR; varieties were clearly distinguished using both methods. These analyses allowed an investigation of the interactions between the different components of seed development, compartments, and environment for the six varieties. There was no direct relationship between speed of caryopsis AR and embryo dormancy or ABA-responsiveness during seed maturation. However, the velocity of AR of a variety was closely associated with the degree of susceptibility to PHS during AR suggesting that these characters are developmentally linked. Investigation of genetic components of AR may therefore aid breeding approaches to reduce susceptibility to PHS.
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