Abscisic-acid-deficient mutants at the aba gene locus of Arabidopsis thaliana are impaired in the epoxidation of zeaxanthin

Abstract. The xanthophyll content of wild type and abscisic acid (ABA) - deficient mutants of pea and Arabidopsis thaliana was determined. The wilty mutant of pea was indistinguishable from the non-mutant control. In contrast, plants homozygous for mutant alleles at the aba locus of Arabidopsis were very different from wild type. In these mutants, zeaxanthin accumulated to abnormally high levels. The major carotenoids, violaxanthin and 9'- cis -neoxanthin were virually absent from the mutant chromatograms. It was concluded that the aba genetic lesion impairs the epoxidation of zeaxanthin to violaxanthin and that this results in an inability to accumulate ABA. This provides clear evidence that zeaxanthin is a precursor of ABA.     

Volatile chemical release by bethylid wasps: identity, phylogeny, anatomy and behaviour

The structures of volatile chemicals released by parasitic wasps in the family Bethylidae are shown to correspond to the subfamily to which the species belong. Species in the Epyrinae release skatole (3-methylindole) and species in the Bethylinae release a spiroacetal (2-methyl-1,7-dioxaspiro [5.5]undecane): these compounds are chemically very different. The enantiomeric composition of the spiroacetal differs between congeneric species. Chemical release is a discrete event under the active control of both male and female wasps. Structural differences between the mandibular glands and intramandibular glands suggest the mandibular glands to be the source of released volatiles. Real-time mass spectrometry shows that the spiroacetal is released by Goniozus nephantidis females during dyadic resource contests, with release more common during more aggressive interactions. Chemical tagging with deuterium further shows that the volatile is released by the loser of an agonistic interaction and not the winner. The function of spiroacetal and skatole release by bethylids is discussed.  © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 94 , 837–852.     

The wilty tomato mutants flacca and sitiens are impaired in the oxidation of ABA-aldehyde to ABA

Abstract. Deuterium-labelled ABA-aldehyde was fed to various tomato genotypes. Normal and notabilis mutant plants incorporated substantial amounts of the label into ABA. In contrast, two ABA-deficient mutants, flacca and sitiens , reduced ABA-aldehyde to a mixture of cis- and trans -ABA alcohol rather than oxidizing it to ABA. It was concluded that ABA-aldehyde is the immediate precursor of ABA in higher plants. It appears that the flacca and sitiens lesions both act to block the last step of the ABA biosynthetic pathway. The mutant gene loci are likely to be involved in coding for different sub-units of the same dehydrogenase enzyme.     

Abscisic Acid and C10 Dicarboxylic Acids in Wilty Tomato Mutants

Linforth, R. S. T., Taylor, I. B. and Hedden, P. 1987. Abscisicacid and C10 dicarboxylic acids in wilty tomato mutants.—J.exp. Bot. 38: 1734–1740. The concentration of C₁₀ dicarboxylic acids in wilty tomatomutants was investigated. Three of the genotypes studied (flacca,sitiens and the double mutant homozygote flacca/sitiens) werefound to have higher concentrations of 2,7-dimethyl-2,4-octadienedioicacid (ODA) than the isogenic normal form. In contrast, the othergenotypes (notabilisand the double mutant homozygotes notabilis/flaccaand notabilis/sitiens) were found to have lower concentrationsof ODA than the isogenic normal form. The concentration of ODAin flacca plants was increased by water stress and reduced byexogenously applied abscisic acid (ABA). A second structurallyrelated compound, 2,7-dimethyl-4-octenedioic acid (OEA) wasalso quantified, but it showed no clear genotype-related pattern. The concentration of ABA in the wilty tomato mutants was alsoinvestigated. As expected in the light of previously publishedresults, it was reduced in the single mutants relative to theisogenic control plants. In the double mutant flacca/sitiensABA levels were similar to those of the single mutant sitiens.However, in the two double mutants notabilis/flacca and notabilis/sitiensABA was substantially lower than those in any other genotypeinvestigated. Key words: Abscisic acid, 2,7-dimethyl-2,4-octadienedioic acid, 2,7-dimethyl-4-octenedioc acid, tomato, wilty mutants     

The Metabolism of cis ABA-aldehyde by the Wilty Mutants of Potato, Pea and Arabidopsis thaliana

RS-[²H₁] cis ABA-aldehyde was fed to ABA-deficient mutants ofpotato (droopy), pea (wilty) and Arabidopsis thaliana (aba¹)along with appropriate non-mutant controls. Both the wilty andaba¹ mutants readily oxidized the monodeuterated ABA-aldehydeto ABA. The incorporation of label into ABA by these two mutantswas indistinguishable from that detected in the non-mutant controls.In contrast, the droopy mutants poorly incorporated the labelledprecursor into ABA. Instead they reduced and isomerized RS-[²H₁] cis ABA-aldehyde to a mixture of 2, cis and 2, trans ABA-alcohols.Thus the droopy mutant affects the last step in ABA biosynthesis,a position it shares with the tomato mutants, flacca and sitiens.Genetic evidence suggesting that droopy and sitiens may be correspondinggene loci is discussed. Key words: ABA metabolism, wilty mutants, pea, potato, Arabidopsis     

2-trans-ABA alcohol accumulation in the wilty tomato mutants flacca and sitiens

Abstract Two wilty tomato mutants, flacca and sitiens, fail to increase their endogenous ABA concentration in response to water stress. Instead, a compound accumulates which has been identified as 2-trans-ABA alcohol. Levels of this compound have been estimated for three wilty mutants and the control; both before and after water stress. When the compound was biosynthesized in the presence of ¹⁸O₂, one atom appeared to be incorporated into the primary alcohol group. The possible implications of this for the ABA biosynthetic pathway are discussed.