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  • 1
    Electronic Resource
    Electronic Resource
    Carotenoids and abscisic acid (ABA) biosynthesis in higher plants (1991)
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 82 (1991), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Recent research has revealed that abscisic acid (ABA), synthesised in response to water stress, is an apo-carotenoid. Two potential carotenoid precursors, 9′-cis-neoxanthin and 9-cis-violaxanthin, have been identified in light-grown and etiolated leaves, and in roots of a variety of species. Experiments utilizing etiolated Phaseolus vulgaris leaves and deuterium oxide strongly suggest that 9′-cis-neoxanthin, synthesised from all-trans-violaxanthin, is the immediate pre-cleavage precursor of ABA. The cleavage of 9′-cis-neoxanthin, performed by an inducible and specific dioxygenase, is likely to be the rate-limiting step in ABA biosynthesis. Any apocarotenoids formed as by-products of cleavage are probably rapidly degraded by lipoxygenase or related enzymes. After cleavage xanthoxin is converted via ABA-aldehyde to ABA by constitutive enzymes in the cytosol.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1399-3054.1991.tb00100.x
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  • 2
    Electronic Resource
    Electronic Resource
    Jasmonic acid and abscisic acid in shoots, coleoptiles, and roots of wheat seedlings (1994)
    Springer
    Journal of plant growth regulation 13 (1994), S. 59-62 
    Details
    ISSN: 1435-8107
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The endogenous levels of abscisic acid (ABA) and jasmonic acid (JA) were analyzed in wheat seedlings grown in water, a system which in the past has been used to test the effects of these plant growth inhibitors. The levels in different plant parts and in the medium were measured by gas chromatography-mass spectrometry-selected ion monitoring, using [2H3]ABA and [2H6]JA as internal standards. In every plant part, JA levels were about 2 orders of magnitude greater than those of ABA. The exudation of JA from roots per seedling was about 14,000-fold greater than that of ABA, although the roots contained only about 170 times more JA than ABA. It is suggested that JA is a possible allelopathic compound.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00210947
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  • 3
    Electronic Resource
    Electronic Resource
    Mass-spectrometric quantitation of cytokinins in tobacco crown-gall tumours induced by mutated octopine Ti plasmids of Agrobacterium tumefaciens (1988)
    Springer
    Planta 176 (1988), S. 230-234 
    Details
    ISSN: 1432-2048
    Keywords: Agrobacterium ; Auxin in tumors ; Cytokinin (in tumors, turnover, oxidase) ; Mutant (T-DNA) ; Nicotiana (crown gall) ; T-DNA mutants
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The levels of the major cytokinins, zeatin, zeatin riboside, zeatin riboside-5′-monophosphate and zeatin-7-glucoside were measured in tobacco (Nicotiana tabacum L.) crown-gall tissues carrying insertion and deletion mutations in the T-DNA. Measurements were made by combined gas chromatography-mass spectrometry using selected ion monitoring with 15N- and 2H-labelled internal standards. The results demonstrate that, relative to wild-type tumour tissue, cytokinin levels are considerably elevated in tissues lacking functional T-DNA auxin-biosynthetic genes. From a detailed analysis of the major cytokinin metabolites it is concluded that a reduction in the extent of cytokinin degradation via N6-side-chain cleavage is an important factor leading to increased cytokinin levels in these tissues.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00392449
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  • 4
    Electronic Resource
    Electronic Resource
    Abscisic acid biosynthesis in roots (1992)
    Springer
    Planta 187 (1992), S. 185-191 
    Details
    ISSN: 1432-2048
    Keywords: Abscisic acid biosynthesis (precursors) ; Carotenoid ; Lycopersicon (ABA biosynthesis) ; Neoxanthin (isomers) ; Root (abscisic acid) ; Violaxanthin(isomers)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The pathway of water-stress-induced abscisic acid (ABA) biosynthesis in etiolated and light-grown leaves has been elucidated (see A.D. Parry and R. Horgan, 1991, Physiol. Plant. 82, 320–326). Roots also have the ability to synthesise ABA in response to stress and it was therefore of interest to examine root extracts for the presence of carotenoids, including those known to be ABA precursors in leaves. All-trans- and 9′-cis-neoxanthin, all-trans- and 9-cis-violaxanthin, antheraxanthin (all potential ABA precursors), lutein and β-carotene were identified on the basis of absorbance spectra, reactions with dilute acid, retention times upon high-performance liquid chromatography and by comparison with leaf carotenoids that had been analysed by mass spectrometry. The source of the extracted carotenoids was proved to be root tissue, and not contaminating compost or leaf material. The levels of total carotenoids in roots varied between 0.03–0.07% of the levels in light-grown leaves (Arabidopsis thaliana (L.) Heynh, Nicotiana plumbaginifolia Viv., Phaseolus vulgaris L. and Pisum sativum L.) up to 0.27% (Lycopersicon esculentum Mill.). The relative carotenoid composition was very different from that found in leaves, and varied much more between species. All-trans-neoxanthin and violaxanthin were the major carotenoids present (64–91 % of the total), but while Lycopersicon contained 67–80% all trans-neoxanthin, Phaseolus, Pisum and Zea mays L. contained 61–79% all-trans-violaxanthin. Carotenoid metabolism also varied between species, with most of the carotenoids in older roots of Phaseolus being esterified. Roots and leaves of the ABA-deficient aba mutant of Arabidopsis had reduced epoxy-xanthophyll levels compared to the wild-type.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00201936
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  • 5
    Electronic Resource
    Electronic Resource
    Abscisic acid biosynthesis in roots (1992)
    Springer
    Planta 187 (1992), S. 192-197 
    Details
    ISSN: 1432-2048
    Keywords: Abscisic acid biosynthesis ; Carotenoid ; Lycopersicon (mutant) ; Mutant (ABA-deficient) ; Root (abscisic acid) ; Water stress
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The ubiquity of the apo-carotenoid abscisic acid (ABA) biosynthetic pathway elucidated in water-stressed, etiolated leaves of Phaseolus vulgaris (see A.D. Parry and R. Horgan, 1991, Physiol. Plant. 82, 320–326), has been difficult to establish. Light-grown leaves contain very high carotenoid: ABA ratios, preventing correlative studies, and no etiolated leaves so far studied, other than those of Phaseolus, have been found capable of synthesising significant amounts of ABA in response to stress. Roots are known to synthesise ABA and contain low carotenoid levels; therefore ABA biosynthesis was investigated in soil- and hydroponically grown roots of Lycopersicon esculentum Mill. Hydroponically grown roots were stressed by immersion in 100 mM mannitol and soil-grown roots by withholding water. In both cases stress led to an increase in ABA levels and a decrease in the levels of specific xanthophylls, namely all-trans- and 9′-cis-neoxanthin and all-trans-violaxanthin. In hydroponically grown roots, and soil-grown roots stressed after removal of the shoot, ratios of xanthophyll cleaved:ABA synthesised of approx. 1∶1 were obtained. These findings are consistent with the operation of an apo-carotenoid pathway in roots, involving the conversion of all-trans-violaxanthin via all-trans-neoxanthin, to 9′-cis-neoxanthin, and the specific cleavage of 9′-cis-neoxanthin to yield the C15 ABA precursor xanthosin. Similar experiments with roots of the “leaky”, ABA-deficient mutant of Lycopersicon, notabilis, indicate that the mutation does not affect the perception or transduction of stress, or the ability of the plant to cleave carotenoids. Rather, it appears that notabilis possesses an enzyme with reduced substrate specificity which cleaves more all-trans-than 9′-cis-neoxanthin.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00201937
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  • 6
    Electronic Resource
    Electronic Resource
    Abscisic-acid metabolism in a wilty mutant of Nicotiana plumbaginifolia (1991)
    Springer
    Planta 183 (1991), S. 237-243 
    Details
    ISSN: 1432-2048
    Keywords: Abscisic acid biosynthesis ; Mutant (wilty, abscisic-acid) ; Nicotiana (wilty mutant) ; trans-Abscisic acid-alcohol ; Xanthoxin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A mutant of Nicotiana plumbaginifolia, CKR1, isolated on the basis of its enhanced resistance to cytokinins was found to have a greater tendency to wilt than the wild type (Blonstein et al., 1991, Planta 183, 244–250). Further characterisation has shown that the wiltiness in the mutant is not caused by an insensitivity to abscisic acid (ABA) because the external application of ABA leads to stomatal closure and phenotypic reversion. The basal ABA level in the mutant is 〈 20% of that in the wild type. Following stress, the ABA level in wild-type leaves increases by approx 9-to 10-fold while the mutant shows only a slight increase. This deficiency in ABA is unlikely to be the consequence of accelerated catabolism as the levels of two major metabolites of ABA, phaseic and dihydrophaseic acid, are also much reduced in the mutant. The qualitative and quantitative distributions of carotenoids, the presumed presursors of ABA, are the same for the leaves of both wild type and mutant. Biosynthesis of ABA at the C15 level was investigated by feeding xanthoxin (Xan) to detached leaves. Wild-type leaves convert between 9–19% of applied Xan to ABA while the mutant converts less than 1%. The basal level of trans-ABA-alcohol (t-ABA-alc) is 3-to 10-fold greater in the mutant and increases by a further 2.5-to 6.0-fold after stress. This indicates that the lesion in the wilty mutant of N. plumbaginifolia affects the conversion of ABA-aldehyde to ABA, as in the flacca and sitiens mutants of tomato and the droopy mutant of potato (Taylor et al., 1988, Plant Cell Environ. 11, 739–745; Duckham et al., 1989, J. Exp. Bot. 217, 901–905). Wild-type tomato and N. plumbaginifolia leaves can convert trans-Xan into t-ABA-alc, and Xan into ABA, while those of flacca and the wilty N. plumbaginifolia mutant convert both Xan and t-Xan to t-ABA-alc.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00197794
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  • 7
    Electronic Resource
    Electronic Resource
    A cytokinin-resistant mutant of Nicotiana plumbaginifolia is wilty (1991)
    Springer
    Planta 183 (1991), S. 244-250 
    Details
    ISSN: 1432-2048
    Keywords: Abscisic acid biosynthesis ; Cytokinin resistance ; Mutant (wilty tobacco) ; Nicotiana (wilty mutant)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Selection for cytokinin resistance by incubating M2 seed of Nicotiana plumbaginifolia, after ethylmethanesulphonate mutagenesis, on 20 μM 6-benzylami-nopurine resulted in the isolation of a monogenic, recessive mutant, CKR1. Germination of the mutant is less sensitive to cytokinin inhibition than the wild type, and leaf development of the mutant occurs at cytokinin concentrations inhibitory to the wild type. Germination of the mutant is also resistant to auxin but not to abscisic acid. Three other traits jointly inherited with cytokinin resistance in the F2 are lack of root branching, precocious germination and wiltiness. The wilty phenotype is the consequence of the failure of stomatal closure during water stress.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00197795
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  • 8
    Electronic Resource
    Electronic Resource
    Cytokinin oxidase fromZea mays kernels andVinca rosea crown-gall tissue (1983)
    Springer
    Planta 159 (1983), S. 30-37 
    Details
    ISSN: 1432-2048
    Keywords: Crown gall ; Cytokinin ; Cytokinin oxidase (substrate specificity) ; Vinca ; Zea (cytokinin oxidase)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Cytokinin oxidase has been partially purified from matureZea mays kernels and fromVinca rosea corwn-gall tissue. The molecular weights of the two enzymes, determined by gel filtration, are very different: 94,400 (±10%) forZ. mays and 25,100 (±10%) forV. rosea. Specificity studies have been performed using a large number of synthetic and naturally occurring cytokinins. Only a small number of these compounds serve as substrates and both enzymes exhibit similar substrate specificity. In agreement with other workers, a Δ2 double bond in the N6 side chain is essential for activity. The presence of glucosyl or ribosyl groups in the 7-or 9-position or an alanyl group in the 9-position of the purine moiety have little effect on their susceptibility to cytokinin oxidase, but O-glucosyl derivatives are resistant to oxidation. The relevance of these enzyme systems to studies on cytokinin metabolism and to the endogenous cytokinins is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00998811
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  • 9
    Electronic Resource
    Electronic Resource
    Mass-spectrometric quantification of cytokinin nucleotides and glycosides in tobacco crown-gall tissue (1984)
    Springer
    Planta 161 (1984), S. 345-354 
    Details
    ISSN: 1432-2048
    Keywords: Crown-gall ; Cytokinin in crown-gall ; Mass spectrometry (cytokinins) ; Nicotiana (cytokinins)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract the cytokinins of tobacco crown-gall tissue have been analysed by quantitative mass spectrometry using 2H2-labelled cytokinin riboside 5′-monophosphates and 15N4-labelled cytokinin glycosides as internal standards. The principal endogenous cytokinin of this tissue is zeatin riboside 5′-monophosphate. The biologically inactive 7-glucoside of zeatin is the most abundant basic cytokinin in the tissue. These findings expose the limitations of previously reported analyses of similar tissues, which were restricted to biologically active basic cytokinins. The present study demonstrates that the endogenous cytokinins of tobacco crowngall tissue show a clear correspondence to the range of metabolites formed when exogenous cytokinins are supplied to nontumorous tobacco cells.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00398725
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  • 10
    Electronic Resource
    Electronic Resource
    Endogenous cytokinins in vegetative shoots of peas (1986)
    Springer
    Plant growth regulation 4 (1986), S. 311-323 
    Details
    ISSN: 1573-5087
    Keywords: Pea ; Pisum ; G2 ; senescence ; cytokinin ; zeatin ; zeatin riboside ; zeatin-0-glucoside ; zeatin riboside-0-glucoside ; dihydrozeatin ; dihydrozeatin riboside ; zeatin-7-glucoside ; zeatin-9-glucoside ; mass spectrometry ; selected ion monitoring ; stable isotope dilution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract In G2 peas senescence only takes place in long days. In order to determine the role of cytokinins in this process the endogenous cytokinins from vegetative shoots of G2 peas were characterized using gas chromatography-mass spectroscopy following purification by HPLC. Cytokinins were extracted and purified with and without the addition of 15N labelled internal standards of several cytokinins to estimate cytokin content by isotope dilution in the mass spectra. Samples without internal standards were bioassayed after HPLC. Bioassays showed the presence of zeatin, zeatin riboside and zeatin-0-glucoside. The presence of zeatin was confirmed by its mass spectrum of its permethylated derivative. Tentative identification of zeatin riboside, zeatin-0-glucoside, dihydrozeatin, and dihydrozeatin-0-glucoside was obtained by the coincidence of the major ion for the permethylated natural and 15N labelled internal standards on GC-MS, and the similar coincidence of ions for permethylated zeatin riboside-0-glucoside by direct probe MS. There was no indication of the presence of significant quantities of zeatin-7-glucoside or zeatin-9-glucoside. The amounts in the tissue ranged from 200–1000 ng/kg fresh weight for each cytokinin and about 2–4 μg/kg fresh weight for total cytokinins. There was no apparent difference in the levels in mature but pre-senescent shoots grown in long days and short days indicating that apical senesecence in G2 peas does not appear to be induced by a decline in cytokinin level in the shoots.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00024931
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