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1.
2.
Brian A. McGaw Roger Horgan Jim K. Heald George J. Wullems Rob A. Schilperoort 《Planta》1988,176(2):230-234
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.Abbreviations IAA
indole-3-acetic acid
- SIM
selected ion monitoring
- Z
zeatin
- [7G]Z
zeatin-7-glucoside
- [9R]Z
zeatin-9-riboside
- [9R-5P]Z
zeatin riboside-5-monophosphate 相似文献
3.
The stability of [3H]zeatin riboside supplied to freshly excised tobacco pith explants was found to be inversely related to -naphthaleneacetic acid concentration in the incubation medium. At higher concentrations of -naphthaleneacetic acid greater breakdown of [3H]zeatin riboside was indicated by higher levels of degradative metabolites (adenine, adenosine and adenosine nucleotides) formed. This auxin effect on cytokinin metabolism appears to be mediated, at least in part, through cytokinin oxidase. The results of in-vitro assays carried out with partially purified enzyme from corn kernels substantiale this conclusion. These findings are discussed in relation to recent observations of auxin and cytokinin levels in crown-gall tumours with altered morphology.Abbreviations FPLC
fast protein liquid chromatography
- HPLC
high-performance liquid chromatography
- IP
isopentenyladenine
- NAA
naphthaleneacetic acid
- ZR
zeatin riboside 相似文献
4.
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. 相似文献
5.
Carotenoid and abscisic acid (ABA) levels were determined in endosperm, embryos and seedlings of wild-type and viviparous (vp) mutants ofZea mays L. Carotenoid concentrations were determined by absorption spectrometry following purification by high-performance liquid chromatography and ABA concentrations by combined gas chromatography-mass spectrometry. Lutein and zeaxanthin were the terminal carotenoids in wild-type tissue. The carotenoid profiles ofvp-1 andvp-8 tissue were similar to that of the wild type; invp-2, vp-5, vp-7 andvp-9 carotenogenesis was blocked at early stages so that xanthophylls were absent. Except forvp-1, where the ABA content was similar to the wild type, the ABA content ofvp embryos was substantially reduced, to 6–16% of the corresponding wild type. Thus, the absence of xanthophylls was associated with reduced ABA content, which was in turn correlated with vivipary. Kernels ofvp-8 had a reduced ABA content although xanthophylls were present. Seedlings of carotenoid-deficient mutants rescued from viviparous kernels contained less ABA than did wild-type seedlings grown in the same way. Furthermore, the ABA concentration of such seedlings did not increase in response to water deficit. Conversely,vp-1 seedlings contained normal levels of carotenoids and ABA. Carotenoid-deficient seedlings did not contain appreciable amounts of chlorophyll so that chloroplast development was not normal. Thus ABA-deficiency could be associated with abnormal plastid development rather than the absence of carotenoids per se.Abbreviations ABA
abscisic acid
- DAP
days after pollination
- i.d.
internal diameter
- FW
fresh weight
- GC-MS
combined gas chromatography-mass spectrometry
- HPLC
high-performance liquid chromatography
- MS
mass spectrometry
-
vp
viviparous 相似文献
6.
Abscisic acid-β-D-glucopyranosyl ester (ABAGE) has been measured in several plant species using 2H-labelled ABAGE as an internal standard. The effects of water stress on the levels of ABAGE and its possible physiological role are discussed. Some chemical properties of ABAGE are described. 相似文献
7.
The complement-mediated binding of soluble antibody/dsDNA immune complexes to human neutrophils 总被引:2,自引:0,他引:2
R P Taylor J Burge C Horgan D M Shasby 《Journal of immunology (Baltimore, Md. : 1950)》1983,130(6):2656-2662
The complement-mediated binding of soluble antibody/3H-dsDNA immune complexes (prepared in vitro) to human polymorphonuclear leukocytes (PMN) has been investigated quantitatively. Studies with isolated complement components in conjunction with experiments on the binding of these complexes to human red blood cells suggest that the binding to both cell types is mediated predominantly by CR1 (C4b-C3b) receptors but that CR3 (iC3b or C3d-g) receptors may play a role in binding to PMN but probably not to RBC. Our results also indicate that under the standard conditions of these assays (37 degrees C, 20 to 40 min incubations) there is no significant internalization of the soluble antibody/dsDNA immune complexes after they are bound by the PMN. 相似文献
8.
9.
Alterations of Endogenous Cytokinins in Transgenic Plants Using a Chimeric Isopentenyl Transferase Gene 总被引:3,自引:0,他引:3 下载免费PDF全文
Cytokinins, a class of phytohormones, appear to play an important role in the processes of plant development. We genetically engineered the Agrobacterium tumefaciens isopentenyl transferase gene, placing it under control of a heat-inducible promoter (maize hsp70). The chimeric hsp70 isopentenyl transferase gene was transferred to tobacco and Arabidopsis plants. Heat induction of transgenic plants caused the isopentenyl transferase mRNA to accumulate and increased the level of zeatin 52-fold, zeatin riboside 23-fold, and zeatin riboside 5[prime]-monophosphate twofold. At the control temperature zeatin riboside and zeatin riboside 5[prime]-monophosphate in transgenic plants accumulated to levels 3 and 7 times, respectively, over levels in wild-type plants. This uninduced cytokinin increase affected various aspects of development. In tobacco, these effects included release of axillary buds, reduced stem and leaf area, and an underdeveloped root system. In Arabidopsis, reduction of root growth was also found. However, neither tobacco nor Arabidopsis transgenic plants showed any differences relative to wild-type plants in time of flowering. Unexpectedly, heat induction of cytokinins in transgenic plants produced no changes beyond those seen in the uninduced state. The lack of effect from heat-induced increases could be a result of the transient increases in cytokinin levels, direct or indirect induction of negating factor(s), or lack of a corresponding level of competent cellular factors. Overall, the effects of the increased levels of endogenous cytokinins in non-heat-shocked transgenic plants seemed to be confined to aspects of growth rather than differentiation. Since no alterations in the programmed differentiation pattern were found with increased cytokinin levels, this process may be controlled by components other than absolute cytokinin levels. 相似文献
10.
Huaibi Zhang Kathryn Joan Horgan Paul Hugh Stewart Reynolds Paula Elizabeth Jameson 《Physiologia plantarum》2003,117(2):264-269
Cytokinins (CKs) play essential roles in the regulation of plant growth and development. In the previous paper (Zhang et al. 2001), we reported the detection and identification of a wide spectrum of CKs, including several novel forms, in the buds of Pinus radiata D. Don. In this paper we examine the relationship between the CKs and buds from juvenile and adult trees of P. radiata. During development the morphology of buds alters significantly, from buds bearing primary needles during their juvenile phase to buds sealed in scales at the adult phase. The morphology of adult buds is a very stable character, as fascicle meristems released from apical dominance, or cultured in vitro, produced only secondary needles. However, exogenous CK causes the adult buds to revert to juvenile bud development in vitro . Analyses of the endogenous CKs revealed that juvenile buds had a relatively higher level of isopentenyladenine and isopentenyladenosine, extremely low levels of phosphorylated CKs and a relatively low level of novel CK glycosides. The adult buds contained lower levels of free base and riboside CKs but very high levels of phosphorylated CKs and novel CK glycosides. Possible roles for CKs in the regulation of bud development are discussed. 相似文献