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  • 1
    Electronic Resource
    Electronic Resource
    Increased cytokinin levels in transgenic PSAG12–IPT tobacco plants have large direct and indirect effects on leaf senescence, photosynthesis and N partitioning (2000)
    Oxford, UK : Blackwell Science Ltd
    Plant, cell & environment 23 (2000), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: We studied the impact of delayed leaf senescence on the functioning of plants growing under conditions of nitrogen remobilization. Interactions between cytokinin metabolism, Rubisco and protein levels, photosynthesis and plant nitrogen partitioning were studied in transgenic tobacco (Nicotiana tabacum L.) plants showing delayed leaf senescence through a novel type of enhanced cytokinin syn-thesis, i.e. targeted to senescing leaves and negatively auto-regulated (PSAG12–IPT), thus preventing developmental abnormalities. Plants were grown with growth-limiting nitrogen supply. Compared to the wild-type, endogenous levels of free zeatin (Z)- and Z riboside (ZR)-type cytokinins were increased up to 15-fold (total ZR up to 100-fold) in senescing leaves, and twofold in younger leaves of PSAG12–IPT. In these plants, the senescence-associated declines in N, protein and Rubisco levels and photosynthesis rates were delayed. Senescing leaves accumulated more (15N-labelled) N than younger leaves, associated with reduced shoot N accumulation (–60%) and a partially inverted canopy N profile in PSAG12–IPT plants. While root N accumulation was not affected, N translocation to non-senescing leaves was progressively reduced. We discuss potential consequences of these modified sink–source relations, associated with delayed leaf senescence, for plant productivity and the efficiency of utilization of light and minerals.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-3040.2000.00544.x
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  • 2
    Electronic Resource
    Electronic Resource
    The synthesis of allylic phosphate derivatives of trans zeatin
    Amsterdam : Elsevier
    Tetrahedron 45 (1989), S. 3889-3896 
    Details
    ISSN: 0040-4020
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/S0040-4020(01)89248-6
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    8-14C-Zeatin metabolites and their transport from leaf to phloem exudate of Yucca (1981)
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 52 (1981), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Transport and metabolism of 8-14 C-zeatin, applied to an attached de-tipped one-year-old mature leaf of a Yucca plant bearing a bleeding inflorescent stalk, has been studied. Radioactive zeatin ribotide was found in the exudate of the bleeding inflorescence, which was collected over a period of 5 days. Radioactive zeatin ribotide was mainly extracted from the fed leaf. Minor conversion products in this leaf were zeatin ribotide, zeatin-o-β-glucoside and zeatinriboside o-β-glucoside.In not zeatin fed plants, zeatin-o-β-glucoside was tentatively identified as the main endogenous cytokinin in one-year-old mature leaves. In the bleeding sap of not treated plants no free bases of zeatin or zeatin ribosides were found. After alkaline phosphatase treatment zeatin-riboside was detected by combined gas chromatography-mass spectrometry, indicating the presence of zeatin ribotide in the bleeding sap. High β-glucosidase activity was found in the stern.Results suggest that stared cytokinin glucosides from Yucca leaves are, converted by β-glucosidase in leaves and stem, transported through the inflorescent stalk as zeatin nucleotides.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1399-3054.1981.tb06041.x
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  • 4
    Electronic Resource
    Electronic Resource
    The role of cytokinins in relation to flower-bud blasting in Iris cv. Ideal: Cytokinin determination by an improved enzyme-linked immunosorbent assay (1986)
    Springer
    Plant growth regulation 4 (1986), S. 65-74 
    Details
    ISSN: 1573-5087
    Keywords: Flower-bud blasting ; Iris ; cytokinins ; EIA
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The effect of dark and light treatment on endogenous cytokinins in internodes and buds of Iris was determined. Plant material was purified by chromatographic methods and cytokinins were assayed by an immunoassay. An indirect competitive enzyme immunoassay for the determination of zeatin- and isopentenyl-adenine cytokinins was developed. This assay, which is not dependent on the titre of the antibodies raised against zeatin riboside and isopentenyl-adenosine appeared to be specific, highly sensitive and more reproducible compared to a direct competitive enzyme immunoassay for cytokinins. Isopentenyl-adenosine was the most abundant cytokinin found, followed by zeatin: the latter counteracts bud blast when injected into dark-treated plants. Smaller amounts of isopentenyl-adenine and zeatin riboside were found. Results are in agreement with the hypothesis that deficiency of growth substances like cytokinins plays an important role in the occurrence of flower-bud blasting. A possible role for the major endogenous cytokinin, isopentenyl-adenosine, which earlier was found not to be effective in counteracting bud blast when injected into buds of dark-treated plants, is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00025350
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    Paper (German National Licenses)
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  • 5
    Electronic Resource
    Electronic Resource
    Formation of zeatin allylic phosphate by the microsomal fractions of bulb disks of Iris × hollandica Tub. and tubers of Helianthus tuberosus L. (1989)
    Springer
    Plant growth regulation 8 (1989), S. 263-276 
    Details
    ISSN: 1573-5087
    Keywords: Cytokinin ; Zeatin nucleotide ; Iris × hollandica Tub. ; Helianthus tuberosus L.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract It is shown that in bulbous Iris zeatin originates from a nucleotide. This nucleotide is probably zeatin-allylic-phosphate, in which a phosphate group is attached to the isoprenoid side-chain of zeatin. The formation of zeatin-allylic-phosphate from t-zeatin and 8-[14C]-zeatin by the microsomal fractions of Iris bulb disks and Helianthus tubers was demonstrated. The responsible enzyme was partially purified. 5′-AMP was found to be a phosphate group delivering substrate. Adenosine and adenine inhibited the enzyme reaction. The significance of the results is discussed in relation to cytokinin biosynthesis and the occurrence of bud blast in Iris.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00025396
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    Paper (German National Licenses)
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