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1.
Cytokinin bases (zeatin and dihydrozeatin) and ribosides (zeatin riboside and dihydrozeatin riboside) were identified as major cytokinins in tobacco xylem sap by radioimmunoassay. When 3H-labelled zeatin riboside or dihydrozeatin riboside were supplied to tobacco plants via the xylem, leaves of differing maturity did not differ appreciably in level of radioactivity or in metabolism of the cytokinin. The major metabolites of zeatin riboside in leaves were adenine, adenosine and adenine nucleotides, whereas that of dihydrozeatin riboside was dihydrozeatin 7-glucoside. Incorporation of [14C]adenine into zeatin was evident in upper green leaves. indicating that young leaves have the capacity to synthesize cytokinins in situ. In contrast, fully expanded green leaves and senescing tobacco leaves exhibited little or no incorporation of [14C]adenine into cytokinins. This difference in cytokinin biosynthetic capacity may contribute to the differing cytokinin levels in leaves of different matirity, and may participate in control of sequential leaf senescence in tobacco.  相似文献   

2.
The biosynthesis of free cytokinins in the mevalonic acid auxotrophic Lactobacillus acidophilus , ATCC 4963 has been investigated. After a short pulse labelling with [14C]-mevalonic acid the labelled free cytokinins of bacteria and media and the labelled cytokinin-nucleotide moiety of tRNA and oligonucleotides were determined and compared. tRNA is the main precursor for cytokinin production. Bacteria previously starved for mevalonic acid showed the presence of at least one additional cytokinin precursor. A fraction of oligonudeotides shows rapid incorporation of 14C and contains labelled cytokinin nucleotides. There are no indications for a direct isopentenylation of adenine, adenosine or its phosphate derivatives.  相似文献   

3.
The role of roots in the enhancement of cytokinin content and leaf growth of Phaseolus vulgaris plants after decapitation and partial defoliation was investigated. Partial excision of the roots of plants which were decapitated above the primary leaf node resulted in a reduction of leaf growth and soluble proteins accumulation in the primary leaves. Roots excision was done at time of decapitation and repeated 8 days later. Endogenous cytokinins, known to be involved in enhancing shoot growth, accumulated in the leaves and stems of decapitated and partially defoliated plants. Lower levels of cytokinins were detected in the leaves of decapitated plants with only a partial root system. The level of cytokinins in the roots of decapitated plants was reduced by partial root excision. The growth and accumulation of cytokinins in leaves were, however, not totally suppressed by removing a large proportion of the roots. At the commencement of the experiment the stem had a higher cytokinin content than both the leaves and roots. This suggests that the stem could be an alternative source of cytokinins to the leaves. The cytokinin complement in the leaves of decapitated plants is not identical to that in the roots. It appears that cytokinins supplied by the roots are metabolized in the leaves, or that alternatively certain cytokinins are synthesized in the leaves themselves.  相似文献   

4.
The effect of cytokinins was studied on the incorporation of 14C-labelled precursors into the nucleic acid fraction of protoplasts isolated from callus or roots of Brassica campestris. Protoplasts from callus and roots took up 14C-uridine from the incubation medium and incorporated this precursor into the ribonucleic acid fraction during the experimental period of 16 h. Low concentrations of kinetin (10?8-5 × 10?6M) did not stimulate the incorporation, and kinetin inhibited this process at higher concentrations (5 × 10?5M). This result led to an investigation on the uptake of cytokinins by protoplasts of roots. In contrast to a rapid uptake of radio-actively labelled adenine and uridine. protoplasts from roots took up only small amounts of labelled kinetin. zeatin, zeatin riboside and zeatin nucleotides from the incubation medium. Root sections took up far more adenine and kinetin than protoplasts from roots. The ratio between the amount of kinetin taken up and applied was much higher for the sections than for protoplasts, indicating that intact root cells took up kinetin far more rapidly than protoplasts. It is suggested that the plasmalemma and cell wall play an essential role in the uptake of cytokinins or that the differences in the uptake rates are related to differences between the rates of metabolism of cytokinins in root sections and in protoplasts.  相似文献   

5.
F. Bangerth 《Planta》1994,194(3):439-442
When xylem exudate of previously untreated Phaseolus vulgaris plants was analysed for cytokinins by radioimmunoassay, a low concentration (about 5 ng · ml–1) was found. However, when the plants were decapitated about 16 h before the xylem exudate was collected, an almost 25-fold increase in cytokinin concentration was observed. Twenty-four hours after decapitation this increase even reached 4000 compared to control plants. Applying naphthaleneacetic acid (NAA) to the shoot of decapitated plants almost eliminated the effect of shoot tip removal on cytokinin concentration, suggesting that cytokinins in the xylem exudate of intact plants are under the control of the polar auxin transport system. Other xylem constituents, such as potassium or free amino acids did not show this strong increase after decapitation and did not respond to NAA application. It is concluded that the observed auxin/cytokinin interaction has an important regulatory role to play, not only in apical dominance but in many other correlative events as well.Abbreviations AD apical dominance - CKs cytokinin(s) - iAde/iAdo isopentenyladenine/iospentenyladenosine - NAA naphthaleneacetic acid - Z/ZR zeatin/zeatin riboside  相似文献   

6.
Cytokinins are important purine derivatives that act as hormones to control many processes in plants. Cytokinins such as isopentenyladenine (IPA), kinetin and benzyladenine were very effective at inducing the granulocytic differentiation of human myeloid leukemia HL-60 cells. The metabolism of cytokinins to their nucleotides was closely associated with cytokinin-induced differentiation and growth inhibition. When the cells were incubated with [14C]-benzyladenine, radioactivity was significantly incorporated into RNA and DNA. However, the radioactive nucleotides in RNA or DNA were adenine nucleotides, not benzyladenine nucleotides, suggesting that cytokinins were not incorporated into RNA and DNA. The benzyladenine nucleotides were not stably released into the medium in intact form. Cytokinins effectively induced a phosphorylated (active) form of mitogen-activated protein kinase (MAPK). MAPK activation was necessary for cytokinin-induced differentiation, because PD98059, an inhibitor of MAPK kinase, suppressed the differentiation induced by cytokinins. These results suggest that cytokinin nucleotides themselves play an important role in inducing the differentiation of HL-60 cells.  相似文献   

7.
The growth of the primary leaves of Phaseolus vulgaris L. was enhanced greatly by decapitation of the rest of the shoot. This increased growth was manifested by an increase in leaf area, leaf weight, and in a higher synthesis of chlorophyll and soluble proteins. Within the roots and stems decapitation resulted in a detectable increase in the endogenous cytokinins within 2 days after the surgical treatment. In the primary leaves increased cytokinin levels were only detected after 16 days. At this time most of the recorded activity co-chromatographed with the cytokinin glucosides. When plants which were decapitated were left under normal growing conditions for 16 days and then transferred to continuous darkness for 8 days the senescence of the primary leaves of the decapitated plants, in which the cytokinins had increased, was delayed significantly when compared with that of the primary leaves of the intact plants. the significance of these findings is discussed.  相似文献   

8.
H. Maaß  D. Klämbt 《Planta》1981,151(4):353-358
Roots of intact bean plants were supplied with [14C]adenine by pulse-chase experiments. The rate of incorporation of radioactivity into tRNA and oligonucleotides of roots as well as the content of radioactive labeled cytokinin nucleotides in these RNA fractions were determined. On the average, 1/70 of the radioactivity incorporated into tRNA was localized in N6(2isopentenyl)adenosine. The half life of tRNA was estimated to be 65–70 h. Shortly after the pulse period, oligonucleotides contained zeatin riboside at a ratio of 1:800, on the basis of radioactivity. The half life of these oligonucleotides was determined to be about 8 h. The main free radioactive cytokinin of roots and leaves was zeatin. Comparing the rate of degradation of 14C-labeled tRNA and the oligonucleotides of roots and the rate of appearance of radioactive cytokinins in roots and leaves, we found strong indications for their dependency. The results contradict the hypothesis of de novo synthesis of cytokinins in roots of intact bean plants.Abbreviations AMP adenosine monophosphate - IPA N6(2isopentenyl)adenosine - IPAde N6(2isopentenyl)adenosine - Z zeatin - ZR zeatinriboside - TLC thin-layer chromatography - HPLC high performance liquid chromatography Part of the doctoral thesis, Bonn 1980  相似文献   

9.
Biosynthesis of cytokinin in shoots was examined by growing rootless tobacco (Nicotiana tabacum) plants in vitro. The rootless plants were originated by culturing tobacco callus on a high cytokinin-low auxin medium to induce the formation of plantlets which were then grown on medium without exogenous cytokinin and auxin. The rootless plants supplied with [(14)C]adenine synthesized ethanol-ethyl acetate-water-soluble radioactive components, portions of which had the same chromatographic and electrophoretic mobilities as N(6)-(Delta(2)-isopentenyl)adenine, N(6)-(Delta(2)-isopentenyl)adenosine, 6-(4-hydroxy-3-methyl-2-butenylamino)purine and 6-(4-hydroxy-3-methyl-2-butenylamino)-9-beta-d-ribofuranosylpurine. The total amount of these four major cytokinins was estimated to be present at a concentration of 14 to 23 nanomoles per kilogram of rootless plant. These data indicate that adenine serves as a precursor of the purine moiety of cytokinin molecules and that the cytokinin biosynthetic sites are also located in the shoot in addition to the presumed root sites.  相似文献   

10.
The crown-gall tissue of Vinca rosea converts labelled adenine into cytokinins. The principal initial products appear to be ribosylzeatin phosphates; zeatin and ribosylzeatin are also produced in appreciable quantities. The efficiency of conversion of adenine into cytokinins suggests a pathway of synthesis independent of turnover of tRNA. Isopentenyl adenine or its derivatives do not appear to be intermediates in the conversion of adenine to zeatin compounds. Cytokinins in V. rosea turnover rapidly and further metabolism of zeatin derivatives seems to result in their conversion into glucosides which are the main cytokinin active compounds in the tissue.Abbreviations HPLC high performance liquid chromatography - AMP adenosine monophosphate - TLC thin-layer chromatography - GLC gas-liquid chromatography  相似文献   

11.
Ultra-performance liquid chromatography-tandem mass spectrometry was used to establish the cytokinin profile of the bryophyte Physcomitrella patens (Hedw.) B.S.G.; of 40 analyzed cytokinins, 20 were detected. cis-Zeatin-riboside-O-glucoside, N(6)-(Delta(2)-isopentenyl)adenosine-5'-monophosphate (iPRMP), and trans-zeatin-riboside-O-glucoside were the most abundant intracellular cytokinins. In addition, the aromatic cytokinins N(6)-benzyladenosine (BAR), N(6)-benzyladenine, meta-, and ortho-topolin were detected. Unexpectedly, the most abundant extracellular cytokinin was the nucleotide iPRMP, and its identity was confirmed by quadrupole time-of-flight mass spectrometry. The effects of overexpressing a heterologous cytokinin oxidase/dehydrogenase (CKX; EC 1.4.3.18/1.5.99.12) gene (AtCKX2 from Arabidopsis [Arabidopsis thaliana]) on the intracellular and extracellular distribution of cytokinins was assessed. In cultures of CKX-transformed plants, ultra-performance liquid chromatography-tandem mass spectrometry measurements showed that there were pronounced reductions in the extracellular concentrations of N(6)-(Delta(2)-isopentenyl)adenine (iP) and N(6)-(Delta(2)-isopentenyl)adenosine (iPR), but their intracellular cytokinin concentrations were only slightly affected. In vitro and in vivo measured CKX activity was shown to be strongly increased in the transformants. Major phenotypic changes observed in the CKX-overexpressing plants included reduced and retarded budding, absence of sexual reproduction, and abnormal protonema cells. In bud-induction bioassays with wild-type Physcomitrella, the nucleotides iPRMP, trans-zeatin-riboside-5'-monophosphate, BAR monophosphate, and the cis-zeatin forms cZ and cZR had no detectable effects, while the activities displayed by other selected cytokinins were in the following order: iP > tZ > N(6)-benzyladenine > BAR > iPR > tZR > meta-topolin > dihydrozeatin > ortho-topolin. The results on wild type and CKX transgenics suggest that extracellular iP and iPR are the main cytokinins responsible for inducing buds in the bryophyte Physcomitrella. Cytokinin profile is discussed regarding the evolution of cytokinin biosynthetic pathways.  相似文献   

12.
Decapitated tomato plants were supplied via the roots with [8-14C]-kinetin or [8-14C]-benzyladenine in a nutrient solution for a period of 24 h. After this time the root material, the root sap produced during the 24 h period and the nutrient solution remaining at the end of the experiments were analysed for cytokinins. HPLC techniques and chemical treatments were used to tentatively identify radioactive metabolites formed. Uptake of kinetin and benzyladenine by the roots was found to be limited but once within the root tissues metabolism was both rapid and extensive.At least 14 metabolites of kinetin were recovered from root tissue and root sap. Many of these appeared to be degradation products. There was, however, some evidence of formation of zeatin-like derivatives. Side-chain cleavage of the original kinetin which occurs rapidly is suggested as a possible route for the eventual production of these endogenous cytokinin forms.The benzyladenine taken up by the roots was apparently both ribosylated and glucosylated. No unmetabolized benzyladenine was detected in the root tissues after 24 h. Only very low levels of radioactivity were associated with the retention time of adenine, suggesting that in the case of benzyladenine side-chain cleavage is of limited importance.The significance of these reactions in relation to the potential use of cytokinins in the regulation of plant growth is discussed.  相似文献   

13.
When care was taken to minimise the effects of phosphatase activity during extraction ofVinca rosea crown-gall tumour tissue, a large proportion of extractable cytolinin activity was present in the nucleotide fraction. Analysis using ion-exchange chromatography followed by enzymic or chemical degradation and subsequent identification of the biologically active material indicated that this activity was due to zeatin riboside 5′-monophosphate. This was also the major radiolabelled cytokinin formed when this tissue was supplied with [14C]adenine. The incorporation of radioactivity from [14C]adenosine into free cytokinins was also shown, but no incorporation of radioactivity was found when [3H]mevalonic acid lactone was supplied to this tissue under the same conditions. In parallel experiments using normal stem callus tissue ofV. rosea, no incorporation of [14C]adenine into free cytokinins was observed. The significance of these results is discussed in relation to a possible transfer-RNA-independent pathway of cytokinin biosynthesis, operating primarily at the mononucleotide level.  相似文献   

14.
[3H]Zeatin riboside was supplied to intact pea (Pisum sativum) plants either onto the leaves or onto the root nodules. When applied directly to nodules, approximately 70% of recovered radioactivity remained in the nodules, approximately 15% was detected in the root system, and 15% was in the shoot. However, when supplied to the leaves, little 3H was transported, with approximately 0.05% of recovered radioactivity being found in the root system and nodules. On a fresh weight basis, nodules accumulated more 3H than the parent root. In both types of studies, metabolites with an intact zeatin moiety were detected in root nodules.

In all experiments, two-dimensional thin layer chromatography revealed that little 3H remained as zeatin riboside in root or nodule tissue at the end of the labeling period. Nodules metabolized [3H]zeatin riboside to the following cytokinins/cytokinin metabolites: zeatin, adenosine, adenine, the O-glucosides of zeatin and zeatin riboside, lupinic acid, nucleotides of adenine and zeatin, and the dihydro derivatives of many of these compounds.

Although a few small differences were observed, there were no major differences between root and nodule tissue in their metabolism of [3H] zeatin riboside. Furthermore, any differences between effective and ineffective nodules were generally minor.

  相似文献   

15.
Cytokinins in Populus×robusta: Qualitative Changes during Development   总被引:1,自引:0,他引:1  
Qualitative changes of cytokinins in leaves of different ages from Populus x robusta (Schneid.) have been determined, together with seasonal changes in cytokinin activity in mature leaves and xylem sap. Chromatography on Sephadex LH-20 has shown that total cytokinin activity and diversity are at a maximum in expanding leaves. As leaves age, the amount and number of cytokinins decrease, with yellow senescent leaves having only one detectable cytokinin, thought to be a glucoside. Seasonal changes were followed by chromatography of the extracts on paper in butan-2-ol: 25 % NH4OH (4:1). Maximum cytokinin levels, due to Fraction Z (Rf 0.5–0.8), in leaves and xylem sap were found in mid-summer. Prior and subsequent to cessation of shoot elongation growth, fraction Z decreased and fraction N (Rf 0–0.2) increased to predominate in senescent leaves. Removal of the apex resulted in an increase of fraction N in leaves from decapitated plants when compared to similar leaves from intact plants. It is suggested that, once apical sink activity has ceased, cytokinins in the xylem sap are diverted into leaves and converted to a cytokinin glucoside, possibly a storage form of the hormone.  相似文献   

16.
The ipt gene from the T-DNA of Agrobacterium tumefaciens was transferred to tobacco (Nicotiana tabacum L.) in order to study the control which auxin appears to exert over levels of cytokinin generated by expression of this gene. The transgenic tissues contained elevated levels of cytokinins, exhibited cytokinin and auxin autonomy and grew as shooty calli on hormone-free media. Addition of 1-naphthylacetic acid to this culture medium reduced the total level of cytokinins by 84% while 6-benzylaminopurine elevated the cytokinin level when added to media containing auxin. The cytokinins in the transgenic tissue were labelled with 3H and auxin was found to promote conversion of zeatin-type cytokinins to 3H-labelled adenine derivatives. When the very rapid metabolism of exogenous [3H]zeatin riboside was suppressed by a phenylurea derivative, a noncompetitive inhibitor of cytokinin oxidase, auxin promoted metabolism to adenine-type compounds. Since these results indicated that auxin promoted cytokinin oxidase activity in the transformed tissue, this enzyme was purified from the tobacco tissue cultures. Auxin did not increase the level of the enzyme per unit tissue protein, but did enhance the activity of the enzyme in vitro and promoted the activity of both glycosylated and non-glycosylated forms. This enhancement could contribute to the decrease in cytokinin level induced by auxin. Studies of cytokinin biosynthesis in the transgenic tissues indicated that trans-hydroxylation of isopentenyladenine-type cytokinins to yield zeatin-type cytokinins occurred principally at the nucleotide level.Abbreviations Ade adenine - Ados adenosine - BA 6-benzylaminopurine - C control - Con A concanavallin A - CP cellulose phosphate - IPT isopentenyl transferase - NAA 1-naphthylacetic acid - NP normal phase - NPPU N-(3-nitrophenyl)-N-phenylurea - RIA radioimmunoassay - RP reversed phase We wish to thank Dr. J. Zwar for supplying phenylurea derivitives.  相似文献   

17.
Following uptake of [(3)H]zeatin riboside and [(3)H]dihydrozeatin riboside by girdled lupin (Lupinus angustifolius L.) stems via the transpiration stream, rapid lateral movement of the radioactivity from xylem to bark was observed. Short-term studies with intact stems, and other studies with excised stem tissues, revealed that the ribosides and/or the corresponding nucleotides were the cytokinin forms which actually moved into the bark tissues. Relative to cytokinin metabolism in xylem plus pith, metabolism in bark was both more rapid and more complex. Riboside cleavage and formation of the O-acetylzeatin and O-acetyldihydrozeatin ribosides and nucleotides were almost completely confined to bark tissues. Exogenous (3)H-labelled O-acetylzeatin riboside was converted to zeatin riboside in bark tissue, but the presence of the acetyl group suppressed degradation to adenine metabolites. The sequestration and modification of xylem cytokinins by stem tissues probably contributes significantly to the cytokinin status of the shoot. New cytokinins identified by mass spectrometry in lupin were: O-acetyldihydrozeatin 9-riboside, a metabolite of exogenous dihydrozeatin riboside in stem bark; O-methylzeatin nucleotide and O-methyldihydrozeatin 9-riboside, metabolites of endogenous cytokinins in stem bark; O-methylzeatin nucleotide and O-methylzeatin 9-riboside, metabolites of exogenous zeatin riboside in excised pod walls.  相似文献   

18.
Genetic tumour tissues of Nicotiana glauca (Grah.) × N. langsdorffii (Weinm.), which grow on auxin and cytokinin-free medium, were incubated with [14C]-/[3H]-adenine or [3H]-hypoxanthine to investigate cytokinin biosynthesis. Adenine was supplied to tissues of two different ages (2- and 3.5-week-old) for 8, 24 or 30 h. The uptake was over 91.0 % (of "supplied radioactivity") by 2-week-old tissues as compared to around 50.0 % uptake by 3.5-week-old tissues. Incorporation into cytokinins could not be detected. While unmetabolized adenine accounted for only about 24.0 and 13.4 % of "extracted radioactivity" (following 8 and 30 h incubation, respectively) in 2-week-old tissues, relatively higher levels, i.e. 36.0 and 34.5 % (following 8 and 24 h incubation, respectively) were present in 3.5-week-old tissues. The metabolites formed were adenosine and its nucleotides (4.5 - 16.5 % and 37.4 - 60.2 % of the extracted radioactivity, respectively). Hypoxanthine was supplied to 3.5-week-old tissues for 8 and 24 h. While the uptake was low (<28.0 % of supplied radioactivity), the major proportion of extracted radioactivity was due to unmetabolized hypoxanthine (79.8 % and 85.9 % after 8 and 24 h incubation periods, respectively); the minor metabolites were inosine and adenosine (both <0.5 %) and their nucleotides (< 3.5 %). Radioactivity incorporation into cytokinins from hypoxanthine was not detected. Thus in the present investigations precursor incorporation from either adenine or hypoxanthine into cytokinins could not be demonstrated. It is possible that this may be due to slow rate of cytokinin turnover in these tissues.  相似文献   

19.
Li CH  Yu N  Jiang SM  Shangguan XX  Wang LJ  Chen XY 《Planta》2008,228(1):125-136
S-adenosyl-L: -homocysteine hydrolase (SAHH) is a key enzyme for maintenance of cellular transmethylation potential. Although a cytokinin-binding activity had been hypothesized for SAHH, the relation between cytokinin and transmethylation reactions has not been elucidated. Here we show that, of the two Arabidopsis thaliana SAHH genes, AtSAHH1 has a much higher expression level than AtSAHH2. A T-DNA insertion mutant of AtSAHH1 (sahh1-1) and the RNA interference (RNAi) plants (dsAtSAHH2) accumulated a higher level of cytokinins, exhibited phenotypic changes similar to those of cytokinin-overproducers, and their global DNA methylation status was reduced. On the other hand, cytokinins positively regulate the transmethylation pathway genes, including AtSAHH1, AtADK1 (for adenosine kinase), and this regulation involves the cytokinin activity. Furthermore, expression of three cytosine DNA methyltransferase genes examined was inducible by cytokinin treatment. Unlike adenine and adenosine which are SAHH inhibitors, the adenine-type cytokinins have no effect on SAHH activity at protein level. Changing of endogenous cytokinin levels by transgene expression resulted in alterations of DNA methylation status in the sahh1-1 background, suggesting that cytokinins promote DNA methylation, at least under transmethylation stringent conditions. These data demonstrate that the phytohormone cytokinin plays a role in promoting transmethylation reactions, including DNA methylation.  相似文献   

20.
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.  相似文献   

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