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Hošek P, Hoyerová K, Kiran NS, Dobrev PI, Zahajská L, Filepová R, Motyka V, Müller K, Kamínek M. Distinct metabolism of N-glucosides of isopentenyladenine and trans-zeatin determines cytokinin metabolic spectrum in Arabidopsis. THE NEW PHYTOLOGIST 2020; 225:2423-2438. [PMID: 31682013 DOI: 10.1111/nph.16310] [Citation(s) in RCA: 35] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/28/2019] [Accepted: 10/26/2019] [Indexed: 05/10/2023]
Abstract
The diversity of cytokinin (CK) metabolites suggests their interconversions are the predominant regulatory mechanism of CK action. Nevertheless, little is known about their directionality and kinetics in planta. CK metabolite levels were measured in 2-wk-old Arabidopsis thaliana plants at several time points up to 100 min following exogenous application of selected CKs. The data were then evaluated qualitatively and by mathematical modeling. Apart from elevated levels of trans-zeatin (tZ) metabolites upon application of N6 -(Δ2 -isopentenyl)adenine (iP), we observed no conversions between the individual CK-types - iP, tZ, dihydrozeatin (DHZ) and cis-zeatin (cZ). In particular, there was no sign of isomerization between tZ and cZ families. Also, no increase of DHZ-type CKs was observed after application of tZ, suggesting low baseline activity of zeatin reductase. Among N-glucosides, those of iP were not converted back to iP while tZ N-glucosides were cleaved to tZ bases, thus affecting the whole metabolic spectrum. We present the first large-scale study of short-term CK metabolism kinetics and show that tZ N7- and N9-glucosides are metabolized in vivo. We thus refute the generally accepted hypothesis that N-glucosylation irreversibly inactivates CKs. The subsequently constructed mathematical model provides estimates of the metabolic conversion rates.
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Affiliation(s)
- Petr Hošek
- The Czech Academy of Sciences, Institute of Experimental Botany, Rozvojová 263, 165 02, Praha 6, Czech Republic
| | - Klára Hoyerová
- The Czech Academy of Sciences, Institute of Experimental Botany, Rozvojová 263, 165 02, Praha 6, Czech Republic
| | - Nagavalli S Kiran
- The Czech Academy of Sciences, Institute of Experimental Botany, Rozvojová 263, 165 02, Praha 6, Czech Republic
| | - Petre I Dobrev
- The Czech Academy of Sciences, Institute of Experimental Botany, Rozvojová 263, 165 02, Praha 6, Czech Republic
| | - Lenka Zahajská
- The Czech Academy of Sciences, Institute of Experimental Botany, Rozvojová 263, 165 02, Praha 6, Czech Republic
| | - Roberta Filepová
- The Czech Academy of Sciences, Institute of Experimental Botany, Rozvojová 263, 165 02, Praha 6, Czech Republic
| | - Václav Motyka
- The Czech Academy of Sciences, Institute of Experimental Botany, Rozvojová 263, 165 02, Praha 6, Czech Republic
| | - Karel Müller
- The Czech Academy of Sciences, Institute of Experimental Botany, Rozvojová 263, 165 02, Praha 6, Czech Republic
| | - Miroslav Kamínek
- The Czech Academy of Sciences, Institute of Experimental Botany, Rozvojová 263, 165 02, Praha 6, Czech Republic
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Juras MCR, Jorge J, Pescador R, Ferreira WDM, Tamaki V, Suzuki RM. In vitro culture and acclimatization of Cattleya xanthina (Orchidaceae), an endangered orchid of the Brazilian Atlantic Rainforest. RODRIGUÉSIA 2019. [DOI: 10.1590/2175-7860201970014] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 08/30/2023]
Abstract
Abstract Cattleya xanthina is a Neotropical orchid endemic to the Brazilian Atlantic Rainforest, at high risk of extinction. In this paper, we investigated the effects of different culture media on C. xanthina as well as on their endogenous nitrogen status. Culture media studied: Knudson C (KC), Vacin and Went (VW), and Murashige and Skoog (MS), the latter used at two different concentration (full and half-strength; MS/2). After 180 days, plants were transferred to MS medium with different NAA and BA concentrations. In each treatment, biometric parameters were measured and the endogenous levels of photosynthetic pigments, total protein, nitrate and ammonium ions were quantified. Plants grown on KC medium had the lowest concentration of nitrogen but exhibited the greatest shoot development, production of photosynthetic pigments and total protein. Results of growth regulators showed that the highest concentration of auxin stimulated root development and the production of photosynthetic pigments, and that a higher concentration of cytokinin promoted protein synthesis and the development of shoots. Most successful acclimatization was obtained when a mixture of Sphagnum and Pinus bark was used as the substrate.
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Goggin DE, Emery RJN, Kurepin LV, Powles SB. A potential role for endogenous microflora in dormancy release, cytokinin metabolism and the response to fluridone in Lolium rigidum seeds. ANNALS OF BOTANY 2015; 115:293-301. [PMID: 25471097 PMCID: PMC4551082 DOI: 10.1093/aob/mcu231] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/08/2014] [Revised: 10/07/2014] [Accepted: 10/09/2014] [Indexed: 05/05/2023]
Abstract
BACKGROUND AND AIMS Dormancy in Lolium rigidum (annual ryegrass) seeds can be alleviated by warm stratification in the dark or by application of fluridone, an inhibitor of plant abscisic acid (ABA) biosynthesis via phytoene desaturase. However, germination and absolute ABA concentration are not particularly strongly correlated. The aim of this study was to determine if cytokinins of both plant and bacterial origin are involved in mediating dormancy status and in the response to fluridone. METHODS Seeds with normal or greatly decreased (by dry heat pre-treatment) bacterial populations were stratified in the light or dark and in the presence or absence of fluridone in order to modify their dormancy status. Germination was assessed and seed cytokinin concentration and composition were measured in embryo-containing or embryo-free seed portions. KEY RESULTS Seeds lacking bacteria were no longer able to lose dormancy in the dark unless supplied with exogenous gibberellin or fluridone. Although these seeds showed a dramatic switch from active cytokinin free bases to O-glucosylated storage forms, the concentrations of individual cytokinin species were only weakly correlated to dormancy status. However, cytokinins of apparently bacterial origin were affected by fluridone and light treatment of the seeds. CONCLUSIONS It is probable that resident microflora contribute to dormancy status in L. rigidum seeds via a complex interaction between hormones of both plant and bacterial origin. This interaction needs to be taken into account in studies on endogenous seed hormones or the response of seeds to plant growth regulators.
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Affiliation(s)
- Danica E Goggin
- School of Plant Biology, University of Western Australia, 35 Stirling Highway, Crawley 6009, Australia, Biology Department, Trent University, 1600 West Bank Drive, Peterborough K9J7B8, Canada and Department of Biology, Western University, 1151 Richmond Street, London N6A3K7, Canada
| | - R J Neil Emery
- School of Plant Biology, University of Western Australia, 35 Stirling Highway, Crawley 6009, Australia, Biology Department, Trent University, 1600 West Bank Drive, Peterborough K9J7B8, Canada and Department of Biology, Western University, 1151 Richmond Street, London N6A3K7, Canada
| | - Leonid V Kurepin
- School of Plant Biology, University of Western Australia, 35 Stirling Highway, Crawley 6009, Australia, Biology Department, Trent University, 1600 West Bank Drive, Peterborough K9J7B8, Canada and Department of Biology, Western University, 1151 Richmond Street, London N6A3K7, Canada
| | - Stephen B Powles
- School of Plant Biology, University of Western Australia, 35 Stirling Highway, Crawley 6009, Australia, Biology Department, Trent University, 1600 West Bank Drive, Peterborough K9J7B8, Canada and Department of Biology, Western University, 1151 Richmond Street, London N6A3K7, Canada
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Choi YI, Noh EW, Kim HJ, Park WJ. Differential regulation of cytokinin oxidase genes and cytokinin-induced auxin biosynthesis by cellular cytokinin level in transgenic poplars. PLANT CELL REPORTS 2014; 33:1737-1744. [PMID: 25048021 DOI: 10.1007/s00299-014-1652-1] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/08/2014] [Revised: 06/24/2014] [Accepted: 06/29/2014] [Indexed: 06/03/2023]
Abstract
The present work with transgenic poplar lines producing varying levels of trans -zeatin suggests the existence of a switching threshold for triggering ckx gene expression or suppressing cytokinin-induced auxin. Cytokinins have an important role in growth and developmental processes of plants. Transgenic plants with varying levels of cellular cytokinin are convenient tools for studying its role in morphogenetic as well as molecular responses. In this work, the transgenic lines producing either high level of cellular trans-zeatin (HX lines) or moderate level (MX lines) were compared with regard to their cytokinin oxidase activities and cellular auxin content. The HX lines showed typical cytokinin phenotypes including leafy shoots and spontaneous shoot formation on hormone free medium. In contrast, the MX lines did not show any striking phenotypes. However, in leaf disk culture on hormone free medium, they regenerated roots and subsequently formed shoots from the roots. Determination of cellular IAA content revealed a significant increase in the level in MX lines but not in HX lines. Of nine cytokinin oxidase genes (ckx) examined by qPCR, five were activated in HX lines but not in MX lines. Among them, ckx4 appeared to play a key role in maintaining cellular cytokinin level since it showed more than 1,000-fold increase in HX lines and in the leaf disks of untransformed control exposed to exogenous cytokinins. Although low level of cellular cytokinin did not induce the expression of ckx genes, it appeared to trigger cellular IAA biosynthesis.
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Affiliation(s)
- Young Im Choi
- Forest Biotechnology Division, Korea Forest Research Institute, Suwon, Gyeonggi do, 441-847, Republic of Korea,
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Kiran NS, Benková E, Reková A, Dubová J, Malbeck J, Palme K, Brzobohatý B. Retargeting a maize β-glucosidase to the vacuole--evidence from intact plants that zeatin-O-glucoside is stored in the vacuole. PHYTOCHEMISTRY 2012; 79:67-77. [PMID: 22552277 DOI: 10.1016/j.phytochem.2012.03.012] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/17/2012] [Revised: 03/05/2012] [Accepted: 03/23/2012] [Indexed: 05/31/2023]
Abstract
Cytokinin (CK) activity is regulated by the complex interplay of their metabolism, transport, stability and cellular/tissue localization. O-glucosides of zeatin-type CKs are postulated to be storage and/or transport forms. Active CK levels are determined in part by their differential distribution of CK metabolites across different subcellular compartments. We have previously shown that overexpressing chloroplast-localized Zm-p60.1, a maize β-glucosidase capable of releasing active cytokinins from their O- and N3-glucosides, perturbs CK homeostasis in transgenic tobacco. We obtained tobacco (Nicotiana tabacum L., cv Petit Havana SR1) plants overexpressing a recombinant Zm-p60.1 that is targeted to the vacuole. The protein is correctly processed and localized to the vacuole. When grown on medium containing exogenous zeatin, transgenic seedlings rapidly accumulate fresh weight due to ectopic growths at the base of the hypocotyl. The presence of the enzyme in these ectopic structures is shown by histochemical staining. CK quantification reveals that these transgenic seedlings are unable to accumulate zeatin-O-glucoside to levels similar to those observed in the wild type. When crossed with tobacco overexpressing the zeatin-O-glucosyltransferase gene from Phaseolus, the vacuolar variant shows an almost complete reversion in the root elongation assay. This is the first evidence from intact plants that the vacuole is the storage organelle for CK O-glucosides and that they are available to attack by Zm-p60.1. We propose the use of Zm-p60.1 as a robust molecular tool that exploits the reversibility of O-glucosylation and enables delicate manipulations of active CK content at the cellular level.
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Affiliation(s)
- Nagavalli S Kiran
- Department of Molecular Biology and Radiobiology, Faculty of Agronomy, Mendel University in Brno, Zemědělská 1, CZ-61300 Brno, Czech Republic
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Yuldashev R, Avalbaev A, Bezrukova M, Vysotskaya L, Khripach V, Shakirova F. Cytokinin oxidase is involved in the regulation of cytokinin content by 24-epibrassinolide in wheat seedlings. PLANT PHYSIOLOGY AND BIOCHEMISTRY : PPB 2012; 55:1-6. [PMID: 22480990 DOI: 10.1016/j.plaphy.2012.03.004] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/21/2012] [Accepted: 03/05/2012] [Indexed: 05/05/2023]
Abstract
Fast and stable 2-fold accumulation of cytokinins (CKs) was detected initially in roots and then in shoots of 4-day-old wheat (Triticum aestivum L.) seedlings in the course of their treatment with 0.4μM 24-epibrassinolide (EBR). Elevated cytokinin level has been maintained only in the presence of EBR, while the hormone removal has led to return of cytokinin concentration to the control level initially in the roots and then in the shoots. EBR-induced accumulation of cytokinins was accompanied by inhibition of both cytokinin oxidase (CKX) (cytokinin oxidase/dehydrogenase, EC 1.5.99.12) activity and expression of the gene coding for this enzyme, and on the contrary the decline in CKs level resulted in increase in these characteristics up to the control level in roots and then in shoots. Sharp accumulation of cytokinin O-glucosides has been discovered in response to EBR-treatment suggesting fast EBR-induced activation of production of cytokinins, which excessive amounts were transferred into the storage forms. The obtained data provide evidence for the involvement of EBR in regulation of cytokinin level in wheat seedlings.
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Affiliation(s)
- Ruslan Yuldashev
- Institute of Biochemistry and Genetics, Ufa Scientific Centre, Russian Academy of Sciences, Pr. Oktyabrya 71, Ufa 450054, Russia
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Taglienti A, Sequi P, Cafiero C, Cozzolino S, Ritota M, Ceredi G, Valentini M. Hayward kiwifruits and Plant Growth Regulators: Detection and effects in post-harvest studied by Magnetic Resonance Imaging and Scanning Electron Microscopy. Food Chem 2011. [DOI: 10.1016/j.foodchem.2010.11.050] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Černý M, Dyčka F, Bobál'ová J, Brzobohatý B. Early cytokinin response proteins and phosphoproteins of Arabidopsis thaliana identified by proteome and phosphoproteome profiling. JOURNAL OF EXPERIMENTAL BOTANY 2011; 62:921-37. [PMID: 20974740 PMCID: PMC3022391 DOI: 10.1093/jxb/erq322] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/12/2010] [Revised: 08/24/2010] [Accepted: 09/21/2010] [Indexed: 05/20/2023]
Abstract
Cytokinins are plant hormones involved in regulation of diverse developmental and physiological processes in plants whose molecular mechanisms of action are being intensely researched. However, most rapid responses to cytokinin signals at the proteomic and phosphoproteomic levels are unknown. Early cytokinin responses were investigated through proteome-wide expression profiling based on image and mass spectrometric analysis of two-dimensionally separated proteins and phosphoproteins. The effects of 15 min treatments of 7-day-old Arabidopsis thaliana seedlings with four main cytokinins representing hydroxyisopentenyl, isopentenyl, aromatic, and urea-derived type cytokinins were compared to help elucidate their common and specific function(s) in regulating plant development. In proteome and phosphoproteome maps, significant differences were reproducibly observed for 53 and 31 protein spots, respectively. In these spots, 96 proteins were identified by matrix-assisted laser desorption/ionization time-of-flight/time-of-flight mass spectrometry (MALDI-TOF/TOF MS), providing a snapshot of early links in cytokinin-regulated signalling circuits and cellular processes, including light signalling and photosynthesis, nitrogen metabolism, the CLAVATA pathway, and protein and gene expression regulation, in accordance with previously described cytokinin functions. Furthermore, they indicate novel links between temperature and cytokinin signalling, and an involvement of calcium ions in cytokinin signalling. Most of the differentially regulated proteins and phosphoproteins are located in chloroplasts, suggesting an as yet uncharacterized direct signalling chain responsible for cytokinin action in chloroplasts. Finally, first insights into the degree of specificity of cytokinin receptors on phosphoproteomic effects were obtained from analyses of cytokinin action in a set of cytokinin receptor double mutants.
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Affiliation(s)
- Martin Černý
- Laboratory of Plant Molecular Biology, Mendel University in Brno, Zemědělská 1, CZ-61300 Brno and Institute of Biophysics AS CR, v.v.i., Královopolská 135, CZ-61265 Brno, Czech Republic
| | - Filip Dyčka
- Institute of Analytical Chemistry AS CR, v.v.i., Veveří 97, CZ-60200 Brno, Czech Republic
| | - Janette Bobál'ová
- Institute of Analytical Chemistry AS CR, v.v.i., Veveří 97, CZ-60200 Brno, Czech Republic
| | - Břetislav Brzobohatý
- Laboratory of Plant Molecular Biology, Mendel University in Brno, Zemědělská 1, CZ-61300 Brno and Institute of Biophysics AS CR, v.v.i., Královopolská 135, CZ-61265 Brno, Czech Republic
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Kuderová A, Urbánková I, Válková M, Malbeck J, Brzobohaty B, Némethová D, Hejátko J. Effects of conditional IPT-dependent cytokinin overproduction on root architecture of Arabidopsis seedlings. PLANT & CELL PHYSIOLOGY 2008; 49:570-582. [PMID: 18296451 DOI: 10.1093/pcp/pcn029] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
Cytokinin (CK) has been known to inhibit primary root elongation and suggested to act as an auxin antagonist in the regulation of lateral root (LR) formation. While the role of auxin in root development has been thoroughly studied, the detailed and overall description of CK effects on root system morphology, particularly that of developing lateral root primordia (LRPs), and hence its role in organogenesis is still in progress. Here we examine the effects of conditional endogenous CK overproduction on root architecture and consider its temporal aspect during the early development of Arabidopsis thaliana. We employed the pOp/LhGR system to induce ectopic ipt overexpression with a glucocorticoid dexamethasone at designated developmental points. The transient CaMV 35S>GR>ipt transactivation greatly enhanced levels of biologically active CKs of zeatin (Z)-type and identified a distinct developmental interval during which primary root elongation is susceptible to increases in endogenous CK production. Long-term CK overproduction inhibited primary root elongation by reducing quantitative parameters of primary root meristem, disturbed a characteristic graded distribution pattern of auxin response in LRPs and impaired their development. Our findings indicate the impact of perturbed endogenous CK on the regulation of asymmetric auxin distribution during LRP development and imply that there is cross-talk between auxin and CK during organogenesis in A. thaliana.
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Affiliation(s)
- Alena Kuderová
- Laboratory of Plant Molecular Physiology, Department of Functional Genomics and Proteomics, Institute of Experimental Biology, Masaryk University, Kamenice 5, CZ-62500 Brno, Czech Republic
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Metabolism of plant hormones cytokinins and their function in signaling, cell differentiation and plant development. ACTA ACUST UNITED AC 2008. [DOI: 10.1016/s1572-5995(08)80028-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
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Lochmanová G, Zdráhal Z, Konecná H, Koukalová S, Malbeck J, Soucek P, Válková M, Kiran NS, Brzobohaty B. Cytokinin-induced photomorphogenesis in dark-grown Arabidopsis: a proteomic analysis. JOURNAL OF EXPERIMENTAL BOTANY 2008; 59:3705-19. [PMID: 18775952 DOI: 10.1093/jxb/ern220] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/10/2023]
Abstract
High concentrations of cytokinins (CKs) in the cultivation medium can induce partial photomorphogenesis in dark-grown Arabidopsis seedlings. However, no significant increases in endogenous CK levels have been found in de-etiolated mutants, suggesting that either parallel pathways are involved in the light and CK responses, or changes in the sensitivity to CKs occur during photomorphogenesis. Here it is shown that even modest increases in endogenous CK levels induced by transgenic expression of the CK biosynthetic gene, ipt, can lead to many typical features of light-induced de-etiolation, including inhibition of hypocotyl elongation and partial cotyledon opening. In addition, significant changes in expression of 37 proteins (mostly related to chloroplast biogenesis, a major element of light-induced photomorphogenesis) were detected by image and mass spectrometric analysis of two-dimensionally separated proteins. The identified chloroplast proteins were all up-regulated in response to increased CKs, and more than half are up-regulated at the transcript level during light-induced photomorphogenesis according to previously published transcriptomic data. Four of the up-regulated chloroplast proteins identified here have also been shown to be up-regulated during light-induced photomorphogenesis in previous proteomic analyses. In contrast, all differentially regulated mitochondrial proteins (the second largest group of differentially expressed proteins) were down-regulated. Changes in the levels of several tubulins are consistent with the observed morphological alterations. Further, 10 out of the 37 differentially expressed proteins detected have not been linked to either photomorphogenesis or CK action in light-grown Arabidopsis seedlings in previously published transcriptomic or proteomic analyses.
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Affiliation(s)
- Gabriela Lochmanová
- Institute of Biophysics AS CR, v.v.i., Královopolská 135, CZ-61265, Brno, Czech Republic
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Release of cotyledonary shoots of pea (Pisum sativum) seedlings from inhibition as related to endogenous zeatin and ethylene and exogenous IAA and benzyladenine. Biologia (Bratisl) 2007. [DOI: 10.2478/s11756-007-0002-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Zhang J, Wrage EL, Vankova R, Malbeck J, Neff MM. Over-expression of SOB5 suggests the involvement of a novel plant protein in cytokinin-mediated development. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2006; 46:834-48. [PMID: 16709198 DOI: 10.1111/j.1365-313x.2006.02745.x] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/09/2023]
Abstract
Cytokinins are a class of phytohormones that play a critical role in plant growth and development. sob5-D, an activation-tagging mutant, shows phenotypes typical of transgenic plants expressing the Agrobacterium tumefaciens isopentenyltransferase (ipt) gene that encodes the enzyme catalyzing the first step of cytokinin biosynthesis. The sob5-D mutant phenotypes are caused by over-expression of a novel gene, SOB5. Sequence analysis places SOB5 in a previously uncharacterized family of plant-specific proteins. A translational fusion between SOB5 and the green fluorescent protein reporter was localized in the cytoplasm as well as associated with the plasma membrane when transiently expressed in onion epidermal cells. Analysis of transgenic plants harboring an SOB5:SOB5-beta-glucuronidase (GUS) translational fusion under the control of the SOB5 promoter region showed GUS activity in vegetative tissues (hydathodes and trichomes of leaves, shoot meristems and roots) as well as in floral tissues (pistil tips, developing anthers and sepal vasculature). Cytokinin quantification analysis revealed that adult sob5-D plants accumulated higher levels of trans-zeatin riboside, trans-zeatin riboside monophosphate and isopentenyladenine 9-glucoside when compared to the wild-type. Consistent with this result, AtIPT3 and AtIPT7 were found to be up-regulated in a tissue-specific manner in sob5-D mutants. Physiological analysis of the sob5-D mutant demonstrated reduced responsiveness to exogenous cytokinin in both root-elongation and callus-formation assays. Taken together, our data suggest a role for the novel gene SOB5 in cytokinin-mediated plant development.
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Affiliation(s)
- Jingyu Zhang
- Department of Biology, Washington University, Campus Box 1137, One Brookings Drive, St Louis, MO 63130, USA
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Nováková M, Motyka V, Dobrev PI, Malbeck J, Gaudinová A, Vanková R. Diurnal variation of cytokinin, auxin and abscisic acid levels in tobacco leaves. JOURNAL OF EXPERIMENTAL BOTANY 2005; 56:2877-83. [PMID: 16157652 DOI: 10.1093/jxb/eri282] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
As many processes are regulated by both light and plant hormones, evaluation of diurnal variations of their levels may contribute to the elucidation of the complex network of light and hormone signal transduction pathways. Diurnal variation of cytokinin, auxin, and abscisic acid levels was tested in tobacco leaves (Nicotiana tabacum L. cv. Wisconsin 38) grown under a 16/8 h photoperiod. The main peak of physiologically active cytokinins (cytokinin bases and ribosides) was found after 9 h of light, i.e. 1 h after the middle of the light period. This peak coincided with the major auxin peak and was closely followed by a minor peak of abscisic acid. Free abscisic acid started to increase at the light/dark transition and reached its maximum 3 h after dark initiation. The content of total cytokinins (mainly N-glucosides, followed by cis-zeatin derivatives and nucleotides) exhibited the main peak after 9 h of light and the minor peak after the transition to darkness. The main, midday peak of active cytokinins was preceded by a period of minimal metabolic conversion of tritiated trans-zeatin (less than 30%). The major cytokinin-degrading enzyme, cytokinin oxidase/dehydrogenase (EC 1.5.99.12), exhibited maximal activity after the dark/light transition and during the diminishing of the midday cytokinin peak. The former peak might be connected with the elimination of the long-distance cytokinin signal. These cytokinin oxidase/dehydrogenase peaks were accompanied by increased activity of beta-glucosidase (EC 3.2.1.21), which might be involved in the hydrolysis of cytokinin O-glucosides and/or in fine-tuning of active cytokinin levels at their midday peak. The achieved data indicate that cytokinin metabolism is tightly regulated by the circadian clock.
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Affiliation(s)
- Marie Nováková
- Institute of Experimental Botany AS CR, Rozvojova 135, 165 02 Prague 6, Czech Republic
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Baroux C, Blanvillain R, Betts H, Batoko H, Craft J, Martinez A, Gallois P, Moore I. Predictable activation of tissue-specific expression from a single gene locus using the pOp/LhG4 transactivation system in Arabidopsis. PLANT BIOTECHNOLOGY JOURNAL 2005; 3:91-101. [PMID: 17168902 DOI: 10.1111/j.1467-7652.2004.00104.x] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/13/2023]
Abstract
The pOp/LhG4 transcription factor system was used to determine whether the synthetic pOp promoter, integrated at one position in the Arabidopsis genome, could be efficiently and faithfully activated by the heterologous transcription factor, LhG4, expressed in a variety of different patterns. This is a precondition for the development and exploitation of large collections of LhG4 activation lines that direct predictable tissue-specific expression of transgenes. We selected a pOp-GUS reporter insertion that was efficiently activated after crossing to an activator line that expressed the synthetic transcription factor LhG4 from the Cauliflower Mosaic Virus 35S promoter. This reporter line, pOp-GUS(g2), was then combined with activator loci that expressed LhG4 from one of seven different promoters, each with a different tissue specificity. pOp-GUS(g2) was activated faithfully in combination with six of these seven activator constructs, but generated an unexpected expression pattern in combination with the seventh construct, a fusion to a cyclin promoter (CYC-LhG4). The aberrant expression pattern could be attributed to the pOp-GUS(g2) insertion site, as the CYC-LhG4 activator lines directed the expected pattern of expression from a second pOp-GUS insertion. These results show that it is feasible to construct an activator collection in which LhG4 is expressed from diverse promoters or enhancer traps, but that individual pOp reporter loci can vary in their competence to respond to certain activator patterns. We discuss the implications for the design and use of mis-expression technology in Arabidopsis.
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Affiliation(s)
- Célia Baroux
- Laboratoire de Génome et Développement des Plantes, Université de Perpignan, 52 avenue de Villeneuve, 66860 Perpignan Cedex, France.
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Blagoeva E, Dobrev PI, Malbeck J, Motyka V, Strnad M, Hanus J, Vanková R. Cytokinin N-glucosylation inhibitors suppress deactivation of exogenous cytokinins in radish, but their effect on active endogenous cytokinins is counteracted by other regulatory mechanisms. PHYSIOLOGIA PLANTARUM 2004; 121:215-222. [PMID: 15153188 DOI: 10.1111/j.1399-3054.2004.00320.x] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
The prolongation of the effect of exogenous cytokinins by inhibition of their inactivation was studied in Raphanus sativus L. cv. Rampouch. As in radish the main way of cytokinin inactivation is their N-glucosylation, inhibitors of this pathway, papaverine, theophylline and olomoucine, as well as two olomoucine analogues, bohemine and roscovitine, were tested. The latter ones, which function as potent inhibitors of cyclin-dependent kinases, have also been found to effectively inhibit cytokinin N-glucosylation. Incubation (24 h) of de-rooted radish seedlings with inhibitors resulted in c. 50% decrease of the conversion of model cytokinins, [(3)H]dihydrozeatin and [(3)H]N(6)-benzyladenine, to the corresponding 7N-glucosides. Simultaneously the level of the non-metabolized cytokinin bases was elevated. The activity of cytokinin oxidase/dehydrogenase (EC 1.5.99.12) was suppressed in a dose dependent manner. The concentration of physiologically active endogenous cytokinins was not increased significantly by inhibitor application. The inhibition of N-glucosylation was in the case of olomoucine, bohemine and roscovitine accompanied by the accumulation of physiologically nonactive cis-zeatin derivatives. The impact of inhibitors on the endogenous cytokinin pool seems to be balanced by the mechanisms involved in the maintenance of cytokinin homeostasis.
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Affiliation(s)
- Elitsa Blagoeva
- Laboratory of Hormonal Regulations in Plants, Institute of Experimental Botany AS CR, Rozvojová 135, CZ-16502 Prague 6, Czech Republic
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