| 1. |
- Antoniadi, Ioanna, et al.
(författare)
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Cell-Type-Specific Cytokinin Distribution within the Arabidopsis Primary Root Apex
- 2015
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Ingår i: Plant Cell. - : Oxford University Press (OUP). - 1040-4651 .- 1532-298X. ; 27, s. 1955-1967
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Tidskriftsartikel (refereegranskat)abstract
- Cytokinins (CKs) play a crucial role in many physiological and developmental processes at the levels of individual plant components (cells, tissues, and organs) and by coordinating activities across these parts. High-resolution measurements of intracellular CKs in different plant tissues can therefore provide insights into their metabolism and mode of action. Here, we applied fluorescence-activated cell sorting of green fluorescent protein (GFP)-marked cell types, combined with solid-phase microextraction and an ultra-high-sensitivity mass spectrometry (MS) method for analysis of CK biosynthesis and homeostasis at cellular resolution. This method was validated by series of control experiments, establishing that protoplast isolation and cell sorting procedures did not greatly alter endogenous CK levels. The MS-based method facilitated the quantification of all the well known CK isoprenoid metabolites in four different transgenic Arabidopsis thaliana lines expressing GFP in specific cell populations within the primary root apex. Our results revealed the presence of a CK gradient within the Arabidopsis root tip, with a concentration maximum in the lateral root cap, columella, columella initials, and quiescent center cells. This distribution, when compared with previously published auxin gradients, implies that the well known antagonistic interactions between the two hormone groups are cell type specific.
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| 2. |
- Dolezal, Karel, et al.
(författare)
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An Intrinsic MicroRNA Timer Regulates Progressive Decline in Shoot Regenerative Capacity in Plants
- 2015
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Ingår i: Plant Cell. - : Oxford University Press (OUP). - 1040-4651 .- 1532-298X. ; 27, s. 349-360
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Tidskriftsartikel (refereegranskat)abstract
- Plant cells are totipotent and competent to regenerate from differentiated organs. It has been shown that two phytohormones, auxin and cytokinin, play critical roles within this process. As in animals, the regenerative capacity declines with age in plants, but the molecular basis for this phenomenon remains elusive. Here, we demonstrate that an age-regulated microRNA, miR156, regulates shoot regenerative capacity. As a plant ages, the gradual increase in miR156-targeted SQUAMOSA PROMOTER BINDING PROTEIN-LIKE (SPL) transcription factors leads to the progressive decline in shoot regenerative capacity. In old plants, SPL reduces shoot regenerative capacity by attenuating the cytokinin response through binding with the B-type ARABIDOPSIS RESPONSE REGULATORs, which encode the transcriptional activators in the cytokinin signaling pathway. Consistently, the increased amount of exogenous cytokinin complements the reduced shoot regenerative capacity in old plants. Therefore, the recruitment of age cues in response to cytokinin contributes to shoot regenerative competence.
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| 3. |
- Jones, Brian, et al.
(författare)
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Cytokinin regulation of auxin synthesis in Arabidopsis involves a homeostatic feedback loop regulated via auxin and cytokinin signal transduction.
- 2010
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Ingår i: The Plant Cell. - : American Society of Plant Biologists. - 1040-4651 .- 1532-298X. ; 22:9, s. 2956-2969
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Tidskriftsartikel (refereegranskat)abstract
- Together, auxin and cytokinin regulate many of the processes that are critical to plant growth, development, and environmental responsiveness. We have previously shown that exogenous auxin regulates cytokinin biosynthesis in Arabidopsis thaliana. In this work, we show that, conversely, the application or induced ectopic biosynthesis of cytokinin leads to a rapid increase in auxin biosynthesis in young, developing root and shoot tissues. We also show that reducing endogenous cytokinin levels, either through the induction of CYTOKININ OXIDASE expression or the mutation of one or more of the cytokinin biosynthetic ISOPENTENYLTRANSFERASE genes leads to a reduction in auxin biosynthesis. Cytokinin modifies the abundance of transcripts for several putative auxin biosynthetic genes, suggesting a direct induction of auxin biosynthesis by cytokinin. Our data indicate that cytokinin is essential, not only to maintain basal levels of auxin biosynthesis in developing root and shoot tissues but also for the dynamic regulation of auxin biosynthesis in response to changing developmental or environmental conditions. In combination with our previous work, the data suggest that a homeostatic feedback regulatory loop involving both auxin and cytokinin signaling acts to maintain appropriate auxin and cytokinin concentrations in developing root and shoot tissues.
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| 4. |
- Kopel, Pavel, et al.
(författare)
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Ferromagnetic Properties of a Trinuclear Nickel(II) Complex with a Trithiocyanurate Bridge
- 2009
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Ingår i: European Journal of Inorganic Chemistry. - 1434-1948 .- 1099-0682. ; 2009:36, s. 5475-5482
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Tidskriftsartikel (refereegranskat)abstract
- A novel trinuclear nickel(II) complex with N,N,N',N'',N''-pentamethyldiethylenetriamine (pmdien) and a trithiocyanurate(3-) (ttc3-) bridge of composition [Ni3(pmdien)3(μ-ttc)](ClO4)3 (1) was prepared. The X-ray crystal structure of 1 was determined, revealing the tris-N,S chelating mode of the trithiocyanurate bridge, forming a regular triangular NiII3 core. A deformed trigonal bipyramidal arrangement of the central atoms was further achieved by coordination of three pmdien N atoms. The complex shows a ferromagnetic exchange interaction among the NiII magnetic centers that is tuned by single-ion anisotropy and/or antisymmetric exchange. The complex orders ferromagnetically at Tc = 10 K and exhibits spin-glass properties.
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| 5. |
- Kopel, Pavel, et al.
(författare)
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Synthesis, characterization and screening of biological activity of Zn(II), Fe(II) and Mn(II) complexes with trithiocyanuric acid
- 2007
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Ingår i: Polyhedron. - : Elsevier BV. - 0277-5387. ; 26:8, s. 1583-1589
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Tidskriftsartikel (refereegranskat)abstract
- New Zn(II), Fe(II) and Mn(II) complexes with a combination of nitrogen-donor ligands and trithiocyanuric acid (ttcH3) were preparedand characterized by elemental analysis, IR and UV–Vis spectroscopies. The antitumor activity of the prepared complexes, together with already known Ni(II) species, were assayed in vitro against G-361 (human malignant melanoma), HOS (human osteogenic sarcoma), K-562 (human chronic myelogenous leukaemia) and MCF-7 (human breast adenocarcinoma) tumor cell lines. The IC50 values of the Fe(II) and Mn(II) compounds turned out to be lower than those of cisplatin and oxaliplatin. The antimicrobial activities were evaluated by MIC against bacteria (Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus and Enterococcus faecalis). Themolecular structure of [Zn(taa)(ttcH)].H2O (taa = tris(2-aminoethyl)amine) was determined by X-ray diffraction. The central atom is pentacoordinated by four N atoms of taa and one N atom of the ttcH dianion.
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| 6. |
- Kopel, Pavel, et al.
(författare)
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Trithiocyanurate Complexes of Iron, Manganese and Nickel and Their Anticholinesterase Activity
- 2014
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Ingår i: Molecules. - : MDPI AG. - 1420-3049 .- 1420-3049. ; 19:4, s. 4338-4354
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Tidskriftsartikel (refereegranskat)abstract
- The complexes of Fe(II), Mn(II) and Ni(II) with a combination of a Schiff base, nitrogen-donor ligand or macrocyclic ligand and trithiocyanuric acid (ttcH(3)) were prepared and characterized by elemental analysis and spectroscopies. Crystal and molecular structures of the iron complex of composition [Fe(L-1)](ttcH(2))(ClO4)center dot EtOH center dot H2O (1), where L-1 is Schiff base derived from tris(2-aminoethyl)amine and 2-pyridinecarboxaldehyde, were solved. It was found that the Schiff base is coordinated to the central iron atom by six nitrogens forming deformed octahedral arrangement, whereas trithiocyanurate(1-) anion, perchlorate and solvent molecules are not coordinated. The X-ray structure of the Schiff base sodium salt is also presented and compared with the iron complex. The anticholinesterase activity of the complexes was also studied.
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| 7. |
- Ljung, Karin, et al.
(författare)
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Hormonal control of the shoot stem-cell niche
- 2010
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 465, s. 1089-U154
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Tidskriftsartikel (refereegranskat)abstract
- The classic phytohormones cytokinin and auxin play essential roles in the maintenance of stem-cell systems embedded in shoot and root meristems, and exhibit complex functional interactions(1-4). Here we show that the activity of both hormones directly converges on the promoters of two A-type ARABIDOPSIS RESPONSE REGULATOR (ARR) genes, ARR7 and ARR15, which are negative regulators of cytokinin signalling(5) and have important meristematic functions(3). Whereas ARR7 and ARR15 expression in the shoot apical meristem (SAM) is induced by cytokinin, auxin has a negative effect, which is, at least in part, mediated by the AUXIN RESPONSE FACTOR5/MONOPTEROS (MP) transcription factor(6). Our results provide a mechanistic framework for hormonal control of the apical stem-cell niche and demonstrate how root and shoot stem-cell systems differ in their response to phytohormones.
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| 8. |
- Nordström, Anders, et al.
(författare)
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Auxin regulation of cytokinin biosynthesis in Arabidopsis thaliana : a factor of potential importance for auxin-cytokinin-regulated development.
- 2004
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 101:21, s. 8039-44
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Tidskriftsartikel (refereegranskat)abstract
- One of the most long-lived models in plant science is the belief that the long-distance transport and ratio of two plant hormones, auxin and cytokinin, at the site of action control major developmental events such as apical dominance. We have used in vivo deuterium labeling and mass spectrometry to investigate the dynamics of homeostatic cross talk between the two plant hormones. Interestingly, auxin mediates a very rapid negative control of the cytokinin pool by mainly suppressing the biosynthesis via the isopentenyladenosine-5'-monophosphate-independent pathway. In contrast, the effect of cytokinin overproduction on the entire auxin pool in the plant was slower, indicating that this most likely is mediated through altered development. In addition, we were able to confirm that the lateral root meristems are likely to be the main sites of isopentenyladenosine-5'-monophosphate-dependent cytokinin synthesis, and that the aerial tissue of the plant surprisingly also was a significant source of cytokinin biosynthesis. Our demonstration of shoot-localized synthesis, together with data demonstrating that auxin imposes a very rapid regulation of cytokinin biosynthesis, illustrates that the two hormones can interact also on the metabolic level in controlling plant development, and that the aerial part of the plant has the capacity to synthesize its own cytokinin independent of long-range transport from the root system.
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| 9. |
- Nordström, Anders, et al.
(författare)
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Derivatization for LC-electrospray ionization-MS : a tool for improving reversed-phase separation and ESI responses of bases, ribosides, and intact nucleotides.
- 2004
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Ingår i: Analytical Chemistry. - : American Chemical Society (ACS). - 0003-2700 .- 1520-6882. ; 76:10, s. 2869-77
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Tidskriftsartikel (refereegranskat)abstract
- We have developed a method for analyzing polar compounds by reversed-phase LC-ESI-MS following esterification of the analytes' free hydroxyl groups with propionyl or benzoyl acid anhydride. The method was applied to members of the plant hormone group cytokinins, which includes adenine bases, ribosides/glycosides, and nucleotides substituted at N-6 with an isoprenoid side chain, spanning a wide range of polarity. It was also used to analyze other compounds of biological importance, e.g., the nucleotides AMP, ADP, and ATP. The formation of more hydrophobic derivatives had a significant impact on two aspects of the analysis. The retention on a reversed-phase material was greatly increased without the use of any acetate/formate buffer or ion pairing reagent, and the ESI response was enhanced, due to the higher surface activities of the derivatives. Detection limits of propionylated cytokinins were in the high-attomole to low-femtomole range, an improvement by factors of 10-100 compared to previously reported figures. Using an automated SPE-based purification method, 12 endogenous cytokinins were quantified in extracts from 20- to 100-mg samples of leaves (from the plant Arabidopsis thaliana) with high accuracy and precision. Furthermore, the chromatographic properties of the benzoylated AMP, ADP, and ATP in the reversed-phase LC-MS system were much better in terms of retention, separation, and sensitivity than those of their underivatized counterparts, even without the use of any ion pairing reagent. Our data show that derivatization followed by LC-ESI-MS is an effective strategy for analyzing low molecular weight compounds, enabling compounds with a wide range of polarity to be determined in a single-injection LC-MS analysis.
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| 10. |
- Parizkova, Barbora, et al.
(författare)
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iP & OEIP - Cytokinin Micro Application Modulates Root Development with High Spatial Resolution
- 2022
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Ingår i: Advanced Materials Technologies. - : Wiley. - 2365-709X. ; 7:10
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Tidskriftsartikel (refereegranskat)abstract
- State-of-the-art technology based on organic electronics can be used as a flow-free delivery method for organic substances with high spatial resolution. Such highly targeted drug micro applications can be used in plant research for the regulation of physiological processes on tissue and cellular levels. Here, for the first time, an organic electronic ion pump (OEIP) is reported that can transport an isoprenoid-type cytokinin, N-6-isopentenyladenine (iP), to intact plants. Cytokinins (CKs) are plant hormones involved in many essential physiological processes, including primary root (PR) and lateral root (LR) development. Using the Arabidopsis thaliana root as a model system, efficient iP delivery is demonstrated with a biological output - cytokinin-related PR and LR growth inhibition. The spatial resolution of iP delivery, defined for the first time for an organic compound, is shown to be less than 1 mm, exclusively affecting the OEIP-targeted LR. Results from the application of the high-resolution OIEP treatment method confirm previously published findings showing that the influence of CKs may vary at different stages of LR development. Thus, OEIP-based technologies offer a novel, electronically controlled method for phytohormone delivery that could contribute to unraveling cytokinin functions during different developmental processes with high specificity.
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