Cytokinins and their sugar or non-sugar conjugates are very active growth-promoting factors in plants, although they occur at very low concentrations. These compounds have been identified in numerous plant species. This review predominantly focuses on 9-substituted adenine-based cytokinin conjugates, both artificial and endogenous, sugar and non-sugar, and their roles in plants. Acquired information about their biological activities, interconversions, and metabolism improves understanding of their mechanisms of action and functions in planta. Although a number of 9-substituted cytokinins occur endogenously, many have also been prepared in laboratories to facilitate the clarification of their physiological roles and the determination of their biological properties. Here, we chart advances in knowledge of 9-substituted cytokinin conjugates from their discovery to current understanding and reciprocal interactions between biological properties and associated structural motifs. Current organic chemistry enables preparation of derivatives with better biological properties, such as improved anti-senescence, strong cell division stimulation, shoot forming, or more persistent stress tolerance compared to endogenous or canonical cytokinins. Many artificial cytokinin conjugates stimulate higher mass production than naturally occurring cytokinins, improve rooting, or simply have high stability or bioavailability. Thus, knowledge of the biosynthesis, metabolism, and activity of 9-substituted cytokinins in various plant species extends the scope for exploiting both natural and artificially prepared cytokinins in plant biotechnology, tissue culture, and agriculture.

• Klíčová slova
• D-arabinoside, cytokinin nucleosides, cytokinin sugar conjugates, disaccharides, glucoside, meta-topolin, plant biotechnology, plant tissue culture, riboside, zeatin,
• MeSH
• adenin chemie   metabolismus   MeSH
• cytokininy biosyntéza   chemie   metabolismus   MeSH
• molekulární struktura MeSH
• rostliny chemie   metabolismus   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• přehledy MeSH
• Názvy látek
• adenin MeSH
• cytokininy MeSH

Cytokinins are plant hormones with biological functions ranging from coordination of plant growth and development to the regulation of senescence. A series of 2-chloro-N(6)-(halogenobenzylamino)purine ribosides was prepared and tested for cytokinin activity in detached wheat leaf senescence, tobacco callus and Amaranthus bioassays. The synthetic compounds showed significant activity, especially in delaying senescence in detached wheat leaves. They were also tested in bacterial receptor bioassays using both monocot and dicot members of the cytokinin receptor family. Most of the derivatives did not trigger cytokinin signaling via the AHK3 and AHK4 receptors from Arabidopsis thaliana in the bacterial assay, but some of them specifically activated the ZmHK1 receptor from Zea mays and were also more active than the aromatic cytokinin BAP in an ARR5::GUS cytokinin bioassay using transgenic Arabidopsis plants. Whole transcript expression analysis was performed using an Arabidopsis model to gather information about the reprogramming of gene transcription when senescent leaves were treated with selected C2-substituted aromatic cytokinin ribosides. Genome-wide expression profiling revealed that the synthetic halogenated derivatives induced the expression of genes related to cytokinin signaling and metabolism. They also prompted both up- and down-regulation of a unique combination of genes coding for components of the photosystem II (PSII) reaction center, light-harvesting complex II (LHCII), and the oxygen-evolving complex, as well as several stress factors responsible for regulating photosynthesis and chlorophyll degradation. Chlorophyll content and fluorescence analyses demonstrated that treatment with the halogenated derivatives increased the efficiency of PSII photochemistry and the abundance of LHCII relative to DMSO- and BAP-treated controls. These findings demonstrate that it is possible to manipulate and fine-tune leaf longevity using synthetic aromatic cytokinin analogs.

• Klíčová slova
• Aromatic cytokinin, Cytokinin activity, Gene expression, Photosynthesis, Photosystem, Ribosides, Senescence delay, Synthesis,
• MeSH
• amarant metabolismus   MeSH
• Arabidopsis metabolismus   MeSH
• cytokininy metabolismus   MeSH
• fotosyntetická reakční centra (proteinové komplexy) fyziologie   MeSH
• listy rostlin metabolismus   MeSH
• metabolismus sacharidů fyziologie   MeSH
• pšenice metabolismus   MeSH
• purinové nukleosidy chemická syntéza   chemie   MeSH
• ribonukleosidy chemická syntéza   chemie   MeSH
• stárnutí účinky léků   fyziologie   MeSH
• tabák metabolismus   MeSH
• vývoj rostlin účinky léků   MeSH
• vztahy mezi strukturou a aktivitou MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• cytokininy MeSH
• fotosyntetická reakční centra (proteinové komplexy) MeSH
• nebularine MeSH Prohlížeč
• purinové nukleosidy MeSH
• ribonukleosidy MeSH

We characterized the molecular function of the Pseudomonas syringae pv. tomato DC3000 (Pto) effector HopQ1. In silico studies suggest that HopQ1 might possess nucleoside hydrolase activity based on the presence of a characteristic aspartate motif. Transgenic Arabidopsis lines expressing HopQ1 or HopQ1 aspartate mutant variants were characterized with respect to flagellin triggered immunity, phenotype and changes in phytohormone content by high-performance liquid chromatography-MS (HPLC-MS). We found that HopQ1, but not its aspartate mutants, suppressed all tested immunity marker assays. Suppression of immunity was the result of a lack of the flagellin receptor FLS2, whose gene expression was abolished by HopQ1 in a promoter-dependent manner. Furthermore, HopQ1 induced cytokinin signaling in Arabidopsis and the elevation in cytokinin signaling appears to be responsible for the attenuation of FLS2 expression. We conclude that HopQ1 can activate cytokinin signaling and that moderate activation of cytokinin signaling leads to suppression of FLS2 accumulation and thus defense signaling.

• Klíčová slova
• FLS2, HopQ1, cytokinin, flagellin, innate immunity, type III effector,
• MeSH
• Arabidopsis účinky léků   imunologie   fyziologie   MeSH
• bakteriální proteiny genetika   fyziologie   MeSH
• cytokininy metabolismus   farmakologie   MeSH
• geneticky modifikované rostliny metabolismus   MeSH
• odolnost vůči nemocem * MeSH
• proteinkinasy metabolismus   MeSH
• proteiny huseníčku metabolismus   MeSH
• Pseudomonas syringae genetika   fyziologie   MeSH
• regulátory růstu rostlin metabolismus   MeSH
• signální transdukce MeSH
• vysokoúčinná kapalinová chromatografie MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• bakteriální proteiny MeSH
• cytokininy MeSH
• FLS2 protein, Arabidopsis MeSH Prohlížeč
• proteinkinasy MeSH
• proteiny huseníčku MeSH
• regulátory růstu rostlin MeSH

We present a comprehensive characterization of the nucleoside N-ribohydrolase (NRH) family in two model plants, Physcomitrella patens (PpNRH) and maize (Zea mays; ZmNRH), using in vitro and in planta approaches. We identified two NRH subclasses in the plant kingdom; one preferentially targets the purine ribosides inosine and xanthosine, while the other is more active toward uridine and xanthosine. Both subclasses can hydrolyze plant hormones such as cytokinin ribosides. We also solved the crystal structures of two purine NRHs, PpNRH1 and ZmNRH3. Structural analyses, site-directed mutagenesis experiments, and phylogenetic studies were conducted to identify the residues responsible for the observed differences in substrate specificity between the NRH isoforms. The presence of a tyrosine at position 249 (PpNRH1 numbering) confers high hydrolase activity for purine ribosides, while an aspartate residue in this position confers high activity for uridine. Bud formation is delayed by knocking out single NRH genes in P. patens, and under conditions of nitrogen shortage, PpNRH1-deficient plants cannot salvage adenosine-bound nitrogen. All PpNRH knockout plants display elevated levels of certain purine and pyrimidine ribosides and cytokinins that reflect the substrate preferences of the knocked out enzymes. NRH enzymes thus have functions in cytokinin conversion and activation as well as in purine and pyrimidine metabolism.

• MeSH
• biokatalýza * účinky léků   MeSH
• cytokininy chemie   metabolismus   MeSH
• dusík farmakologie   MeSH
• fenotyp MeSH
• fylogeneze MeSH
• genový knockout MeSH
• hydrolýza účinky léků   MeSH
• kinetika MeSH
• krystalografie rentgenová MeSH
• kukuřice setá účinky léků   enzymologie   genetika   MeSH
• mechy účinky léků   enzymologie   genetika   růst a vývoj   MeSH
• molekulární modely MeSH
• molekulární sekvence - údaje MeSH
• mutageneze cílená MeSH
• mutantní proteiny chemie   metabolismus   MeSH
• N-glykosylhydrolasy chemie   genetika   metabolismus   MeSH
• pyrimidiny chemie   metabolismus   MeSH
• ribonukleosidy chemie   metabolismus   MeSH
• sekvence aminokyselin MeSH
• sekvenční seřazení MeSH
• substrátová specifita účinky léků   MeSH
• vazebná místa MeSH
• vztahy mezi strukturou a aktivitou MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• cytokininy MeSH
• dusík MeSH
• mutantní proteiny MeSH
• N-glykosylhydrolasy MeSH
• pyrimidine MeSH Prohlížeč
• pyrimidiny MeSH
• ribonukleosidy MeSH

Cells save their energy during nitrogen starvation by selective autophagy of ribosomes and degradation of RNA to ribonucleotides and nucleosides. Nucleosides are hydrolyzed by nucleoside N-ribohydrolases (nucleosidases, NRHs). Subclass I of NRHs preferentially hydrolyzes the purine ribosides while subclass II is more active towards uridine and xanthosine. Here, we performed a crystallographic and kinetic study to shed light on nucleoside preferences among plant NRHs followed by in vivo metabolomic and phenotyping analyses to reveal the consequences of enhanced nucleoside breakdown. We report the crystal structure of Zea mays NRH2b (subclass II) and NRH3 (subclass I) in complexes with the substrate analog forodesine. Purine and pyrimidine catabolism are inseparable because nucleobase binding in the active site of ZmNRH is mediated via a water network and is thus unspecific. Dexamethasone-inducible ZmNRH overexpressor lines of Arabidopsis thaliana, as well as double nrh knockout lines of moss Physcomitrium patents, reveal a fine control of adenosine in contrast to other ribosides. ZmNRH overexpressor lines display an accelerated early vegetative phase including faster root and rosette growth upon nitrogen starvation or osmotic stress. Moreover, the lines enter the bolting and flowering phase much earlier. We observe changes in the pathways related to nitrogen-containing compounds such as β-alanine and several polyamines, which allow plants to reprogram their metabolism to escape stress. Taken together, crop plant breeding targeting enhanced NRH-mediated nitrogen recycling could therefore be a strategy to enhance plant growth tolerance and productivity under adverse growth conditions.

• Klíčová slova
• Physcomitrella patens, Zea mays, crystal structure, cytokinin, nitrogen starvation, nucleoside N-ribohydrolase, overexpression, polyamine, purine,
• MeSH
• Arabidopsis * genetika   MeSH
• dusík metabolismus   MeSH
• nukleosidy * metabolismus   MeSH
• rostliny metabolismus   MeSH
• šlechtění rostlin MeSH
• uridin metabolismus   MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• dusík MeSH
• nukleosidy * MeSH
• uridin MeSH

Cytokinins are a class of phytohormones, signalling molecules specific to plants. They act as regulators of diverse physiological processes in complex signalling pathways. It is necessary for plants to continuously regulate cytokinin distribution among different organs, tissues, cells, and compartments. Such regulatory mechanisms include cytokinin biosynthesis, metabolic conversions and degradation, as well as cytokinin membrane transport. In our review, we aim to provide a thorough picture of the latter. We begin by summarizing cytokinin structures and physicochemical properties. Then, we revise the elementary thermodynamic and kinetic aspects of cytokinin membrane transport. Next, we review which membrane-bound carrier proteins and protein families recognize cytokinins as their substrates. Namely, we discuss the families of "equilibrative nucleoside transporters" and "purine permeases", which translocate diverse purine-related compounds, and proteins AtPUP14, AtABCG14, AtAZG1, and AtAZG2, which are specific to cytokinins. We also address long-distance cytokinin transport. Putting all these pieces together, we finally discuss cytokinin distribution as a net result of these processes, diverse in their physicochemical nature but acting together to promote plant fitness.

• Klíčová slova
• ABCG14, AZG1, AZG2, PUP14, cytokinin distribution, cytokinin hydrophobicity, cytokinin transport, membrane transport,
• MeSH
• Arabidopsis metabolismus   MeSH
• biologický transport MeSH
• buněčná membrána metabolismus   MeSH
• cytokininy metabolismus   MeSH
• homeostáza MeSH
• hydrofobní a hydrofilní interakce MeSH
• kinetika MeSH
• kořeny rostlin metabolismus   MeSH
• membránové transportní proteiny metabolismus   MeSH
• proteiny huseníčku genetika   MeSH
• regulace genové exprese u rostlin MeSH
• regulátory růstu rostlin metabolismus   MeSH
• signální transdukce fyziologie   MeSH
• termodynamika MeSH
• výhonky rostlin metabolismus   MeSH
• Publikační typ
• časopisecké články MeSH
• přehledy MeSH
• Názvy látek
• cytokininy MeSH
• membránové transportní proteiny MeSH
• proteiny huseníčku MeSH
• regulátory růstu rostlin MeSH

Drought and salinity reduce seed germination, seedling emergence, and early seedling establishment, affect plant metabolism, and hence, reduce crop yield. Development of technologies that can increase plant tolerance of these challenging growth conditions is a major current interest among plant scientists and breeders. Seed priming has become established as one of the practical approaches that can alleviate the negative impact of many environmental stresses and improve the germination and overall performance of crops. Hormopriming using different plant growth regulators has been widely demonstrated as effective, but information about using cytokinins (CKs) as priming agents is limited to only a few studies using kinetin or 6-benzylaminopurine (BAP). Moreover, the mode of action of these compounds in improving seed and plant fitness through priming has not yet been studied. For many years, BAP has been one of the CKs most commonly applied exogenously to plants to delay senescence and reduce the impact of stress. However, rapid endogenous N 9-glucosylation of BAP can result in negative effects. This can be suppressed by hydroxylation of the benzyl ring or by appropriate N 9 purine substitution. Replacement of the 2' or 3' hydroxyl groups of a nucleoside with a fluorine atom has shown promising results in drug research and biochemistry as a means of enhancing biological activity and increasing chemical or metabolic stability. Here, we show that the application of this chemical modification in four new N 9-substituted CK derivatives with a fluorinated carbohydrate moiety improved the antisenescence properties of CKs. Besides, detailed phenotypical analysis of the growth and development of Arabidopsis plants primed with the new CK analogs over a broad concentration range and under various environmental conditions revealed that they improve growth regulation and antistress activity. Seed priming with, for example, 6-(3-hydroxybenzylamino)-2'-deoxy-2'-fluoro-9-(β)-D-arabinofuranosylpurine promoted plant growth under control conditions and alleviated the negative effects of the salt and osmotic stress. The mode of action of this hormopriming and its effect on plant metabolism were further analyzed through quantification of the endogenous levels of phytohormones such as CKs, auxins and abscisic acid, and the results are discussed.

• Klíčová slova
• Arabidopsis, abiotic stress, antisenescence, cytokinin analogs, hormopriming, plant biostimulant characterization index,
• Publikační typ
• časopisecké články MeSH

Expression systems based on high selectivity and activity of T7 RNA polymerase and presence of a strong T7 promoter have been commonly used for cloning and expression of various recombinant proteins in Escherichia coli. When the expression system is designed in such a way that the produced protein is not being transferred into periplasm, bacterial cells must be lysed in order to isolate and purify the protein. The final yield and quality of the synthesized protein then depend on various factors, protein size, amino acid sequence, solubility in cytoplasm, and folding requirements among them. The yield in the T7 RNA polymerase/promoter system can be positively influenced by use of rifampicin. In this report we demonstrate usefulness of the antibiotic in detail. We describe rifampicin-enhanced expression of a plant cytokinin-specific beta-glucosidase. Two bacterial cultures are compared, one expressing the enzyme without and one in the presence of rifampicin. The antibiotic not only increased the yield of the recombinant protein, which seems to be a general phenomenon, but also favored the final assembly of the protein's subunits into a catalytically active dimer form.

• MeSH
• beta-glukosidasa chemie   imunologie   metabolismus   MeSH
• cytokininy chemie   MeSH
• dimerizace MeSH
• DNA řízené RNA-polymerasy metabolismus   MeSH
• Escherichia coli enzymologie   MeSH
• konformace proteinů MeSH
• rekombinantní proteiny chemie   metabolismus   MeSH
• rifampin farmakologie   MeSH
• sbalování proteinů MeSH
• virové proteiny MeSH
• western blotting MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• bacteriophage T7 RNA polymerase MeSH Prohlížeč
• beta-glukosidasa MeSH
• cytokinin-beta-glucosidase MeSH Prohlížeč
• cytokininy MeSH
• DNA řízené RNA-polymerasy MeSH
• rekombinantní proteiny MeSH
• rifampin MeSH
• virové proteiny MeSH

Cytokinins are naturally occurring substances that act as plant growth regulators promoting plant growth and development, including shoot initiation and branching, and also affecting apical dominance and leaf senescence. Aromatic cytokinin 6-benzylaminopurine (BAP) has been widely used in micropropagation systems and biotechnology. However, its 9-glucoside (BAP9G) accumulates in explants, causing root inhibition and growth heterogenity. To overcome BAP disadvantages, a series of ring-substituted 2'-deoxy-9-(β)-d-ribofuranosylpurine derivatives was prepared and examined in different classical cytokinin bioassays. Amaranthus, senescence and tobacco callus bioassays were employed to provide details of cytokinin activity of 2'-deoxy-9-(β)-d-ribosides compared to their respective free bases and ribosides. The prepared derivatives were also tested for their recognition by cytokinin receptors of Arabidopsis thaliana AHK3 and CRE1/AHK4. The ability of aromatic N6-substituted adenine-2'-deoxy-9-(β)-d-ribosides to promote plant growth and delay senescence was increased considerably and, in contrast to BAP, no loss of cytokinin activity at higher concentrations was observed. The presence of a 2'-deoxyribosyl moiety at the N9-position led to an increase in cytokinin activities in comparison to the free bases and ribosides. The antioxidant capacity, cytotoxicity and effect on the MHV-68 gammaherpesvirus strain were also examined.

• Klíčová slova
• 2′-Deoxyribosides, Antioxidative capacity, Antiviral testing, Aromatic cytokinins, Plant growth regulator, Purine derivatives,
• MeSH
• antioxidancia chemická syntéza   chemie   farmakologie   MeSH
• Arabidopsis účinky léků   metabolismus   MeSH
• Cercopithecus aethiops MeSH
• molekulární struktura MeSH
• purinové nukleosidy chemická syntéza   chemie   farmakologie   MeSH
• regulátory růstu rostlin chemická syntéza   chemie   farmakologie   MeSH
• Vero buňky MeSH
• vztah mezi dávkou a účinkem léčiva MeSH
• vztahy mezi strukturou a aktivitou MeSH
• zvířata MeSH
• Check Tag
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• antioxidancia MeSH
• purinové nukleosidy MeSH
• regulátory růstu rostlin MeSH