Disease relevance of Zeatin

• This gene confers upon E. coli the ability to synthesize and secrete several cytokinins including trans-zeatin, iso-pentenyladenine and their respective N9-ribosyl derivatives [1].
• The nucleotide sequence of a Pseudomonas trans-zeatin producing gene (ptz) from the pCK1 plasmid of Pseudomonas syringae pv. savastanoi strain 1006 has been determined [1].
• Agrobacterium IPTs have the ability to produce tZ-type species directly by use of hydroxymethylbutenyl diphosphate as the side chain donor [2].
• Water stress substantially increased ABA but reduced zeatin (Z) + zeatin riboside (ZR) concentrations in the root exudates and leaves [3].
• tRNA is the source of low-level trans-zeatin production in Methylobacterium spp [4].

High impact information on Zeatin

• Crystal Structure of Vigna radiata Cytokinin-Specific Binding Protein in Complex with Zeatin [5].
• In addition, we have crystallized this cytokinin-specific binding protein (Vr CSBP) in complex with zeatin and refined the structure to 1.2 A resolution [5].
• Unlike in the conventional CK biosynthesis pathway in plants, trans-zeatin-type CKs are produced directly without the requirement for P450 monooxygenase-mediated hydroxylation [6].
• Double tracer analysis, using [(2)H(6)] isopentenyladenosine and deuterium oxide, provided evidence for an alternative, iPMP-independent, biosynthetic pathway for zeatin-type cytokinins, present in both ipt-expressing and wild-type Arabidopsis thaliana [7].
• UGT85A1, UGT73C5, and UGT73C1 recognized trans-zeatin and dihydrozeatin, which have an available hydroxyl group for glucosylation and formed the O-glucosides [8].

Chemical compound and disease context of Zeatin

• In the recombinant E. coli system, ZmHK1 and ZmHK3a were more sensitive to free-base cytokinins than to the corresponding nucleosides; isopentenyladenine was most effective for ZmHK1, while ZmHK2 tended to be most sensitive to trans-zeatin and the riboside [9].
• Secretion of trans-zeatin by Agrobacterium tumefaciens: a function determined by the nopaline Ti plasmid [10].

Biological context of Zeatin

• Out of eight different aminopurines and a synthetic auxin tested for their ability to override lovastatin inhibition of mitosis, only zeatin was active [11].
• As ectopic morphogenesis proceeded, HtKNOT1 transcripts and zeatin co-localized and showed different patterns in ectopic shoot compared with embryo-like structures, consistent with the differential role of both cytokinin and knox genes in the two morphogenetic events [12].
• Photosynthetic rate and zeatin + zeatin riboside concentrations in the flag leaves declined faster in WS plants than in WW plants, and they decreased more slowly with HN than with NN when soil water potential was the same, indicating that the water deficit enhanced, whereas HN delayed, senescence [13].
• In contrast, there were sharp peaks in the levels of specific cytokinins (zeatin- and dihydrozeatin-type) at the end of the S phase and during mitosis [14].
• The SE were obtained by a simple somatic embryogenesis protocol: leaf explants from two adult plants (QsG0, QsG5) and from two juvenile plants (QsGM1, QsGM2) were inoculated on Murashige and Skoog (MS) medium with 2,4-dichlorophenoxyacetic acid and zeatin [15].

Anatomical context of Zeatin

• Zeatin-binding protein (67 +/- 2 kDa) was isolated from the cytosol of the first leaf of 10-day-old barley plants [16].
• Overexpression of FPS in mitochondria also led to altered leaf cytokinin profile, with a reduction in the contents of physiologically active trans-zeatin- and isopentenyladenine-type cytokinins and their corresponding riboside monophosphates as well as enhanced levels of cis-zeatin 7-glucoside and storage cytokinin O-glucosides [17].
• The bacterium induces the formation of tumorous galls by the synthesis and secretion of the plant hormones trans-zeatin riboside and indole-3-acetic acid into host intercellular spaces [18].
• Gerontomodulatory and youth-preserving effects of zeatin on human skin fibroblasts undergoing aging in vitro [19].
• Inhibitory effect of zeatin, isolated from Fiatoua villosa, on acetylcholinesterase activity from PC12 cells [20].

Associations of Zeatin with other chemical compounds

• Cytokinins (CKs), a group of phytohormones, are adenine derivatives that carry either an isoprene-derived or an aromatic side chain at the N(6) terminus. trans-Zeatin (tZ), an isoprenoid CK, is assumed to play a central physiological role because of its general occurrence and high activity in bioassays [21].
• Indole-3-acetic acid (IAA) and combined zeatin riboside (ZR) and zeatin riboside-5'-monophosphate (ZRMP) contents were analysed by mass spectrometry in young, developing leaves from the cross, the parental lines and the wild type [22].
• O-Glucosylation is stereo-specific: the O-glucosyltransferase encoded by the Phaseolus lunatus ZOG1 gene has high affinity for trans-zeatin as the substrate, whereas the enzyme encoded by the maize (Zea mays) cisZOG1 gene prefers cis-zeatin [23].
• Using a zeatin affinity column a 40 kDa protein was isolated from tobacco Bright Yellow 2 (TBY-2) and identified by mass spectrometry as adenosine kinase [24].
• In high light (300 mumol PPFD m-2 s-1), ipt mRNA was detected and zeatin/zeatin glucoside levels were 10-fold higher than in control plants or when transformants were grown in low light (30 mumol PPFD m-2 s-1) [25].

Gene context of Zeatin

• Direct measurements demonstrate that AtPUP1 is capable of mediating uptake of radiolabeled trans-zeatin [26].
• In contrast to their high activity in bioassays, the BAP derivatives were recognised with much lower sensitivity than trans-zeatin in both Arabidopsis thaliana AHK3 and AHK4 receptor assays [27].
• Two enzymes catalyzing the formation of O-glycosyl derivatives of zeatin have been characterized, O-glucosyltransferase and O-xylosyltransferase, occurring in seeds of lima bean (Phaseolus lunatus) and bean (Phaseolus vulgaris), respectively [28].
• Tobacco chloroplasts from dark-treated leaves contained zeatin riboside-O-glucoside and dihydrozeatin riboside-O-glucoside, as well as a relatively high CK oxidase activity [29].
• In higher plants, trans-zeatin (tZ), a major CK, is formed by subsequent hydroxylation, which is catalyzed by a cytochrome P450 monooxygenase (P450), CYP735A1 or CYP735A2 [2].

Analytical, diagnostic and therapeutic context of Zeatin

• Using recombinant protein and isothermal titration calorimetry as well as fluorescence measurements coupled with ligand displacement, we have reexamined the K(d) values and show them to range from approximately 10(-6) M (for 4PU30) to 10(-4) M (for zeatin) for 1:1 stoichiometry complexes [5].
• Mutant exconjugants, confirmed by PCR, did not contain zeatin in their tRNAs and did not secrete zeatin into the medium, findings which are consistent with the hypothesis that all zeatin is tRNA derived rather than synthesized de novo [4].
• Using immunoaffinity and high-performance liquid chromatography (HPLC) purification, we obtained 22 to 111 ng of trans-zeatin per liter from culture filtrates of four PPFM leaf isolates (from Arabidopsis, barley, maize, and soybean) and of a Methylobacterium extorquens type culture originally recovered as a soil isolate [4].
• Embryos were analyzed by ELISA for abscisic acid (ABA), abscisic acid-glucose ester, 2,4-D, indole-3-acetic acid (IAA), indole-3-aspartate (IAAsp), zeatin (Z), zeatin riboside (ZR), isopentenyladenine (iP) and isopentenyladenosine (iPA) [30].
• Double-solvent extraction followed by fractionation with both normal and reverse phase column chromatographies and analysis by liquid chromatography/tandem mass spectrometry identified trans-zeatin riboside (ZR) as the primary suppressor of adventitious root formation [31].

References