High-performance liquid chromatography of cytokinins

Comparison of heterogeneous and homogeneous radioactivity flow detectors for simultaneous profiling and LC-MS/MS characterization of metabolites

Methods for simultaneous liquid chromatography-radioactivity monitor (LC-RAM) metabolite profiling and LC-tandem mass spectrometry (MS/MS) characterization of metabolites are described. Profiling and characterization of metabolites from three drug candidates from different therapeutic areas were compared using in-line heterogeneous LC-RAM-MS/MS and homogeneous LC-RAM-MS/MS methods. Although comparison shows that simultaneous metabolite profiling and characterization can be achieved using either heterogeneous or homogeneous-LC-RAM-MS/MS systems, a homogeneous system has the advantage in the following aspects, (1) sensitivity; (2) ease of method transfer; (3) less peak broadening problems due to the drug or metabolites adhering to the RAM cell; (4) accuracy in quantitation of the metabolites; and (5) the ability to load larger volumes of unprocessed biological fluids. Furthermore, the study shows that some of the possible metabolites that do not ionize well with electrospray ionization (ESI) and eluded detection by heterogeneous-LC-RAM detection could be very easily detected and characterized using a homogeneous-LC-RAM-MS/MS system.

Hormonal changes induced by partial rootzone drying of irrigated grapevine

Partial rootzone drying (PRD) is a new irrigation technique which improves the water use efficiency (by up to 50%) of wine grape production without significant crop reduction. The technique was developed on the basis of knowledge of the mechanisms controlling transpiration and requires that approximately half of the root system is always maintained in a dry or drying state while the remainder of the root system is irrigated. The wetted and dried sides of the root system are alternated on a 10-14 d cycle. Abscisic acid (ABA) concentration in the drying roots increases 10-fold, but ABA concentration in leaves of grapevines under PRD only increased by 60% compared with a fully irrigated control. Stomatal conductance of vines under PRD irrigation was significantly reduced when compared with vines receiving water to the entire root system. Grapevines from which water was withheld from the entire root system, on the other hand, show a similar reduction in stomatal conductance, but leaf ABA increased 5-fold compared with the fully irrigated control. PRD results in increased xylem sap ABA concentration and increased xylem sap pH, both of which are likely to result in a reduction in stomatal conductance. In addition, there was a reduction in zeatin and zeatin-riboside concentrations in roots, shoot tips and buds of 60, 50 and 70%, respectively, and this may contribute to the reduction in shoot growth and intensified apical dominance of vines under PRD irrigation. There is a nocturnal net flux of water from wetter roots to the roots in dry soil and this may assist in the distribution of chemical signals necessary to sustain the PRD effect. It was concluded that a major effect of PRD is the production of chemical signals in drying roots that are transported to the leaves where they bring about a reduction in stomatal conductance.

Study of cytokinin metabolism using HPLC with radioisotope detection

High performance liquid chromatography (HPLC) with an on-line flow-through radioactivity detector was used to monitor the metabolism of cytokinins ([3H]6-benzylaminopurine and [3H]6-benzylaminopurine riboside) after their incorporation into wheat seedlings. The production and conversion of individual metabolites was assayed within a short time interval (0.5-3 h). Extraction recoveries from plant tissue proved to be 85%. The uptake of both cytokinins was very rapid and differences in their metabolism were already perceptible after 30 min. The individual metabolites were identified as adenine (Ade), adenosine (Ado), benzyladenine-9-glucoside (BA-9G), 6-benzyladenine (BA) and benzyladenosine (BAR). The method is very fast, sensitive and very useful for metabolic studies. The detection limit was 40 pg (220 Bq) for BA at the level of 2 ng ml-1.

Immunoaffinity co-purification of cytokinins and analysis by high-performance liquid chromatography with ultraviolet-spectrum detection

A rapid methodology for the simultaneous analysis of a large number of cytokinins is presented. The cross-reactivity of a mixture of polyclonal antibodies against zeatin riboside and isopentenyladenosine was exploited in a protocol that can be used for immunoaffinity purification of 23 additional cytokinins. Ligands include the cytokinin bases zeatin, dihydrozeatin, isopentenyladenine, benzyl-adenine and kinetin, and their corresponding nucleoside, nucleoside-5'-monophosphate, and 9-glucoside derivatives, as well as cis-zeatin, cis-zeatin riboside, the 2-methylthiol derivatives of isopentenyladenosine and zeatin riboside, and benzyl-adenine-3-glucoside. Mixtures of cytokinins could be retained with high recoveries of all the components. Immunoaffinity purification of extracts of Arabidopsis thaliana (L.) Heynh. and Solarium tuberosum L. gave fractions clean enough, as verified by gas chromatographymass spectrometry (GC-MS), to allow analysis of endogenous cytokinins using a single high-performance liquid chromatography (HPLC) step with on-line UV-spectrum detection. The detection limit was 4-6 pmol. The procedure described forms a routine assaying technique that is faster and simpler, yet yields better qualitative and quantitative information than the commonly used procedure of immunoassaying of HPLC fractions.

Immunochemical identification of a tRNA-independent cytokinin-like compound in Salmonella typhimurium

Chemical and immunological characterization of Salmonella typhimurium cell extracts indicates that this organism produces a molecule which closely resembles the plant growth regulator, cytokinin. Alcohol-soluble cationic ultraviolet-absorbing material was fractionated by reverse-phase HPLC using gradient conditions optimized previously for modified nucleoside separation. A single hydrophobic compound was identified in the cytokinin region of the gradient, and limited quantities of the compound were prepared by HPLC fractionation of crude extracts. The compound demonstrated significant activity in a radioimmunoassay for cytokinins which detects N6-isopentenylated adenine derivatives. Boronate affinity chromatography indicated the compound is likely to be ribosylated and therefore a nucleoside. These and other tests indicate the compound has the most notable structural characteristics of a cytokinin. Spectral analysis and chromatographic comparison with cytokinin standards indicate the compound also has some unique structural features. Presence of the compound in extracts of an S. typhimurium mutant blocked for synthesis of tRNA-derived cytokinins excluded tRNA as a source for the compound and implicates existence of a tRNA-independent pathway for cytokinin biosynthesis in this bacterial species.

The control of bud dormancy in potato tubers. Measurement of the seasonal pattern of changing concentrations of zeatin-cytokinins

A radioimmunoassay, combined with high-performance liquid chromatography, has been used to analyse the zeatin-type cytokinins of potato (Solanum tuberosum L. cv. Majestic) tubers and tuber buds throughout growth and storage. During tuber growth, zeatin riboside was the predominant cytokinin detected in all tissues. Immediately after harvest, the total cytokinin concentration fell dramatically in the storage tissue, largely as a consequence of the disappearance of zeatin riboside. During storage, levels of cytokinins in the storage tissue remained relatively constant, but increased in the tuber buds. In the buds of tubers stored at 2°C there was a 20-to 50-fold increase in total cytokinin over six weeks, coinciding with the natural break of innate dormancy. At 10°C the rise in the level of bud cytokinins was slower, correlating with the longer duration of innate dormancy. Injecting unlabelled cytokinins into tubers in amounts known to induce sprouting gave rise to increases in cytokinin concentrations in the buds of the same order as the increase associated with the natural break of dormancy. Metabolism of injected cytokinins was greater in non-dormant than in dormant tubers. The roles of cytokinin concentration and the sensitivity of the buds to cytokinin in the control of dormancy are discussed.

T-DNA genes to study plant development: precocious tuberisation and enhanced cytokinins in A. tumefaciens transformed potato

Potato Line Mb1501B is a derivative of the cultivar Maris Bard (Solanum tuberosum), transformed with T-DNA from A. tumefaciens strain LBA1501. In culture it grew as frequently branching stunted shoots with a basal callus, lacking roots. These shoots did not form tubers. When grafted, Mb1501B shoots gradually became morphologically more normal and aerial tubers formed readily. Cultured Mb1501B shoots contained 100-200-fold higher concentrations of the biologically-active cytokinins zeatin, zeatin riboside and their corresponding side-chain o-glucosides than untransformed Maris Bard shoots. Cultured Mb1501B shoots contained approximately a 3-fold lower concentration of indole acetic acid (IAA). In grafted Mb1501B plants a 3-10-fold higher concentration of the active cytokinins was found compared with untransformed plants and no difference in IAA concentration.

Preparative and analytical high-performance liquid chromatographic methods in the synthesis and analysis of decomposition of nitrosourea nucleosides

Details are given for reversed-phase, adsorption, and aqueous ammonia-modified adsorption high-performance liquid chromatographic systems developed to separate 3'-chloroethylnitrosourea analogues of thymidine, 2'-deoxyuridine, and 5-fluoro-2'-deoxyuridine from their decomposition products and synthetic precursors. The effect of varying the substituent at the 3'- and 5-position on relative retention in each system is discussed. These systems are used to purify intermediates in the synthesis of these potent antineoplastic agents, and for the simultaneous analysis of the nitrosourea nucleosides and their breakdown products in kinetic studies of their decomposition. Application of these methods to the analysis of the kinetics of the breakdown of these compounds is demonstrated, with detection limits (signal-to-noise ratio = 2) in the 1-2 ng range.

Mass-spectrometric quantification of cytokinin nucleotides and glycosides in tobacco crown-gall tissue

the cytokinins of tobacco crown-gall tissue have been analysed by quantitative mass spectrometry using (2)H2-labelled cytokinin riboside 5'-monophosphates and (15)N4-labelled cytokinin glycosides as internal standards. The principal endogenous cytokinin of this tissue is zeatin riboside 5'-monophosphate. The biologically inactive 7-glucoside of zeatin is the most abundant basic cytokinin in the tissue. These findings expose the limitations of previously reported analyses of similar tissues, which were restricted to biologically active basic cytokinins. The present study demonstrates that the endogenous cytokinins of tobacco crowngall tissue show a clear correspondence to the range of metabolites formed when exogenous cytokinins are supplied to nontumorous tobacco cells.

Cytokinins in transfer RNA of normal and crown-gall tissue of Vinca rosea

cis-Zeatin riboside was identified in transfer-RNA hydrolysates from both normal and crown-gall tissue of Vinca rosea L. The trans-isomer was associated exclusively with the crowngall transfer-RNA. The importance of these observations is discussed in relation to biosynthesis of free cytokinins.

Cytokinin oxidase fromZea mays kernels andVinca rosea crown-gall tissue

Cytokinin oxidase has been partially purified from matureZea mays kernels and fromVinca rosea corwn-gall tissue. The molecular weights of the two enzymes, determined by gel filtration, are very different: 94,400 (±10%) forZ. mays and 25,100 (±10%) forV. rosea. Specificity studies have been performed using a large number of synthetic and naturally occurring cytokinins. Only a small number of these compounds serve as substrates and both enzymes exhibit similar substrate specificity. In agreement with other workers, a Δ(2) double bond in the N(6) side chain is essential for activity. The presence of glucosyl or ribosyl groups in the 7-or 9-position or an alanyl group in the 9-position of the purine moiety have little effect on their susceptibility to cytokinin oxidase, but O-glucosyl derivatives are resistant to oxidation. The relevance of these enzyme systems to studies on cytokinin metabolism and to the endogenous cytokinins is discussed.

Cytokinin biosynthesis in crown-gall tissue ofVinca rosea : The significance of nucleotides

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 [(14)C]adenine. The incorporation of radioactivity from [(14)C]adenosine into free cytokinins was also shown, but no incorporation of radioactivity was found when [(3)H]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 [(14)C]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.

Mass spectrometric measurement of zeatin glycoside levels in Vinca rosea L. crown gall tissue

The range of zeatin glycosides found in crown gall tissue of Vinca rosea L. has been quantified using a mass spectrometric isotope dilution procedure. Problems in the quantitative analysis of cytokinins in plant extracts are discussed.

Cytokinin metabolism in Phaseolus vulgaris L. : Identification of endogenous cytokinins and metabolism of [8-(14)C]dihydrozeatin in stems of decapitated plants

The major cytokinins in stems of decapitated, disbudded bean plants have been identified by enzymic degradation, Sephadex LH20 and reversed phase high performance liquid chromatography, and by combined gas chromatography-mass spectrometry as 6-(4-hydroxy-3-methylbut-trans-2-enylamino)-9-β-D-ribofuranosylpurine (zeatin riboside), 6-(4-hydroxy-3-methylbutylamino)-9-β-D-ribofuranosylpurine (dihydrozeatin riboside), and the 5'-phosphates of these compounds (zeatin ribotide and dihydrozeatin ribotide). Minor cytokinins in this tissue were tentatively identified as dihydrozeatin-O-β-D-glucoside and zeatin ribotide-O-β-D-glucoside. [8-(14)C-]Dihydrozeatin appeared to be rapidly metabolized to dihydrozeatin ribotide when supplied to segments of stems from decapitated plants. These results are discussed in relation to the metabolism and distribution of cytokinins in the whole plant.

Zeatin-9-glucoside, a major endogenous cytokinin of Vinca rosea L. crown gall tissue

Cultured crown gall tissue of Vinca rosea L. was found to contain, in addition to the previously reported cytokinins zeatin, zeatin riboside, and the 0-glucosides of these two compounds, relatively high levels of zeatin-9-D-glucopyranoside. This is the first conclusive identification of an endogenous cytokinin 9-glucoside.

Radioimmunoassays for trans-zeatin and related cytokinins

Radioimmunoassays for the quantitation of trans-zeatin and related cytokinins have been developed. Antisera produced against bovine serum albumin conjugates of trans-zeatinriboside have a high affinity (Ka=2.4.10(-11) M) for zeatinriboside and for zeatin, but show a negligible cross reaction to isopentenyladenosine (0.1%) and cis-zeatinriboside (0.4%), only a slight cross reaction to dihydrozeatin (1.7%), and no cross reaction at all to other purines, such as adenosine and related, compounds, was observed. The assays are sensitive and measuring ranges extend from 0.06-30 pmol (0.02-10 ng) of zeatinriboside. This has been achieved by employing as tracers immunoreactive zeatin derivatives with high-specific activity, (tritiated zeatinriboside-dialcohol: 8.37.10(11) Bq mmol(-1) and zeatinribosyl-[(125)I]tyramine: ca. 1.9.10(13) Bq mmol(-1). The detection limit is 40 fmol (15pg) for the assay employing the tritiated tracer, and assay reproducibility is high (variation coefficients of triplicates less than 5%). Several hundred assays can be completed in one day, and, due to the high specificity of this assay, crude extracts may be used for analysis. The course of zeatin levels in developing fruits of Lycopersicon esculentum cv. Moneymaker is given.