A review of the literature indicated that the purine cytokinin 6-(benzylamino)purine (SA) may be converted to a wide range of metabolites. Although the functional significance of these metabolites remains obscure, cytokinin physiologists have essentially classed them as either active or inactive. Inactivation of cytokinins is considered to proceed via catabolic oxidation (side-chain cleavage), or N-conjugation with glucose or alanine moieties. The literature survey was hampered by the confusing array of synonyms which have been coined for cytokinin metabolites. Accordingly, a working system of (semi-systematic) abbreviations was devised which accommodated all groups and classes of purine cytokinins. Prior to commencing metabolic interactive studies, it was necessary to resolve the contentious issue associated with the successful extraction of cytokinin nucleotides. Five-week-old soybean callus was fed [8[-14]C]BA and subsequently extracted using four widely used cytokin in extraction techniques. Techniques compared were a modified Bieleski method, 80% ethanol with tissue homogenisation, 80% ethanol without homogenisation, and boiling ethanol. All four procedures produced similar results, showing that all metabolites of SA, including the nucleotide, were adequately extracted. It was concluded that the extraction of nucleotides with Bieleski solvents did not warrant the inconvenience. Auxins have been shown to interact with cytokinins in the regulation of many physiological processes, although little is known of the mechanisms of interaction which proceed at the metabolic level. Previous investigators have shown that auxin promoted cytokinin degradation through catabolic oxidation, Shoot-apex and seed derived cell suspensions of Dianthus zevheri subsp. natalensis were incubated with [8[-14] C]BA for between 30 minutes and 48 hours in the presence of both low (2 mg l-1) and high (4 mg 1¯¹) levels of exogenously supplied 2,4-dichlorophenoxyacetic acid (2,4-D), In both systems, the auxin 2,4-D was shown to promote SA inactivation through 7-glucosylation (N-conjugation). This observation represents the first report of auxin-promoted cytokinin N-conjugate formation. The auxin effect on metabolism was transient in the case of shoot-apex, but not in seed-derived systems over a 48 hour period. Formation of the 7-glucoside of SA was dose-dependent in apex-derived cultures. Further studies were undertaken with indole-3-acetic acid (lAA) and α-naphthaleneacetic acid (NAA). It was found that auxin-promoted 7-glucosylation of SA was only minimally effected by these two auxins. In comparable studies with soybean suspension cultures (Glycine max cv. Acme), 2,4-D-promoted catabolic oxidation was observed between 18 and 48 hours, following application of phytohormones. The main catabolite was tentatively identified as adenosine-5'-monophosphate (AMP), based on chromatographic characteristics. Carrot (Daucus carota) cell suspensions similarly supplied with 2,4-D and SA maintained a large active cytokinin pool. Neither substantial oxidative nor Nconjugative processes were observed. Instead, there was a transient effect by 2,4- D on the relative formation of the riboside and the 7- and 9-glucosides of SA. The effect of auxin on the metabolism of SA thus varied with the species and system investigated. Generally, auxin promoted (rather than inhibited), the formation of inactivated metabolites and catabolites of SA, possibly by the induction of relevant enzyme systems. Transient auxin effects on the metabolism of SA are discussed in relation to the role of the auxin/cytokinin balance in the induction of developmental processes. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1993.

The initiation and development of adventitious roots in cuttings are highly complex processes, influenced by both endogenous and exogenous factors. These vary from the environmental factors prior to the striking of the cutting, to the anatomical and physiological factors, within the stem. Encompassed are the nutrient status, physiological age and degree of differentiation of the tissues, and the balance of endogenous rooting inhibitors and/or promoters (including hormones). The role of cytokinins in root initiation and development has been perceived as that of an inhibitor. This investigation considered several aspects of the role played by cytokinins in the process of root development. A qualitative/quantitative analysis of the cytokinin-like activity in stem cuttings of several plants, including both easy- and difficult-to-root species was conducted on a comparative basis. There was no clear correlation between the type / level of cytokinins detected in the cuttings and the relative ease of root formation. Both qualitative and quantitative changes in the compounds exhibiting activity in the soybean callus bioassay were observed over the period of root formation in Impatiens stem cuttings. The effects on root formation in cuttings of exogenously applied auxins and cytokinins were investigated. Auxins generally promoted root number and elongation at relatively high concentrations (10[-4] M), but showed less effect on lateral root initiation and development. At high concentrations, cytokinins strongly inhibited root development, but did promote lateral root growth. In suspension culture, the effect of these hormones differed slightly, with IAA and IBA having no significant effect on root development, but NAA strongly stimulating lateral root initiation. Zeatin (10¯¹¹ M) significantly increased root length and the number of lateral roots produced. The effect of treatment of the stem cuttings with potassium permanganate and centrifugation was examined. While both these treatments have been perceived to increase root production in cuttings, no significant improvement in rooting ability following centrifugation (relative to the control) was observed. Impatiens cuttings centrifuged in the presence of distilled water showed a significantly reduced rooting ability relative to those centrifuged in the dry state. Treatment with an 8-hour pulse in 0.05 % potassium permanganate significantly increased the average root length. These treatments had an effect on the cytokinin levels and distribution in the stem cuttings. Slightly higher levels of cytokinins were associated with the increase in root number and length in both experiments. / Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 1996.

Intact or decapitated Pisum sativum seedlings were used to investigate the correlative inhibition of lateral buds by the shoot apex - a developmental process known as apical dominance. Apical dominance is considered to be regulated by the relative ratios of growth regulators, especially auxin and cytokinin, and resource availability in the plant. This study considered the role of cytokinins in the regulation of correlative inhibition, and was closely linked to theoretical models of auxin and nutrient gradients in the whole plant. Firstly, the response of all lateral buds on the plant to decapitation of the shoot apex, and the subsequent growth of these buds, was documented. The pattern of lateral bud branching following decapitation, noted to change with increasing age of the plant, was found to be consistent with the view that apically synthesized auxin, moving basipetally, exerts an inhibitory influence on lateral bud growth. Removal of selected lateral buds on decapitated plants which left various combinations of buds to compete indicated that correlation between lateral buds on the same plant was likely an important factor controlling the patterns of lateral bud branching. Secondly, a quantitative study of the biological responses which result from the application of a cytokinin to a lateral bud were performed. The different abilities of ten cytokinins tested to release lateral buds from dominance paralleled their activity in a soybean callus bioassay, and were likely a result of the intrinsic activities of the cytokinins due to their structure and their subsequent rr.etabolism in the plant following application. A consistent feature of these experiments was the low biological activity of isopentenyladenine in relation to the high activity of zeatin. Further investigation of the role of isopentenyladenine and zeatin in apical dominance control indicated that lateral buds differed in their sensitivity to these two cytokinins. On decapitated plants, lateral buds were more able to utilize applied isopentenyladenine, and high zeatin concentrations were no longer supraoptimal for growth. Finally, the metabolism of [³H] isopentenyladenine in the intact plant or in isolated explants was investigated in an attempt to relate the biosynthesis, transport, interconversion and degradation of cytokinins to the developmental process of apical dominance. Comparison of the uptake and metabolism of [³H] isopentenyladenine by isolated organs of Pisum sativum indicated that the roots, leaves and stems, but not isolated lateral buds had the capacity to metabolise [³H] isopentenyladenine to zeatin metabolites. This metabolite activity was very notable in the stem, where it occurred as a gradient and was related to the age of the plant. Auxin was considered to be the factor controlling this distribution of cytokinin metabolic activity in the stem since parallel gradients had been noted in the patterns of lateral bud branching and the response of buds to cytokinin application. Indeed, it was shown that indole-3-acetic acid affected the metabolism of [³H] isopentenyladenine in isolated stem sections. These results are discussed in relation to the control of lateral bud growth via the auxin mediated distribution and metabolism of root produced cytokinins in the shoot system, necessary for the release of apical dominance. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1988.

Thesis (M.S.)--Oregon State University, 1989. / Typescript (photocopy). Mounted photographs. Includes bibliographical references. Also available on the World Wide Web.

Thesis (Ph. D.)--Oregon State University, 2008. / Printout. Includes bibliographical references (leaves 80-103). Also available on the World Wide Web.

Magister Scientiae (Biodiversity and Conservation Biology) - MSc (Biodiv and Cons Biol) / Randomized block experiments were conducted to examine the putative amelioratory effects of kinetin or gibberellic acid at concentrations (0, 4, 12.5, 40, and 125 μM) in Erucastrum strigosum plants subjected to a salinity series (0, 100, 200, 300, and 400 mM NaCl) in the greenhouse. When the highest salinity concentration (increased stepwise) was reached, growth effects in relation to water and cation content of the plants were evaluated. Growth and water content were reduced progressively with salinity treatments. Na+ concentration accumulated with salinity treatments to levels that were much higher than that of other cations (K+, Ca2+ and Mg2+) in both organs. However, it is noteworthy that Na+ distribution was more in shoots than in roots. In kinetin treated plants, shoot growth decreased whilst root growth increased with moderate hormonal treatments.

No description available.

Soybean, Glycine max (L.) Merr., fruits 10-25 mm long contained nine fractions having cytokinin-like activity detectable by the Amaranthus bioassay. These fractions were derived from purification of extracts from 15 g of immature fruits. The fractions were purified by polyvinylpyrrolidone (PVP), paper, Sephadex LH-20 and high performance liquid chromatography. The fractions separated on the basis of polarity into polar, moderately polar and relatively non-polar groups, compared to zeatin. The polar fraction was the single most bioactive fraction and the active substance was tentatively identified as a zeatin glucoside or zeatin riboside glucoside. The moderately polar fraction contained bioactive substances that co-eluted with zeatin and zeatin riboside in four chromatographic procedures. The relatively non-polar fraction contained two bioactive components, one chromatographically resembling 2iPA, and the second less polar. A conjugated cytokinin was released from the original aqueous phase by alkaline phosphatase hydrolysis. This substance co-eluted with zeatin riboside on Sephadex LH-20. Further purification and analysis by multiple ion monitoring GC-MS did not yield conclusive identification of the cytokinins. Based on bioassay, the biological estimates of cytokinin-like substances present in the extracts were below the detection limit of the GC-MS. Obtaining sufficiently large samples of soybean fruits at the proper stage of physiological interest complicated definitive structural identification based on the purification and identification techniques used. / Ph. D.

Exogenous application of BA (0, 50, 100 mg ul--1) had no significant effects on tolerance of chili peppers to salt (--0.75 MPa NaCl:CaCl₂, 3:1, w/w) as measured by vegetative and reproductive weights, numbers of reproductive structures, transpiration and total chlorophyll. When peppers were applied with microliter amounts of ¹⁴C labelled benzyladenine (BA; 44,400 dpm 1⁻¹), BA was translocated primarily acropetally from the site of application. Regardless of application site, translocated BA was ported primarily to expanding leaves, and BA was more readily absorbed by leaf as opposed to stem surfaces. Exogenous application of BA (0, 50, 100 mg ul⁻¹) had no significant effects on tolerance of chili peppers to salt (-0.75 MPa NaCl:CaCl₂, 3:1, w/w) as measured by vegetative and reproductive weights, numbers of reproductive structures, transpiration and total chlorophyll.

The endogenous cytokinin levels in the brown alga Ecklonia maxima (OSBECK) PAPENF., and the effect of applications of the seaweed concentrate (Kelpak 66) prepared from this alga, on the growth and yield of various plants was investigated. Tentative identification of the cytokinins present in Ecklonia maxima using High Performance Liquid Chromatography revealed the presence of cis and trans-ribosylzeatin, trans-zeatin, dihydrozeatin and isopentenyladenosine. Seasonal and lunar variations in the endogenous cytokinin levels in fresh and processed Ecklonia maxima material were investigated. Lamina, stipe and holdfast regions of one, two and three metre plants harvested from February 1981 until January 1982 together with samples of processed material from the normal production run, collected over the same period were used in this investigation. Analysis revealed both qualitative and quantitative changes in the cytokinin levels which were closely correlated to the seasonal patterns of growth of Ecklonia maxima. During summer zeatin, ribosylzeatin and their dihydroderivatives were responsible for most of the detected activity. The cytokinin glucosides increased above the levels of free cytokinins during winter. The lunar cycle study of material harvested on a daily basis during April - May 1983 revealed marked fluctuations in the cytokinin levels in the various tissues of two metre plants which were closely correlated with the phases of the moon. Greenhouse trials were conducted to determine the effects of the commercially available seaweed concentrate (Kelpak 66) on the growth of Lycopersicon esculentum MILL. plants in nematode infested soil. Kelpak 66 at a dilution of 1 : 500 improved the growth of treated plants significantly, irrespective of whether it was applied as a foliar spray at regular intervals, or whether the soil in which the plants were grown was flushed once with the diluted seaweed concentrate. Root growth was significantly improved whenever the seaweed concentrate was applied. Associated with this improved root growth was a reduction in the infestation of Meloidogyne incognita (KOIFORD and WHITE) CHITWOOD. Finally, the effect of seaweed concentrate and fertilizer applications on the growth and endogenous cytokinin content of Beta vulgaris L. and Phaseolus vulgaris L. plants was investigated. Seaweed concentrate at a dilution of 1 : 500 applied as a foliar spray improved the growth of treated plants significantly, irrespective of whether it was applied on its own or together with a chemical fertilizer. Root growth and the endogenous cytokinin content of these roots increased with seaweed concentrate application. Increases were also detected in the cytokinin content of fruits of Phaseolus vulgaris plants treated with seaweed concentrate. Associated with this increase in the cytokinin content was an increase in the dry mass of the fruit from treated plants. The significance of these findings and the possible relationship between the endogenous cytokinins present in Ecklonia maxima and the effect of the seaweed concentrate on plant growth is discussed. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1984.