by Wing-kin Yip. / Bibliography: leaves 79-83 / Thesis (M.Phil.) -- Chinese University of Hong Kong, 1983

"The in vitro addition of plant growth regulators (i.e. phytohormones) to Agrobacterium transformed hairy root cultures affects morphological and biochemical changes, resulting in altered growth and secondary metabolite accumulation rates in root tissues. Significant increases in both growth and secondary product accumulation have been observed, upon incubation with phytohormones, in some species. Consequently, the use of phytohormones in vitro has received increasing attention as a potential means for increasing those plant secondary products notoriously produced in small quantities. However, currently little is known about the specific effects of phytohormones on growth and secondary metabolism. The Chinese herb Artemisia annua L. produces artemisinin, an effective antimalarial therapeutic. Efforts to increase the amount of artemisinin via chemical synthesis or field-grown crops have met with huge costs and disappointingly low yields, respectively. Agrobacterium transformed hairy root cultures of A. annua (Clone YUT16) produce artemisinin and undergo rapid growth compared to non-transformed, making them a good model system to study secondary metabolite production. Demonstrated herein is the first definitive evidence, by any hairy root species, of a favorable response to exogenous combinatorial hormone application as well as the development of a two-stage culture system alluding to optimal growth and artemisinin production conditions in A. annua hairy roots. Furthermore, analysis of artemisinin and biomass accumulation in A. annua hairy roots in the presence of phytohormones has revealed effective individual as well as combinatorial phytohormone concentrations suitable for increasing single and bulk root growth, and artemisinin production. The effectiveness of an optimal phytohormone combination, with respect to time of addition, its relationship to inoculum size, and its combination with the provision of fresh nutrients and or mechanical stress to the roots is also described resulting in artemisinin yields of up to 0.8 ìg/g F.W. Although the findings contained herein are not yet optimized they do, however, argue for the potential usefulness of a two-stage production scheme using phytohormones to increase plant secondary metabolite production in vitro."

Photocopy of typescript. / Digitized by Kansas Correctional Industries

Many mycorrhizosphere microorganisms can produce plant growth regulating compounds in vitro. Plant growth regulating compounds are known to mediate root growth and development. In reforestation practices, conifer tree seedling growth and survival are linked to rapid root growth and development after outplanting. Multifactorial experiments were conducted to document variations in conifer seedling growth, survival and endogenous root indole acetic acid (IAA) content as influenced by exogenously applied plant growth regulators and inoculation with ectomycorrhizal fungi capable of differential in vitro IAA and ethylene production. Capacity for in vitro IAA and ethylene production by mycorrhizal fungal isolates was partially correlated to levels of endogenous root IAA and root growth in inoculated seedlings as well as field transplanted nursery-grown seedlings. Although degree of correlation usually varied with fungal isolate as well as conifer species, IAA-mediated changes in root growth and seedling survival could indirectly be attributed to in vitro fungal plant growth regulator production capability. Exogenous application of plant growth regulating substances at different times during seedling growth and development resulted in significant changes in growth, survival and endogenous root IAA content of both experimental seedlings and field transplanted nursery-grown seedlings. Although effects varied with conifer species and stock types, IAA mediated increases in root growth and survival are projected to be cost beneficial. These results are not only indicative of the complexity of interactions which can occur between symbionts in the mycorrhizosphere but also suggest potential methods for manipulating plant growth regulator mediation of conifer root growth for practical purposes in reforestation. / Graduation date: 1994

Thesis (Ph.D.)--University of Nebraska-Lincoln, 2009. / Title from title screen (site viewed October 13, 2009). PDF text: xiii, 173 p. : col. ill. ; 6 Mb. UMI publication number: AAT 3355630. Includes bibliographical references. Also available in microfilm and microfiche formats.

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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.

Thesis (Ph. D.)--Oregon State University, 1990. / Typescript (photocopy). Includes bibliographical references. Also available on the World Wide Web.