Thesis (Ph. D.)--Institute of Paper Chemistry, 1975. / Includes bibliographical references (p. 97-100).

Thesis (M. Phil.)--University of Hong Kong, 1981.

published_or_final_version / Botany / Master / Master of Philosophy

Abies concolor (white fir) is one of the many conifers often planted as an ornamental tree. Like so many other conifers, Abies is difficult to vegetatively propagate. Recent successes in using the techniques of tissue culture as a means of vegetatively propagating plants prompted the present study of applying these techniques to Abies.A review of the literature indicated that no conifer had ever been grown into plantlets by using the techniques of tissue culture. Only a very few reports exist for cellular differentiation although nearly thirty species of conifers have been grown in-vitro as callus.The review of literature also indicated that a variety of growth regulators, supplements and conditions of growth were utilized in promoting differentiation and the development of plants from callus. Since no consistent patterns emerge as guidelines for achieving differentiation, a proposal was made to test the effects of several growth regulators on callus tissue of Abies in hopes of causing differentiation and organogenesis.Terminal stem sections from the lower branches of a mature tree of Abies concolor were removed, sterilized and and placed on experimental solid media containing mineral salts, growth regulators and organic supplements. Growth of a callus occurred as a cream-colored friable mass on several of the media. When examined, however, the growth was found to consist of only parenchymatous cells. When transferred to a medium (G7) containing coconut milk, casein hydrolysate and 2 mg/l kinetin, compact, hemispherical nodules developed over a period of six weeks.A number of these nodules were fixed, embedded,'sectioned and stained with safranin and fast green. These were examined with a microscope and comparative photographs between this type of growth and the friable callus were made.Sections of the nodules showed a more compact arrangement of cells and an incomplete ring of growth consisting of cells arranged in radial files as if produced by a cambium. The center of the incomplete ring contained parenchymatous cells primarily, but scattered tracheid-like cells with bordered pits were also noted. Photographs of the well organized incomplete ring of growth and the tracheid-like cells were made.It can be concluded that differentiation of Abies concolor callus did occur on the G7 medium and that this represents a positive step toward organogenesis using the techniques of tissue culture.

Cowpea, Vigna unguiculata (L.) Walp is an excellent source of protein, vitamins and minerals and a major food crop many parts of Africa. Optimal production levels are hampered by insect pests and diseases. Biotechnological techniques such as tissue culture and genetic engineering can aid in the development of varieties with resistance to insect pests and diseases. The objective of this study was to investigate conditions necessary for the development of a reproducible tissue culture system that can be applied to regenerate transformed cells from culture. The in vitro manipulation of cowpea using Murashige and Skoog (MS) medium, auxins and cytokinins resulted in the formation of callus and rhizogenesis. Calli that were formed were separated into six classes based on color and texture. Yellowish friable callus, yellowish compact, soft yellowish callus and green and white were composed of largely vacuolated cells and were non-regenerative. Friable green callus was the most prevalent callus type and could form of roots in some hormone combinations. Green spots were formed on hard compact green callus. The green spots became nodular, forming root primordia and ultimately giving rise to roots. None of the six calli types gave rise to the formation of shoots. Embryogenic callus was induced from cowpea explants cultured on MS medium supplemented with dicamba and picloram. Embryogenic suspension cultures were initiated from callus induced on MS supplemented with 3.0 mg/L dicamba or picloram and conditions for maintenance of embryogenic suspension cultures were evaluated. Somatic embryos were formed in suspension cultures. Attempts to convert and germinate the somatic embryos resulted in the formation of callus or formation of appendages on the somatic embryos or in the death of the embryos. The appendages formed roots on prolonged culture. Further research is needed to determine appropriate optimal conditions for embryo conversion and germination and ultimately plant recovery from culture.

Call number: LD2668 .T4 1984 B46 / Master of Science

Thesis (MSc) -- Stellenbosch University, 1975. / No abstract available

Thesis (Ph. D.)--Institute of Paper Chemistry, 1975. / Bibliography: leaves 98-104.

In South Africa, there is a growing concern regarding the sustainability of bark harvesting due to the reduced availability of medicinal trees in natural areas and the slow growing and slow-reproducing nature of South Africa’s indigenous trees, of which some have specific habitat requirements and a limited distribution. With an estimated 80% of all Africans in South Africa still relying on plant material for their basic healthcare needs, approximately 200 000 traditional healers and an estimated 63 000 commercial harvesters, medicinal plants are being exploited to extinction. The aim of the study was to determine whether bridge-grafting could be used to restore growth in girdled Ocotea bullata and Curtisia dentata trees as these two medicinal tree species are listed on the South African Red List as ‘endangered’ and ‘near threatened’ due to overexploitation. These trees were also historically used in furniture production and general carpentry, which increased these trees’ vulnerability to extinction. Bridge-grafting is a technique widely described in horticultural literature but has not been used to restore growth in medicinal tree species with extensive harvesting damage. Metabolomics as analytical method is a relatively new science, but it is very useful, accurate and repeatable in obtaining knowledge on the metabolites present in a plant, and for determining the concentrations of metabolites. NMR metabolomics is, however, not sensitive enough to quantify metabolites with very low concentrations such as plant hormones. The results achieved showed that O. bullata and C. dentata responded differently to girdling and bridge-grafting regarding location of callus initiation, callus development, rate of callus development, basal shoot initiation and development and their sucrose source-sink relationships. NMR metabolomics showed that seasonality was an important factor affecting metabolite responses in both species. NMR metabolomics also showed that after one year, there were no differences in responses above and below the girdle wounds, nor were there differences between the grafted trees and the normal control trees. iv Although the method of bridge-grafting was successful in restoring the growth of O. bullata and C. dentata with this study, much more research needs to be conducted to prevent endangered girdled medicinal trees from becoming extinct, to maintain tree species diversity, genetic diversity and biodiversity. / School of Environmental Sciences / M. Sc. (Nature Conservation)