Ceratotheca triloba (Bernh.) E. Mey. ex Hook. f., commonly known as the wild foxglove, is a fast growing annual that is indigenous to southern Africa. The surface of the plant is covered with fine, hair-like trichomes, which exude sticky, aromatic substances. The plant is traditionally used to treat various abdominal ailments, insect infestation of the skin and leaf extracts are administered to induce abortion. In order to provide a scientific basis for the medicinal properties of C. triloba, this study was initiated to characterise the morphology and ultrastructure of the foliar trichomes and to determine the chemical composition of the secretion. Phytochemical tests and a range of microscopic techniques including stereo microscopy, scanning electron microscopy, transmission electron microscopy, histochemistry and fluorescence microscopy were used. Leaf surface imaging with stereo microscopy and SEM indicated the presence of two morphologically distinct glandular trichomes, capitate and peltate. The capitate trichomes are tall, consisting of a single basal cell, 2-4 stalk cells, a neck cell and a head that is made up of four secretory cells. Capitate trichomes of up to 14 stalk cells were observed on the abaxial side of flower petals. The peltate trichomes consisted of a basal cell, a single stalk cell and a multicellular head. The peltate trichome head generally consisted of four cells, but occasionally were seven or eight-celled. Fully developed trichomes were found to be concentrated on emergent leaves and probably serve protective function. The density of trichomes decreased as the leaf expanded. TEM showed that the secretory cells of peltate trichomes contained centralised nuclei and numerous peripheral vacuoles. Numerous mitochondria and ER cisternea were found throughout the cytoplasm. Osmiophilic plastids which were found near nuclei and golgi apparatus were in close proximity to the peripheral vacuoles. Similar observations were made for the stalk cells of both trichomes. The head cell of capitate trichomes however, contained large amounts of osmiophilic substances, ER cisternae and mitochondria. The head cells of peltate trichomes store the secretory product in vacuoles and secrete them upon cell rupture or cell dissolution. The secretory product of capitate trichomes is secreted through the cell membrane via an eccrine mode of secretion. Peltate and capitate trichomes appear to be secreting similar compounds, but the composition of each compound in the secretory material may vary between the trichomes. Histochemical and phytochemical tests reveal that the secretions are comprised of mucilage, phenolic compounds, lipids, flavonoids, tannins, saponins and fixed oils which may contribute to the medicinal properties of C. triloba. The observations made in this study provide useful information for additional research in the Pedaliaceae, and specifically in C. triloba. Future studies should isolate the active compounds for antimicrobial and antioxidant testing. Cytotoxicity testing should also be undertaken to test safety and efficacy of the active compounds. / Thesis (M.Sc.)-University of KwaZulu-Natal, Westville, 2012.

Nitrogen fixation of blue-green algae associated with Avicennia marina (Forssk.) Vierh. pneumatophores and wet and dry surface sediments were investigated in the Mgeni Estuary mangrove swamp by means of the acetylene reduction technique. Optimum partial pressures of acetylene ranged from 0,15 to 0,2 atm. for the different habitats. A lag phase of 3 h was observed in all habitats, followed by a period of linear ethylene production of 42 h for the pneumatophores and 72 h for the wet and dry mat areas. An assay period of 24 h was employed in all habitats. Laboratory studies revealed percentage moisture and temperature to be the prime factors influencing ARA (acetylene reduction activity) in all habitats and rates were highest under submerged conditions and at 22˚C. Short-term variations in ARA and salinity in the wet and dry mat areas, measured at 6 day intervals, were also related to percentage moisture. High concentrations of inorganic nitrogen (between 1 and 5 mg 1-1) significantly depressed ARA in all habitats. Increases in ARA occurred with increase in light intensity up to 40 μE m -2 s-1, with negligible dark rates being recorded in the wet and dry mat areas. Significant dark rates of ARA and stimulation of ARA by sucrose in association with the pneumatophores indicated that bacteria may also be contributing to ARA in this habitat. No organic carbon stimulation was noted in the other sites. Salinity had little effect on ARA over the range generally experienced in each habitat. Field studies revealed a marked seasonal variation in ARA, with summer maxima of 78, 678 and 341 nmol C2H4 cm-2 24 h-1 associated with the pneumatophore, wet and dry mat areas respectively. This coincided with maximum nitrogen-fixing blue-green algal numbers, temperature, light intensity and day length. No seasonal variations in organic carbon, inorganic nitrogen, salinity, percentage moisture or bacterial numbers were apparent. Rates of bacterial ARA associated with decomposing litter of A. marina were highest under exposed conditions and reached a maximum of 25 935 nmol C2H4 g dry wt -1 24 h -1 after 3 weeks. Maximum rates of ARA under submerged conditions of 5394 nmol C2H4 g dry wt -1 24 h -1were reached after 4 weeks of decomposition. An increase in percentage nitrogen occurred during decomposition and was greatest under submerged conditions. Rates of decomposition were highest under exposed conditions. It was estimated that nitrogen fixation by blue-green algal communities supplies 23,8% of the annual nitrogen requirements of the mangrove swamp. / Thesis (M.Sc.)-University of Durban-Westville, 1987.

The tribe Desmodieae has a pantropical distribution and is one of the most advanced tribes in the subfamily Papilionoideae. Despite this fact, the tribe was already present in the fossil record of the early Tertiary and so the Papilionoideae appear to be much older than is currently accepted. With its greatest centres of development in tropical Asia and America, Africa is relatively poorly endowed and only four genera comprising sixteen species occur in the Flora of southern Africa. Many of these species are widespread in the old World tropics and the few African endemics appear to be closely related to them. Desmodium is the largest genus with the bulk of species belonging to the Asian subgenus Sagotia. Of the two sections of Sagotia represented in Africa, section Nicolsonia is clearly more derived than section Heteroloma, showing many characters intermediate between Heteroloma and the considerably more derived genera Alysicarpus and Lespedeza. Other Desmodium species either of the Old or New World have often become naturalised as weeds in Africa. Pseudarthria is a genus derived by an aneuploid increase of the basic x = 11 for the tribe rather than an aneuploid decrease as in the case of Alysicarpus and Lespedeza. A re-count of the chromosome number of P. hookeri (2n = 26) matches the count obtained in another species of Pseudarthria for the first time. Flowering strategy and flower structure in the tribe are the result of intense coevolution with the ecological requirements of skilled bee pollinators and although many bees can trip Desmodieae flowers, only a relatively few high energy demanding, traplining bees are able to bring about effective pollination. The overall breeding system represents a fine balance between the need for selfing and the need for outcrossing in order to produce enough seed of sufficient quality to survive in unstable environments. / Thesis (M.Sc.)-University of Durban-Westville, 1984.

A cladistic analysis of 51 generic and infrageneric taxa in the tribe Indiqofereae (Papilionoideae) is presented, comprising q 570 species in Africa and Madagascar. Traditionally, 4 genera have been recognized: Phylloxylon (q 5 species), Rhynchotropis (2 species), Cyamopsis (q 4 species) and Indigofera (510-520 species in Africa). 3 genera have been reinstated, i.e. Vaughania (11 species), Indigastrum (11 species) and Microcharis (q 26 species). Vaughania was previously considered to be a monotypic genus (later placed in synonomy under Indigofera); the others have recently been treated as subgenera of Indigofera. A new subgenus is described in Indigostrum. (subgenus Argyraeae Schrire) as well as 17 new sections and one subsection in Indigofera. 18 infrageneric taxa in Indigofera are specified at a new rank. Taxonomic affinities with neighbouring tribes are discussed. A historical review is given of infrageneric subdivision. in Indigofera along with a newly proposed classification of infrageneric taxa in Africa. The cladogram is used to study character evolution in the tribe; from a) an ecological perspective (by identifying aptations) and b) a phylogenetic perspective (by identifying constraining interactions between morphologies). Aptations and critical morphologies are mapped on the cladogram to interpret developmental constraints, and the order and direction of character transformations. Key morphologies are a class of developmental constraints defined here for the first time. The cladogram and character analyses are used to interpret a phylogenetic tree of the tribe in Africa. Major phase. in the evolution of Indigofereae are hypothesized on the basis of developmental constraints, phytogeography and ecology. A taxonomic revision above the species level in Africa is presented, including keys and descriptions of genera and infrageneric taxa in Indigofera. Species of Indigofereae occurring in tropical Africa are listed, while a synopsis is given of southern African species with literature citations, synonymy and typification. 29 new combinations are made in Microcharis and Indigastrum. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1991.

The southern African species of Leonotis (Pers.) R. Br. are revised. Nine taxa are recognised including a new species and two new subspecies. A multidisciplinary approach was adopted involving: floral, vegetative, seedling and fruit morphology, karyology, palynology, pollination biology, phytogeography, phytochemistry and cladistics. Of these characters the most important in delimiting species is leaf morphology. Phytochemistry revealed qualitative and quantitative differences in essential oils between taxa. Germacrene is the dominant essential oil in seven species, particularly in L. dubia E. Mey. and L. nepetifolia (L.) R. Br. Caryophyllene dominates in L. randii S. Moore. Although certain species have characteristic aromas, no inter-specific differences are apparent in the levels of α-copaene, the dominant volatile essential oil extracted with Tenax. Essential oil data is in partial agreement with the phylogeny and species concepts presented in this document. Omithophily accounts for most fruit set in perennial species but in the annual species (L. nepetifolia) autogamy prevails. Neither omithophily nor entomophily improved nutlet vigour which was gauged from nutlet germination. Leonotis species are predominantly pollinated by a variety of sunbirds, although bees are also involved. Nectar is sucrose-dominant in perennial species but hexose-dominant in the annual. The majority of species are concentrated along the eastern seaboard with the eastern Cape forming the centre of diversity. The widespread distribution and tropical affinities of L. leonurus (L.) R. Br., suggest an origin for the genus in tropical Africa. Migration to southern Africa and subsequent speciation are suggested. Habitat diversity and edaphic conditions probably played an important role in the evolution of narrowly distributed xerophytic species. A cladistic analysis re-emphasised that Leonotis is a monophyletic group of closely related species. The lack of floral divergence in perennial species indicates the constraints imposed by ornithophily. The annual, L. nepetifolia, is highly derived and displays numerous autapomorphies. The morphology, distribution and tropical affinities of L. leonurus are interpreted as pleisiomorphic. The proposed phylogeny is reasonably compatible with phytogeographic data. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1995.

Sugarcane has become an increasingly important crop in recent years, with South Africa featuring as one of the prominent producers. This has led to a significant growth in the South African sugarcane industry, translating into an increased demand for planting material. Although this demand is now satisfied by recent biotechnological advancements such as protocols for somatic embryogenesis to increase the production of planting material, such techniques are limited as a result of the progressive loss of the embryogenic potential of calli over time. In order to facilitate management of this material, it is desirable to develop a protocol for the long-term storage of the germplasm. This study reports on investigations of the different parameters that influenced the cryoprocess in attempts to develop a protocol for the successful cryopreservation of sugarcane somatic embryos of the 88H0019 variety. Experiments were carried out to determine in vitro culture conditions for successful induction of somatic embryos via both the direct and indirect routes of micropropagation. A suitable regeneration medium for plantlet establishment pre- and post-cooling was established (Chapter 2). Investigations were also carried out to ascertain the responses of somatic embryos to both rapid and slow dehydration techniques (Chapter 3). Finally, several cooling techniques (both slow and rapid), were applied, on partially dehydrated somatic embryos, either without, or after cryoprotection, in an attempt to achieve survival after cryopreservation of the somatic embryos (Chapter 4). Both directly- and indirectly-derived somatic embryos were converted, most successfully, on full strength Murashige and Skoog medium without addition of plant growth regulators. The initial mean water contents of directly- and indirectly-derived somatic embryos were not significantly different from each other (8.38±0.19 g g-1 and 8.45±0.33 g g-1 [dry mass basis], respectively). The percentage conversion at these water contents was also not significantly different; 97% for directly- and 98% for indirectlyinduced embryos. Slow dehydration by culture on a series of media with increasing concentrations of sucrose (from 0.2 M to 1.2 M) for a period of 48 h each was the most effective technique, with water content being reduced to 0.94±0.03 g g-1 and 0.95±0.02 g g-1 after dehydration on media containing 1.0 M sucrose, while maintaining between 98% and 100% conversion, respectively. Of the various cryoprotectants tested, proline and casamino acid had the least adverse effects on the somatic embryos. The encapsulation-vitrification cooling technique was the most efficient of all techniques employed. The best conditions involved encapsulation of embryo clumps in a solution of MS medium with 3% (w/v) Na-alginate and loading solution containing 2 M glycerol plus 0.4 M sucrose, followed by infiltration and dehydration at 0°C for various time intervals (0, 5, 10, 15, 20, 25, 30 min) with 1 ml PVS2 solution and thereafter, rapid immersion in liquid nitrogen. Under such conditions, 30% of the cryopreserved somatic embryos retained viability, going on to form callus from which shoots and roots were produced. Although somatic embryos of sugarcane of the local variety 88H0019 have proved to be recalcitrant to cryopreservation, the results obtained with explants that had been processed by encapsulation-vitrification suggest that this approach may be worth pursuing and refining. / Thesis (M.Sc.)-University of KwaZulu-Natal, Westville, 2009.

Taxonomic confusion associated with Combretum Loefling, subgenus Combretum (Combretaceae) resulted in this investigation into the validity of sectional limits within the subgenus in southern Africa. Eight sections, together with their species and infraspecific taxa, totalling 29, are currently recognised in this region. Light and scanning electron microscopy on herbarium samples representing the taxa concerned were used to observe a final total of 171 selected characters. Data from individual specimens were collected numerically and processed to produce phenograms using Rohlf's NTSYS-pc program; also to produce descriptions in natural language format. A data processing program, TAXON, was specially designed and implemented to facilitate the desired processing and output. With the possible exceptions of Macrostigmatea and Ciliatipetala which require further investigation before certainty is reached, currently recognised sections were found to be valid and the limits between them acceptable. The main sources of confusion in this subgenus were found to lie in certain currently recognised species and their infraspecific taxa. These taxa were observed not to be distinct. The status of non-distinct species has been changed whenever clear evidence exists in favour of these changes. Other changes to species and infraspecific taxa have been recommended, but only to be implemented if supportive evidence is found after further investigations. Changes of status have been made in section Angustimarginata Engl. & Diels, where C. caffrum (Eckl. & Zeyh.) Kuntze and C. woodii Dummer have become synonyms of C. erythrophyllum (Burch.) Sond., and C. vendae Van Wyk has become a subspecies of C. erythrophyllum (Burch.) Sond., i.e. ssp. vendae (Van Wyk) Rodman comb. & stat. nov. (ined.); and in section Spathulipetala Engl. & Diels, where C. mkuzense Carr & Retief ,(section Macrostigmatea Engl. & Diels) has become a synonym of C. zeyheri Sond. C. collinum ssp. gazense (Swynn. & Bak.F.) Okafor, section Metallicum Fresen., has been changed to C. collinum ssp. coriaceum (Schinz) Rodman (ined.) in accordance with international botanical nomenclature. / Thesis (M.Sc.)-University of Durban-Westville, 1990.

To study the short-term effect of hydrogen peroxide on plant metabolism aminotriazole (2 mM), a catalase inhibitor was applied through the transpiration stream of pea seedlings and the gas exchange characteristics, ascorbate peroxidase, glutathione reductase and catalase activities, and the levels of hydrogen peroxide, glutathione and formate were determined. CO2 assimilation rates were inhibited after the addition of aminotriazole: photorespiratory conditions (high 02 and low CO2 concentrations, high light intensities) exascerbated the inhibition. CO2 response curves showed that aminotriazole reduced both the RuBP regeneration rate and the efficiency of the carboxylation reaction of Rubisco. The inhibition of the CO2 assimilation rate during the first 100 minutes after the addition of aminotriazole was alleviated by feeding PGA through the transpiration stream. Catalase activity was completely inhibited within 200 minutes of aminotriazole application, but there was no concomitant increase in the hydrogen peroxide concentration, suggesting that hydrogen peroxide is metabolised by an alternative mechanism. The treatment had no effect on ascorbate peroxidase and glutathione reductase activities or total glutathione pool size, but greatly increased formate levels. These results suggest that hydrogen peroxide is metabolised by reacting with glyoxylate to form formate and CO2, The increased production of formate may reduce the flow of carbon through the normal photorespiratory pathway and may be used anapleurotically as a precursor of products of l-C metabolism other than serine. This would prevent the return of photorespiratory carbon to the BensonCalvin cycle in the form of 3-PGA. It is proposed that when RuBP regeneration levels are low high formate levels may be an effector of Rubisco, and competitively inhibit the binding of CO2 and 02. These results suggest that under photorespiratory conditions the uninterrupted flow of carbon through the photorespiratory pathway is fundamental to the functioning of photosynthetic metabolism. / Thesis (M.Sc.)-University of Natal, Durban, 1990.

The genus Scleria Bergius (Cyperaceae) in Southern Africa is critically examined, and the generic limits reviewed The taxonomic position of the genus in the family is examined. Diagnosis of the tribe Sclerieae is altered to circumscribe Scleria as the only genus, and diagnoses of the tribes Bisboeckelereae and Sclerieae are made. Infrageneric limits are re-assessed and two subgenera, Scleria and Hypoporum recognised, the relationship of which is postulated as co-lateral, not filial. Evidence is presented that ecological specialisation in subgenus Hypoporum has resulted in taxa which are adapted to open, seasonally dry, temperate habitats, whereas ecological specialisation in subgenus Scleria has given rise to taxa which are adapted to shady, wet, tropical and subtropical habitats. Taxa in subgenus Hypoporum are slender, usually narrow-leaved annuals, or perennials with annual aerial parts, that is, they have evolved drought/cold escape mechanisms, the annuals by completion of the life cycle in a season, the perennials by withdrawal of food reserves into a protected, subterranean perennating organ and sometimes also into enlarged culm-bases. Taxa in subgenus Scleria are more-or-less robust, usually broad-leaved perennials, or, less often, annuals. With few exceptions the plants are evergreen and do not manifest drought/cold escape mechanisms. The annual species occupy tropical habitats in areas where seasonal drought may be experienced and it is suggested that they have acquired the annual habit as a drought-escape mechanism. The only perennial species in subgenus Scleria in Southern Africa which has annual aerial parts, has evolved additional storage regioni in the swollen culm-bases. This species, S. transvaalensis occurs at higher, more temperate altitudes than other species in the subgenus. The fundamental branching pattern of the inflorescence of all species examined has been shown to be the same. It is postulated that the pattern is modified in two ways, namely, by progressive contraction of all or most ramuli leading to the "glomerate-spicate" type of inflorescence characteristic of subgenus Hypoporum, in which the bracts are reduced, glumiform structures, and, by progressive contraction of some ramuli and progressive elongation of others leading to the "interrupted-paniculate" type of inflorescence characteristic of subgenus Scleria, in which the bracts are foliaceous. It is suggested that the branched glomerate-spicate type of inflorescence is less specialised than the simply glomerate-spicate type, and that in the line with interrupted-paniculate inflorescences, the greater the degree of elongation and the greater the number of elongated ramuli, the more highly specialised the inflorescence. Evidence is put forward that the spikelet of Scleria is a monopodial, that is, racemosely-branched structure, and suggestions that it may be sympodial, refuted. It is postulated that unisexual spikelets in Scleria have been derived by reduction from bisexual (androgynaeceous) spikelets. Unisexual female spikelets are unknown in subgenus Hypoporum which has androgynaeceous spikelets and unisexual male spikelets. It is suggested that the higher the ratio of androgynaeceous to male spikelets in the inflorescence, the less specialised the inflorescence. Unisexual male and functionally unisexual female spikelets occur in subgenus Scleria and, rarely, androgynaeceous spikelets. It is suggested that species which consistently produce some androgynaeceous spikelets are more primitive than those which consistently lack them, and that species whose functionally female spikelets consistently lack any vestigial male parts are more advanced than those which have male rudiments. The hypogynium or "disc" which is present on some achenes is considered to be a new modification of the stipe of the achene and not a vestigial structure, therefore it is postulated that the type of achene found in subgenus Hypoporum which has a trigonous stipe lacking any distal elaboration as an hypogynium is primitive, and that the type of achene found in subgenus Scleria which has an obpyramidal stipe elaborated distally as an hypogynium is derivative. It is suggested that development of the hypogynium has attained its most specialised level in one group of species in which this structure serves as a flotation device. Diagnoses of sections in subgenus Scleria are based partly on differences in morphology of the hypogynium. It has been demonstrated that the cell-walls of the pericarp are silicified, that the process of silification is progressive proceeding from the apex towards the base of the fruit, and that abscission of the fruit takes place when silicification is complete and the vascular supply is severed. The achenes of subgenus Hypoporum have all cells silicified; those of subgenus Scleria have all cells except those of the free flange(s) of the hypogynium silicified. Scanning electron microscopy has revealed details of surface ornamentation of the achenes not previously known, which provide additional diagnostic characters at species level. Attemptsto germinate achenes of Scleria have been unsuccessful : the conditions required, physical and physiological, are not understood. Analysis of anatomical evidence, in particular those characters seen in transverse sections of laminas and culms, confirms that there has been specialisation along two divergent pathways; one which has led to successful occupation of relatively dry, temperate habitats (subgenus Hypoporum), and the other to successful occupation of shaded damp, and open aquatic, subtropical and tropical habitats (subgenus Scleria). One section, Hypoporum, is recognised in subgenus Hypoporum, pending survey of the subgenus on a world basis. Four sections are recognised in subgenus Scleria, namely, Scleria, Acriulus, Schizolepis and Ophryoscleria. Section Scleria may comprise several natural groups, the delimitations of which can not be attempted until a world survey has been made. A map showing world distribution of the genus, and regional distribution maps of Southern African species are provided, also a Table showing the total distribution range of species recorded from Southern Africa. Generic, subgeneric, sectional and species descriptions are provided. Two new species are described. Keys to the Southern African species for use in the herbarium, in the field, and one based on anatomical characters of the laminas are presented. Original descriptions and photographs of type specimens of taxa represented in Southern Africa are included as appendices. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1983.

The distribution of Ricinodendron rautanenii trees is confined to a fairly distinct band across southern Africa. This stretches from South West Africa in the west, through Botswana and Zimbabwe, to Mozambique in the east. These plants are a potential source of both timber and food. In this respect, the fruits and seeds of this species are highly nutritious and the latter, by virtue of their high lipid content, represent an excellent source of oils for both domestic and industrial uses. For these reasons consideration is being given to cultivating this species on a commercial scale. One problem, however, is that the seeds of these plants are dormant and in the first part of this study an attempt was made to establish the cause of this dormancy and how it could be overcome. A thorough investigation of all the possible causes of dormancy revealed that ethylene was the only naturally occurring stimulus that could relieve this condition. Exogenously applied gibberellin (GA3 ) and ethrel were found to be equally as effective as ethylene, but such treatments cannot be regarded as natural. It was also found that all the dormancy breaking treatments were only effective once the endocarp had been removed. This indicated that R. rautanenii seeds had a combined coat imposed-physiological dormancy where ethylene was only able to stimulate germination once the endocarp had been removed. Scarification treatments showed that the endocarp most probably had its effect by restricting embryo enlargement since this structure did not inhibit water uptake or gaseous exchange. Once the ger- mination requirements of these seeds had been established a more detailed investigation was carried out to determine their general sensitivity to ethylene, as well as the actual role this gas played in breaking dormancy. Ricinodendron rautanenii seeds were found to exhibit a high degree of sensitivity to ethylene. The threshold concentration at which a response was obtained was approximately 10¯³ microlitres per litre and this is the lowest yet recorded for any species prior to any additional seed treatments. At concentrations above this, the response was saturated indicating that the seeds are well adapted to the ethylene concentrations most likely to occur in the field. In addition to this, manketti seeds also responded to ethylene after only very brief exposures to the gas and optimum germination was recorded after 30 minutes incubation in an ethylene saturated atmosphere. The temperature range over which an optimum response to this phytohormone was obtained was found to be between 25 and 35°C. One of the most striking features regarding the sensitivity of these seeds was the apparent ability of dry and partially imbibed seeds to perceive the dormancy breaking stimulus. Furthermore, once treated, the seeds retained the dormancy breaking effect of ethylene even when subjected to almost complete re-dehydration. In this instance, 50 per cent germination was recorded for ethylene treated seeds which had lost approximately 97 per cent of their moisture content between dormancy breaking and re-incubation. It was thus concluded that, not only could Ricinodendron rautanenii seeds respond to very low ethylene concentrations but could probably also retain the effects of this gas during adverse environmental conditions. The effects of imbibition and dormancy breaking were followed separately at the ultrastructural and biochemical level. The ultrastructure of dry embryonic axes of these seeds was characterized by massive stores of food reserves in the form of lipid and protein. Upon imbibition the number and size of spherosomes decreased and protein and globoid hydrolysis was clearly evident. Polysomes and microbodies (including mitochondria) were also visible prior to dormancy breaking but there was no evidence of any endoplasmic reticulum or dictyosomes. Imbibition also resulted in the expans ion of the nuclei and there were indications of an increase in the granular content of the associated nucleoli. The number of nucleolar vacuoles, however, remained unchanged. These features indicated that nuclear activity had commenced albeit limited. The ultrastructure ·of untreated seeds which were maintained in the imbibed state for an extended period of time (six days) was also examined. Cells of the embryonic axes of these seeds showed no further changes with regard to their nuclei and protein hydrolysis appeared to have ceased. At this time spherosomes resembled those in freshly imbibed tissue in terms of their size and numbers, suggesting that the lipid reserves had been resynthesized. No immediate ultrastructural changes were observed after ethylene treatments. However, 24 and 48 hours after dormancy breaking further expansion of the nuclei was noted. At the same time the nucleolar vacuoles disappeared and the granular content of this region increased markedly. This suggested that an increase in the synthesis of various RNA fractions was taking place. Vigorous protein hydrolysis was also observed after the ethylene treatment whereas spherosome numbers increased. Three days after the dormancy breaking treatment, the first signs of germination were visible. Externally this was characterized by a splitting of the testa in the region of the radicle. At this time, endoplasmic reticulum and dictyosomes were still not visible but from this point onwards the ultrastructural changes observed were typical of those recorded during the germination of other species. Thus, no single ultrastructural feature could be associated with the breaking of dormancy and the most notable changes which occurred during this period took place in the nucleus. Biochemical changes occurring during imbibition resulted in an overall decrease in the levels of extractable food reserves present in the embryonic axes. During this period, lipid levels were found to decrease by 44 per cent, protein levels by 12 per cent, sucrose levels by 68 per cent and glucose, fructose and starch levels by 100 per cent. These levels were found to return to their original values when seeds were incubated under moist conditions in the absence of ethylene for extended periods of time. Ethylene treatments, on the other hand caused a further, marked decrease in sucrose levels, whereas protein and lipid levels increased. Hydrolysis of the endosperm reserves commenced three days after the application of ethylene and this was characterized by a decrease in lipid levels and an overall increase in soluble carbohydrates. The timing of this event suggested that the endosperm was not involved in the actual process of dormancy breaking. The importance of protein synthesis in dormancy breaking was also investigated. It was found that seeds incubated with a protein synthesis inhibitor, cycloheximide, failed to germinate, confirming the view that protein synthesis is an essential pre-requisite for germination. Inhibition of RNA synthesis with actinomycin D, on the other hand, did not prevent germination. This suggested that the materials necessary for early protein synthesis were already present in the dry seeds. Actual measurements of protein synthesis showed that this process took place in the embryonic axis, cotyledons and endosperm of seeds imbibed for as little as two hours. Protein synthetic abilities increased considerably in most instances after 48 hours imbibition but then decreased upon application of ethylene. At the same time, however, a marked increase in the uptake of 14C-Ieucine was noted in ethylene treated axes. This may indirectly reflect an effect of ethylene on membrane permeability. Protein synthesis in cycloheximide and actinomycin D treated embryonic axes was also measured. No consistent trends were evident but it was found that after ethylene treatments, protein synthesis was generally lowest in those seeds which were destined to germinate. In addition, these seeds also exhibited the greatest uptake of [14]C-Ieucine. Ricinodendron rautanenii seeds incubated with compounds known to stimulate the pentose phosphate pathway failed to germinate. This indicated that dormancy in this species was probably not the result of a block in alternate respiration. The possible involvement of endogenous phytohormones in the overall process of dormancy breaking was also in- vestigated. In this regard, the role of gibberellic acid appeared to be enigmatic. This is based on the observation that applied gibberellins could stimulate germination whereas inhibitors of endogenous gibberellin synthesis applied to ethylene treated seeds had no effect. It was concluded from this that the effects of ethylene are not mediated via an enhancement of endogenous gibberellin synthesis. A preliminary investigation carried out on the endogenous cytokinins showed that this hormone was absent from dry and imbibed seeds. A transient increase in zeatin levels was observed 24 hours after the ethylene treatment. A similar transient increase was noted in non-induced seeds maintained under moist conditions for six days. In this latter instance, however, the peak co-chromatographed with the biologically less active cytokinin, zeatin glucoside. A basal level of endogenous ethylene production was recorded in all imbibed Ricinodendron rautanenii seeds. Ethrel, ethylene and gibberellin treatments caused an initial, transient increase in this ethylene production after which no further significant changes were recorded. It is suggested that dormancy breaking in this species is not related to enhanced endogenous ethylene synthesis. The results of the biochemical and ultrastructural studies are discussed in relation to what is known regarding features associated with dormancy and its removal and on the known effects of ethylene on seed tissues. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1982.