The present-day cycads represent the diverse, modified remnants of a much larger group of gymnosperms which flourished in the Mesozoic Era. The approximately 148 surviving species of the Cycadales are sparsely distributed through tropical and sub-tropical floras in a variety of habitats. About one-half of the extant taxa are considered endangered, vulnerable or rare and, because of their scarcity and decorative appeal, have attracted much public interest. Their slow growth rate, the paucity of viable seeds and limited potential for vegetative reproduction severely limit both the natural regeneration and the controlled propagation of cycads. Over the past 40 years, various attempts have been made to establish in v~o systems for cycad culture but none has been successful in establishing a functional protocol for the artificial propagation of these plants. The author has made renewed attempts to establish in vitro cultures from a range of haploid and diploid tissues from South African Encephalartos and Stangeria species. Callus proliferation was readily obtained from most explant sources of most species using a variety of media. Addition of the growth factors 2,4-dichlorophenoxyacetic acid and kinetin in the 10[-7] to 10[-6]M range was beneficial but not essential. Culture vessels which allowed relatively free gaseous interchange were advantageous and dark conditions were marginally better than constant light. Explants from cycad taxa which are mesic in habit gave a more rapid response than similar explants from xeric plants. Attempts to induce any form of differentiation other than, or after, callus formation were unsuccessful in all Encephalartos cultures, but two forms of morphogenesis were obtained from Stangeria-derived material. Megagametophytic tissue occasionally developed spherical outgrowths analogous to coralloid root primordia. More significantly, primary root cultures after callus formation, subculture and transfer to a light environment, regularly gave rise to meristematic zones and subsequent leaf emergence. This is the first recorded case of in vitro morphogenesis of a South African cycad. The order Cycadales shows several distinctive phytochemical features, principally the presence of the unique methylazoxymethanol glycoside toxins and a-amino-s-methylaminopropionic acid together with some unusual phenolic compounds, flavanoids, carotenoids and cyclitols. Stangeria differs from other cycads in at least two phytochemical aspects; the absence of biflavonoids in the leaves and the absence of rhamnose and methyl rhamnose in the hydrolysed mucilages. These diffe.rences may indicate broader physiological differences which would in turn explain the observed differences in morphogenetic competence of tissues from Stangeria and Encephalartos. Analyses of various tissues from these and other cycad taxa were performed with respect to moisture, protein, enzyme, toxin and hydrocarbon content. Significant differences, both between organs and between taxa, were noted. The results of peroxidase analyses were particularly important in that high levels of this enzyme correlate with the rapidity of callus formation in vitro. Furthermore, a sharp increase in peroxidase activity signals the onset of callogenesis in Stangeria megagametophyte cultures. An important incidental aspect of the phytochemical analyses is that of potential value of these data to the taxonomist. In particular, the leaf wax hydrocarbon profiles appear to be species-specific and are ideally suited to processing by numerical taxonomy computer programmes. It is anticipated that extension of this work will make a significant contribution to the resolution of existing problems in cycad taxonomy and, additionally, provide a means to construct phylogenetic sequences in the order. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1988.

Adventitious rooting in stem cuttings of Eucalyptus grandis Hill ex Maid. was thought to be influenced by a putative inhibitor. In previous studies it has been usual to infer the presence of putative rooting inhibitors and promoters from the mung bean bioassay, but the possibility was raised that treatment responses in this assay could be mediated more by the concentration of the treatment solution than by the chemical identity of the solute. This appeared to be so: several solutes, including hydrochloric acid and common salt, were found to promote the rooting of mung bean cuttings when present in the treatment solution at an apparently injurous concentration. The concept of promoters and inhibitors of adventitious rooting, as constituted at present, was considered to be an unfavourable approach for further studies. Stem cuttings must contain a morphogen, broadly defined, which operates the 'switch' from stem to adventitious root. The leaves and buds of E.grandis stem cuttings did not appear to be sole sources of a morphogen (as is often assumed), but nevertheless the activity of the leaves and buds was good for rooting. This activity was reflected in the pattern of root emergence. A slight preponderance emerged from the leaf trace sectors of the stem, suggesting that the leaves and buds cause a morphogen (of unknown origin) to circulate in the cutting. The existence of a vascular morphogen was confirmed and it proved to be very mobile in the stem, suggesting that it is well distributed circumferentially at the base of the cutting rather than confined to the leaf trace sectors. It appeared to be super-abundant at the base of easy-to-root cuttings, but it was not possible to tell to what extent the morphogen was rendered accessible to the sites where roots initiate. In general, the rate of efflux from the transporting tissues, the rate of attenuation of the morphogen after efflux, and the number of potential sites for root initiation must interact on a small scale to determine rooting ability. The relative prominence of these groups of factors would be expected to vary with circumstances, for example at different locations within a single stem cutting, so the traditional concept of a limiting morphogen ('rhizocaline') is unhelpful in its simplest form. Nevertheless, the rhizocaline concept provides a starting point towards a more comprehensive view of adventitious rooting, which is required in order to predict and improve rooting ability. This view remains a remote objective because many of the factors which could be important have recieved very little attention and will be difficult to elucidate. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1988.

Aspects of the physical and chemical environment likely to influence phytoplankton productivity were investigated in Lake Midmar, a shallow (mean depth 11.4m), oligotrophic impoundment, over a three year period to evaluate the hypothesis that "the fundamental process regulating the functioning of a shallow lake is vertical mixing." Energy exchange at the lake surface was similar to that reported for other lakes. The principal components of the energy balance (net incoming radiation and latent heat loss) and heat content of the lake varied seasonally. However, day-to-day variation in local weather, particularly the incidence of cloud cover, masked these seasonal trends and contributed to the unusual pattern of almost constant sensible heat loss throughout the year. Consequently, heat storage was highly variable, particularly in early summer (September-December). The combination of day-to-day variation in heat storage, the pattern of heat loss, wind stress and the synergistic interaction between these components together contributed to the observed pattern of weak summer stratification (absence of vertical partitioning into an epi-, meta- and hypolimnion) and efficient heat transfer within the water column. The occurence of low Wedderburn numbers ( W < 1) on several occasions during summer (September - February) resulted in Midmar being classified as a regime 2 lake (sensu Spigel and Imberger,1980) and the thermal structure as discontinuous polymictic (sensu Lewis,1983 a). Under conditions of 'normal' river flow (1980-81) phosphorus associated with river suspended solid loads, even at times of peak loading in late summer, had little immediate influence on the total phosphorus content of the water column or phytoplankton productivity. Internal phosphorus loading, resulting from sediment resuspension and transfer of phosphorus from sediment pore water to the overlying water, was identified as the principal source of bioavailable phosphorus. The wind-induced circulation - sediment interaction also exerted a strong influence on the underwater light climate. Inorganic suspended particulate material was the principal factor regulating the attenuation of photosynthetically active radiation (PAR). Red light being the most penetrating component of the PAR spectral range throughout the study period . The hypothesis that 'internal", autochthonous processes and not external, allochthonous processes were responsible for regulating phosphorus dynamics and PAR attenuation" was confirmed during the drought (1982-83). As lake levels decreased the increased interaction between wind- induced circulation and the deeper sediments led to increased PAR attenuation and total phosphorus concentrations in the water column. The range of turbulent conditions arising from variation in the magnitude and frequency of wind- induced circulation created a temporally variable environment characterised by low values of the ratio Z[eu]:Z[m] rapidly changing light levels to which algal cells would be exposed in any day (a result of the turbid, turbulent nature of the environment) and nutrient patchiness (resulting from variation in internal phosphorus loading). The subsequent variation in the physiological state of the phytoplankton at the time of sampling resulted in estimates of ΣA, P[max] and the physiological indices, I[K], P[e] and assimilation number, being very variable from one sampling occasion to the next. This variation in phytoplankton productivity and physiological state at the time of sampling was considered to be responsible for the general absence of any correlation between ΣA, the physiological indices and temperature as well as the observed variation between the real values of ΣA and those predicted using Talling's model. Although the increased wind-induced circulation - deeper sediment interaction during the 1982-83 drought caused changes in the underwater light climate (as increased PAR attenuation and shallower euphotic zones) these changes had little effect on values of I[K], and P[e]. However, from the increase in values of ΣA, phytoplankton standing crops and assimilation numbers recorded in 1982-83 it was concluded that phytoplankton productivity in Lake Midmar was nutrient and not light-limited. The role of vertical mixing as a factor influencing temporal changes in phytoplankton species composition is examined in the general discussion. Two properties of the mixing regime are considered to be important, i.e. the energy associated with a particular mixing event and the frequency of high energy mixing events. The concept of disturbance sensu White and Pickett (1985) was found to be useful in distinguishing 'normal' low energy advective and vertical mixing involving only the surface waters from disturbance, high energy vertical mixing involving most or all of the water column which is capable of modifying existing environmental gradients. Based on the frequency of wind-induced disturbance a continuum can be shown ranging from deep stratified lakes, where disturbance as changes in mixing regime associated with the onset and breakdown of stratification is infrequent, seasonal and predictable from one year to the next, to very shallow lakes, where disturbance as extensive vertical mixing is more frequent, aseasonal and unpredictable. Shallow impoundments, e.g. Lake Midmar, occupy an intermediate position between the two extremes of the continuum. The exact location of a particular shallow lake being determined by site-specific properties of the energy exchange-wind stress interaction and resultant mixing regime. It is considered that the failure to recognise the intrinsic variation between shallow impoundments and the importance of site-specific differences in determining the importance of wind-induced vertical mixing in the functioning of shallow impoundments led to the earlier classification of South African shallow impoundments as warm monomictic systems by Walmsley and Butty (1980). Furthermore, this property of shallow lakes (i .e. the sitespecific differences in the energy exchange-wind stress interaction) probably accounts for the limited success with which general lake models have been applied in shallow lakes. Disturbance has not been recognised as a source of temporal and spatial heterogeneity in the physical and chemical environments of lakes because of the failure of existing models to distinguish between disturbance and perturbation and their roles in initiating changes in phytoplankton species composition. Based on the results of this study a revision of Reynolds's model describing temporal changes in phytoplankton species composition which incorporates both disturbance and perturbation is proposed. The results of this study therefore confirmed the original hypothesis that "the fundamental process regulating the functioning of a shallow lake is vertical mixing" with summer thermal structure, the attenuation of downwelling PAR and phosphorus dynamics all being directly influenced by wind-induced vertical mixing. The resultant temporally variable environment also influenced the physiological state of the phytoplankton and estimates of primary productivity, and is considered to exert a strong indirect influence on phytoplankton seasonal periodicity in this shallow, oligotrophic, turbulent impoundment. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1988.

Abstract cannot be copied from pdf document. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1987.

Unable to copy from pdf. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1985.

In this ethnopharmacological study to isolate, purify, identify and test crude and isolated compounds from organic and aqueous extracts from stem and leaves of Protorhus longifolia and Sclerocarya birrea, stem bark of Hibiscus cannabinus and Heteropyxis natalensis, leaves of Acokanthera venenata, Carissa marcrocarpa and Syzygium cordatum, seeds of Chiononthus foveolatus and calyces of Hibiscus sabdariffa were tested against seven pathogenic microorganisms which included six bacterial species [Klebsiella pneumoniae (ATCC 12265), Bacillus cereus (ATCC 11778), Salmonella typhimurium (ATCC 13311), Pseudomonas aeruginosa (ATCC 27853), Escherichia coli (ATCC 35219), Staphylococcus aureus (ATCC 29213)) and fungal yeast Candida albicans (ATCC 10231)]. Both organic and aqueous extracts from these medicinal plants exhibited antimicrobial properties against one or more mlcroorgamsms. The extracts of stem bark and leaves were tested for antimicrobial properties. Crude extracts that showed the highest activity were analysed through chromatographic and spectroscopic techniques to isolate, purify and characterise their active components. The highly active antimicrobial extracts were further tested for antimicrobial activity. Chromatographic (TLC and CC) spectroscopic (IR, 13C, 1HNMR) analyses of Syzygium cordatum leaf extract in ethyl acetate revealed the presence of C-30 triterpenes, ursolic (3B-hydroxyurs-12-en-28-oic acid) (UA) and oleanolic (3-hydroxylean-12-en-28-oic acid) (OA) acids; a mixture of methyl maslinate (2a, 3B-dihydroxyolean-12-en-28-oic acid methyl ester) (MM) and methyl corosolate (MC). Analyses of Protorhus longifolia leaf extract in hexane and ethylacetate revealed the presence of the alkaloid lupeol (lup-20(29)-en-3pB-ol), lupenone [lup - 20 (29) - en - 3 - one or lup - 20 ( 30 ) - en - 3 - one], lupinine (octahydro-2H-quinolizine-lmethanol), lupulon (3 ,5-dihydroxy-2,6,6-tris(3-methyl-2-butenyl)-4-(3-methy1-1-oxobutyl)-2,4-yclohexadien-1-one) or (3,5-dihdroxy-4-isovaleryl-2,6,6-tris(3-methyl-2-butenyl)-2, 4-cyclohexadien-1-one) and luteolin [(2-(3, 4-dihydroxyphenyl)-5, 7-dihydroxy-4H -1-benzopyran-4-one), 3',4', 5,7 -tetrahydroxyflavone or 5,7,3' 4' - tetrahydroxyflavone] and other compounds to be characterised in future studies. Sclerocarya birrea bark extract in methanol was found to contain mixtures of compounds that could not be separated due to solvent complications. Heteropyxis natalensis stem bark in ethyl acetate gave betunilic acid (3B-hydroxy-20(29)-lupaene- 28-oic acid) as a major compound. / Thesis (M.Sc.)-University of KwaZulu-Natal, 2006.

A review of the literature pertaining to the sites of synthesis, distribution and metabolism of cytokinins, established that there was a need to investigate the quantitative and qualitative changes in cytokinin levels during the growth cycle of a whole plant. An annual legume, Lupinus albus L. (the white lupin), was selected as the experimental plant for such a study. The levels of cytokinin activity in the root exudate, leaves and terminal (primary) apices of mature plants were examined between 5 and 17 weeks after planting. The results indicated that the total level of activity in the root exudate of a single plant is much greater than that which accumulates in the leaves and apices up to the time of flowering. This was considered to be indicative of rapid utilization of cytokinins in the actively growing shoot. It was also established that, after flowering, the level of activity in the terminal apices increases markedly, while that in the root exudate decreases. The latter finding was examined more closely in the next experiment, during the course of which cytokinin levels in the root exudate, leaves, fruits and fruit sap were determined at 2 weekly intervals after flowering. As in the previous experiment, the results showed that, although there may be a slight increase in the amount of activity in the root exudate, this activity was insufficiently high to account for the levels of cytokinin which accumulate in the fruiting apices. Cytokinin activity was however detected in the sap passing into the fruits (largely phloem sap), thereby indicating that at least some of the cytokinins detected in both pod wall and seed extracts could have originated in other parts of the plant. Embryonic development was followed at the gross morphological, anatomical and ultrastructural levels, and estimates were made of the cytokinin levels in the embryos and adjacent tissues. The results indicated that the cytokinin levels in the flowers, and young fruits, were low, but gradually increased with time. At 2 weeks after anthesis the level of activity in the pod wall was higher than that in the individual seeds. By 6 weeks, however, the activity in each seed was in excess of that recorded in the pod wall. Decreasing levels of activity in the seeds, and increasing levels in the pod wall, reversed this trend at later developmental stages. The level of activity recorded in the maturing embryo was low, while in the adjacent tissues it was high. This was especially noticeable at 6 weeks after anthesis when the cytokinin activity in the endosperm reached a high level. It would appear that these cytokinins facilitate nutrient mobilization to the tissues surrounding the embryo, and that they are possibly utilized in order to promote certain growth processes taking place in the embryonic cells during development. The cytokinin activity in the mature embryo was low, but increased slightly in the cotyledons, radicles and young shoots during germination and seedling establishment. The cytokinins present in all white lupin extracts had chromatographic properties, on paper and/or Sephadex LH-20, similar to the naturally occurring cytokinins zeatin and zeatin riboside and their glucosylated or phosphorylated derivatives. Mass spectrometric-analysis of the compound co-eluting with zeatin showed that this cytokinin was present in white lupin extracts, while analysis of the peak co-eluting with zeatin riboside indicated that the cytokinin at this elution volume was an adenine derivative. The possible presence of dihydroderivatives of these cytokinins was also indicated. The results did not exclude the possible presence of other cytokinin-like compounds. The significance of qualitative as well as quantitative changes in cytokinin activity were assessed. It is concluded thatcytokinins do not accumulate at excessively high levels in actively growing tissues, unless these tissues function as a transitory store for nutrients, as for example the endosperm, testa and pod wall. Cytokinins are probably involved in the control of a number of growth processes of which nutrient mobilization may be of considerable importance to the plant. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1978.

The metabolism of carbohydrates in guayule is a subject which has not been considered with respect to its role in cis-polyisoprene synthesis, It has been suggested that acetate or sucrose act as the distal, and isopentenylpyrophosphate as the immediate precursor of the isoprenoid biosynthetic pathway. Application of radioactive precursors to the leaves of guayule plants in Winter and Summer showed that the fate of the carbohydrate depends on the chemical structure of the carbohydrate and the time of application. [[14]C] Sucrose was incorporated into the acetone (resin) fraction during the Summer and petroleum ether (rubber) fraction during the Winter. The amount of radioactivity that was translocated in Winter and Summer was similar. The loss of leaves during Winter reduced the area for photosynthesis, while the loss of carbon from the leaves during Summer, probably due to photorespiration, decreased the amount of available photosynthates. These two phenomena did not disadvantage the plant as far as the allocation of carbon was concerned. No plant components were acting as sinks during the Winter. The pith of the crown area incorporated the most radioactivity in Summer. [[14]C] Fructose was more readily translocated than [[14]C] sucrose during a 12 hour experiment. When fructose was applied and plants were left for 48 hours, more radioactivity was translocated to the stems and roots during the Summer. The [[14]C] from fructose was incorporated into the acetone (resins) rather than the petroleum ether (rubber) fraction in Winter therefore apparently having a different fate to [[14]C] sucrose. The principal reserve carbohydrates in guayule are fructans. Two types of fructans were detected and are referred to as water-soluble or ethanol-soluble fructans. The ethanol-soluble fructan polymers apparently played an active role in metabolism of guayule and showed cyclic patterns of accumulation. The water-soluble fructans seem to be true reserve carbohydrates, depolymerizing when the carbon supply decreased at the end of Winter, and the demand for carbon increased at the inception of bud break. Fructans provide carbon for budbreak and exposure of plants to longer days and higher temperatures did not seem to alter this role. It is proposed that fructans are providing carbon for budbreak and renewed growth and are utilized for flowering when required. Starch production occurs during the warmer months in the leaves and young stems. Starch is synthesized from the immediate photosynthetic supply and it is this source of carbon which is utilized for the synthesis of cis-polyisoprene (rubber). Sucrose in the cytosol is sequestered for cis-polyisoprene synthesis while fructose, which can enter the plastid, is providing carbon for the synthesis of isoprenoids. Compartmentation of resin and rubber production ensures that the supply of carbon is adequate for both processes. As cis-polyisoprene synthesis occurs at a time when the plant is not disadvantaged by insufficient carbon , induction of rubber transferase enzymes would not depend on excess substrate, but would use a more reliable cue like temperature or daylength. Any attempt therefore to increase the carbon supply in guayule during the winter months would not necessarily lead to partitioning into cis-polyisoprene, but may be stored as fructan to ensure that, at bud break, the plant has an adequate and utilizable carbon supply. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1991.

Solanum mauritianum Scop. is rated the worst invader species in pine plantations throughout the Republic of South Africa. Control is costly and apparently ineffectual since the species is spreading in pine plantations at a rate of 16 % per annum. This is due to the high reproductive potential of the species. S. mauritianum produces fruits throughout the year. Fruit and seed yield is related to tree size. S. mauritianum produced approximately 7.2 million viable seeds per hectare during 20 months when growing under conditions unfavourable for growth. Seeds are efficiently dispersed by animals and birds. Although high seed or seedling mortality occurs, the initial prolific seed production and efficient dispersal ensures the rapid spread of this species in South Africa. Surviving seeds form the source for both further encroachment and reinfestation of areas in which S. mauritianum has been controlled. S. mauritianum seeds require the presence of both light and alternating temperatures for optimum germination. Transfer of seeds from unfavourable to optimum conditions or the application of gibberellic acid (GA [3]) can promote high germination percentages. However, the germination requirements of S. mauritianum are highly variable. Germination is influenced by site, season and year of seed shed. Seeds varied in terms of primary dormancy; conditional dormancy; the response to transfer from unfavourable to favourable conditions; the response to application of GA[3]; and the occurrence of secondary dormancy. Germination requirements of seeds were also influenced by site, duration and depth of burial. All these factors contribute to a sporadic seedling emergence over a prolonged period, which results in current control operations being both costly and ineffective. Alternative control methods were therefore considered. These included the application of herbicides or heat to kill seeds, application of various gro~th regulators to stimulate germination, and the chemical extraction of alkaloids from fruits and seeds for use in the pharmaceutical industry. Two alkaloids (solasodine and a new molecule) were extracted from green bugweed fruits growing under unfavourable conditions. Although levels of solasodine extracted were very low compared with those from commercially grown species of this genus, extraction of the second alkaloid raised the potential of the species for utilization purposes. Utilization of the reproductive propagules could reduce the continual dispersal of seeds and thereby contribute to long-term control of this species. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1990.

Abstract viewable in PDF document. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1985.