Thèse--Geneva. / "Thèse no. 1250." Bibliography: p. 163-188.

The work on Spiraea in vitro shoot cultures was done to determine the feasibility of using light quality to modify endogenous phytohormone balances to decrease apical dominance. Such an effect would enable a reduction in the high levels of exogenous cytokinin benzyladenine (BA) applied in culture and thus reduce potential side-effects. The Spiraea in vitro light quality response was characterized by examining the effects of different light wavelengths on growth. A mixture of red/FR induced rates of shoot proliferation with 0.25 mg/1 BA that were as high as rates obtained under white light with 0.5 mg/1 BA. Shoot quality, as determined by the proportion of shoots 1 cm or longer (useful shoots), was highest under red/FR light. The lowest shoot proliferation rate was observed under blue light. When light wavelengths intermediate between blue and red light (green, yellow, and orange) were applied to explants only minor growth modifications occurred. Green light did not inhibit shoot initiation but inhibited shoot elongation at the 0.5 mg/1 BA level. The efficacy of the light source-filter combinations in the first experiment was studied in two further experiments. With the three light sources (tungsten filament, fluorescent, and metal halide) together with a blue filter, results supported the putative blue light inhibitory effect suggested in the first light quality experiment. Under the red filter, the tungsten filament source induced the highest shoot number means at both BA levels used (0.25 and 0.5 mg/1). Two factors may have contributed to the red/FR effect observed in the first experiment; the time under an incubation light regime before transfer to the treatment regime, and the photon fluence rate of each regime. In the subsequent study to examine these factors, shoot initiation was optimized at the lower BA levels of 0.25 and 0.4 mg/1 when cultures under low fluence red/FR were transferred after four weeks to white light of a higher fluence for one more week. Glyphosate, a known promoter of IAA oxidation, was used to investigate the presumed effect of lowered IAA-cytokinin interactions. Two types of responses to glyphosate occurred, each one dependent on the glyphosate concentration. At the lower glyphosate level (0.087 mg/1), cultures under both light regimes with 0.25 mg/1 of BA, showed a strong inhibition of shoot initiation. This inhibitory effect was overcome in cultures with 0.5 mg/1 of BA and an overall stimulatory response occurred as shoot initiation rates were as much as four-fold higher than in the previous experiments. For both BA levels, changes in shoot number were greater under white light than under red/FR. At the higher glyphosate level (0.2 67 mg/1), the shoot initiation rates were greater than glyphosate-free controls for both BA levels under white light although under red/FR the rates were virtually unchanged from controls. The glyphosate effect investigated for Spiraea cultures appears to be influenced by the levels of the cytokinin BA resulting in pleiotropic effects which depend on the specific concentrations of each component. / Land and Food Systems, Faculty of / Graduate

The ecology, species distribution, and population structure of Armillaria was investigated in the forests of Massachusetts. From 64 plots at 16 sites, 640 isolates of Armillaria were collected from six forest types (northern hardwoods, mixed oak, pitch pine, white pine, white pine/mixed oak, and eastern hemlock). Armillaria gallica proved to be the most abundant species, making up 316/640 (52%) of all isolations. This was followed by A. solidipes (219/640; 34%), A. mellea (46/640; 7%), A. calvescens (36/640; 6%), A. gemina (16/640; 3%), and A. sinapina (7/640; 1%). Armillaria gallica was routinely encountered causing significant decay of the lower bole on living hardwood hosts, especially oaks. The population structure of 153 isolates of A. gallica collected from mixed oak forests was investigated using amplified fragment length polymorphisms (AFLPs). From a total sampling area of 4.51 ha, 38 AFLP genotypes were discovered, yielding a figure of eight genets per hectare with the average A. gallica genet occupying 0.13 ha. When the effects of hydrolyzable tannins on in vitro growth were compared between A. calvescens and A. gallica, it was A. gallica that appeared better at oxidizing and metabolizing commercial tannins (tannic acid and gallic acid) along with black oak root bark extracts. This was determined through measurements of colony area and dry biomass, and suggests that A. gallica may be a better adapted pathogen of oak. In order to more accurately distinguish between isolates of A. calvescens and A. gallica, a three-gene phylogeny was reconstructed, using partial sequences of the elongation factor 1-alpha (tef1), RNA polymerase II (rpb2) and nuclear large subunit (nLSU) genes. After comparing 12 isolates each of A. calvescens and A. gallica that originated from across northeastern North America, only the tef1 gene could accurately distinguish these two species. Five single nucleotide polymorphisms were present between the two species and maximum likelihood and maximum parsimony methods grouped A. calvescens and A. gallica into monophyletic clades.

Iron is one of the most important micronutrients used by living organisms. Iron is frequently a limiting nutrient for plant growth, and plants are a major source of iron for human nutrition. The most prominent symptom of iron deficiency in plants is interveinal chlorosis, or yellowing between the veins, which appears first in the youngest leaves. Iron deficiency anemia (IDA) is the number one human nutritional deficiency worldwide. In order to solve the problem of iron deficiency, it is desirable to breed plants that have increased iron in those parts that are consumed by humans. To do this, we must first understand the molecular basis of Fe uptake, transport, and storage in plants. In soil, iron is quickly oxidized to Fe(III), and Fe(III) is relatively insoluble, thus difficult for plants to obtain. Our lab has been working on metal ion homeostasis mechanisms in plants and the ultimate goal of our research is to understand the mechanisms by which plants maintain the correct levels of iron, zinc and copper in each cell and tissue. The Yellow Stripe-like (YSL) family of proteins has been identified based on sequence similarity to maize Yellow stripe 1 (YS1). YS1 transports Fe(III) that is complexed by phytosiderophores (PS), strong Fe(III) chelators of the mugineic acid family of compounds. Non-grass species of plants neither make nor use PS, yet YSL family members are found in non-grass species including Arabidopsis thaliana. YSLs in non-grasses have been hypothesized to transport metals that are complexed by nicotianamine (NA), an iron chelator that is structurally similar to PS and which is found in all higher plants. In this dissertation, Arabidopsis YSL1 and YSL3 are demonstrated to be important in iron transport and also responsible for loading Fe, Cu, and Zn from leaves into seeds. Arabidopsis YSL4 and YSL6 are demonstrated to be involved in iron transport and metal mobilization into seeds. The transport function of Arabidopsis YSL1 and YSL2 are shown be partially overlapping to the function of Arabidopsis YSL3 in vegetative structures, but distinct in reproductive organs. Arabidopsis YSL3 and YSL6 are shown to have distinct functions in planta.

Little is known about the demographics of the genus Acacia in Africa, despite its prominence and the economic and environmental importance of this group. The demographics and species composition of stands of four different Acacia species was investigated in the Hluhluwe-Umfolozi Game Reserve in northern Kwazulu-Natal in order to determine whether stands were self-replacing, or whether other Acacia species were invading them. Soil and stand density as well as the density and composition of the grass layer were investigated in order to determine whether any of these affected Acacia demography and species composition. In three out of four cases, the species whose large size class dominated the stand (known as the "stand species") was found to have a strongly bimodal size class distribution, skewed primarily towards the large size class and secondarily towards the small size class. Other Acacia species in the stands, with few or no large individuals present ("nonstand species") tended to have unimodal size class distributions, skewed primarily towards the small size class and secondarily towards the medium size class. Based on the proportion of small to large individuals, non-stand species are more likely to increase in overall numbers in future, suggesting that the species composition of the stands may be in a state of flux. Few relationships were found between stand density, grass density, grass composition and numbers of small and medium acacias. This could be as a result of differentiation between Acacia species, meaning that they cannot be analysed collectively. Furthermore, sample sizes of individual species may have been too small to analyse individually. Alternatively, it could mean that none of these factors have a significant effect on one another and that other explanations need to be found for the demographics of this genus.

Pollen grains serve a very important role in the life cycle of flowering plants, in that they are involved in the transmission of inherited characteristicsfrom generation to generation. Because of their small size the study of pollen grains has been necessarily associated with the development of the microscope. Not until the middle of the seventeenth century, when Hooke gave the world the compound microscope, was an instrument available with sufficient power to adequately reveal the shapes of pollen grains. However , two of Hooke's contemporaries, Malpighi and Grew, who used a simple microscope , are generally recognized as the co-founders of pollen grain morphology.

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Thesis (MTech (Agriculture))--Cape Peninsula University Of Technology, 2016. / Bambara groundnut (Vigna subterranea), a dicotyledonous plant is a legume which has a potential to contribute to food security and nutrition. Protoplasts are naked plant cells lacking cell walls. Viable protoplasts are potentially totipotent. Therefore, when given the correct stimuli, each protoplast is capable, theoretically, of regenerating a new wall and undergoing repeated mitotic division to produce daughter cells from which fertile plants may be regenerated through the tissue culture process. Protoplast systems are valuable and versatile cell based systems that are useful in observing cellular processes and activities. In this study, the isolation of protoplast from the leaves of Bambara groundnut plant was extensively optimised. The factors affecting protoplast isolation considered in this study were ages of plant material, mannitol concentration, combinations and concentrations of enzymes and duration of incubation. Effects of ages of Bambara groundnut plant (4, 6, 8, 10 weeks), molarities of mannitol (0.4 M, 0.5 M. 0.6 M and 0.7 M), concentration and combination of enzymes (1%, 2% and 4% cellulase, 0.5% and 1% macerozyme and, 0.5% and 1% pectinase) at different incubation duration (4, 18, 24, 42 hours) were investigated. Overall, it can be deduced from this study that the optimal protoplast yield (4.6 ± 0.14×105ml-1/gFW) and viability (86.5 ± 2.12%) were achieved by digesting the leaves of four week old Bambara groundnut plant with 2% cellulase and 0.5 % macerozyme with 0.5M mannitol for 18 hours. Freshly isolated protoplasts were then cultured at different densities of 1 × 104 - 2 ×106 protoplasts/ml using MS in three different culture (Liquid, agar and agarose bead) methods. First cell division was observed only in liquid medium. With several attempts, no division was achieved in the agar and agarose bead methods, division also did not progress in the liquid medium and hence, plant regeneration from Bambara groundnut protoplasts could not be achieved in this study. Consequently, a further study is underway to compare the proteomic profiles of freshly isolated protoplasts and cultured protoplasts in order to gain insights into the expression of proteins that could perhaps be contributing to the difficulty in regenerating Bambara groundnut plant through protoplast technology. The present study is novel because it is the first study to optimise the various factors that could affect protoplast isolation from the leaves of Bambara groundnut and thus developed an efficient protocol for protoplasts isolation from leaves of Bambara groundnut for cell manipulation studies.