<p> Over the past century, changes in farming practices have resulted in an enormous increase in agricultural productivity. Substantial gains in crop yields were due to several factors, including the use of nitrogen fertilizers and pesticides (Youngquist, 1999). These chemicals are primarily derived from fossil fuels, such as petroleum and natural gas. Considering these are both finite resources, there is a need to develop alternative technologies that boost crop productivity in a sustainable way. Recent studies have proposed the use of endophytes to promote plant growth and increase yields. One specific endophyte, <i>Enterobacter</i> sp. 638, has been shown to enhance plant growth in a variety of hosts. <i>E.</i> 638 produces plant hormones which result in increased biomass (Taghavi <i>et al.,</i> 2011). This study measures the effects of inoculation with <i>E.</i> 638 on growth and gene expression in tomato (<i>Solanum lycopersicum </i>). Two factors, inoculation and stress, were examined for their effects on time to flower, time to first produce fruit and first ripening event, as well as total mass of fruit and vegetative tissue. Stressed conditions were simulated by growing tomato plants in small (19 L) pots in a greenhouse, while unstressed plants were placed outside in larger (&sim;57 L) pots to minimize restriction of root growth and maintain a more natural environment.</p><p> Furthermore, this study used qPCR to measure the relative expression of genes involved in auxin transport, cytokinin signaling, ethylene signaling and cell wall expansion in tomato roots. The effects of inoculation on gene expression between control and exposed plants were compared. The results of this study may have major implications to agriculture by reducing cost and reliance on petroleum based chemicals, as well as to the field of plant physiology. Understanding how plants respond to inoculation with <i>E.</i> 638 may lead to a better understanding of plant responses to external stimuli. </p><p>

Dissertation submitted in compliance with the requirements of the Master's Degree in Technology in Biotechnology, Technikon Natal, 1999. / Sugarcane mosaic potyvirus (SCMV) IS the causal agent of the most important viral disease of sugarcane in South Africa, mosaic. Accurate knowledge of the prevalent SCMV strain(s) in the South African sugar industry is lacking and has never been determined using molecular analysis. Identification of SCMVstrains at the genomic level would provide valuable information for the development of appropriate in vitro diagnostic tests and in the genetic engineering of sugarcane for coat protein (CP) mediated resistance. / M

Brilliant cresyl blue has been used but little in botanical histology. The preparation and methods of use of the stain in squash technique are described. The technique is then used to follow the mitotic cycle in Allium cepa. It is shown to be an excellent morphological stain and it has moreover some promise of being useful in cytology. Some seventy photomicrographs demonstrate its possibilities. / Science, Faculty of / Botany, Department of / Zoology, Department of / Graduate

Interference among neighbouring plants, often due to competition for limited resources, is central to subjects such as yield-density relationships, intercropping, self-thinning in dense plant stands and low reproductive yield in certain crops. An experiment was conducted to investigate plant interference in associated populations of beans {Phaseolus vulgaris L.) and beets [Beta vulgaris L.). Plants of the two species were grown at different total densities and at different mixture proportions in a randomized complete block design. Several analytical procedures were used to interpret and define treatment effects. The analysis of variance indicated that yield was significantly reduced with either increasing total population density or increasing bean proportions in mixtures. The interactions of total population density and mixture proportions were only occasionally significant. Parameters of non-linear models used to define yield-density relationships indicated that beans were the superior competitor, both against themselves and against beets. The model parameters were also used to determine differential yield responses on total dry weight, leaf dry weight, leaf number and leaf area in the bean-beet mixtures. Yield advantage was observed in leaf dry weight and leaf number when model parameters were used in calculating land equivalent ratios whereas total dry weight and leaf area showed yield disadvantage. Using observed values to calculate land equivalent ratios indicated yield advantage in all four variables. Plant size inequalities, as determined by the Gini coefficient tended to decrease in beet monocultures with increasing population density. In monocultures of beans and in the bean-beet mixtures, plant size distribution was not systematically changed by density and mixture treatments. Yield component analysis indicated that the variation in total yield due, to either population density or mixture treatments increased with age; the variation due to the population density by mixture proportions Interaction remained relatively constant throughout the growing season. Leaf number per plant was the yield component which was most frequently a significant source of yield variation both in the forward and backward yield component analysis. Plant growth analysis indicated that leaf area ratio and specific leaf weight were higher at higher population densities and at higher bean proportions. Harvest index decreased with increasing population density and with increasing proportions of the competing species in beets. Absolute growth, relative growth and unit leaf rates increased with time and declined after reaching a peak at about 68 days after planting. Both the lowest population density of 16 plants m ̄² and the mixture treatment with the least proportion of beans had the greatest increase in absolute growth, relative growth and unit leaf rates. Allometric relationships between total plant dry weight and any secondary measure per plant were influenced in different ways by density and mixture treatments and by time of harvest. The composition of models also varied considerably. The interpretation of plant interference, therefore is strongly influenced by the choice of plant characteristics which are measured, and by the time of measurement. / Land and Food Systems, Faculty of / Graduate

Interference among plants involves responses of plants to their environment as modified by the presence and/or growth of neighbouring plants. An important theme of research on plant interference is the relationship between plant population density and measures of plant growth or agricultural yield. An experiment on plant interference was performed in which plots of two important forage species, orchardgrass (Dactylis glomerata L.) and timothy (Phleum pratense L.), were grown at different total population densities and mixture proportions. Measures of plant growth and yield were taken at five separate harvests during one growing season. The analysis of variance indicated that primary and derived measures of growth and yield generally were strongly affected by the three main experimental factors: time, total population density and mixture proportions. Best subset multiple regression analysis, using Mallow's CP criterion, helped to define which experimental factors and interactions were related closely to plant responses. Both of these analytical methods indicated that the main effects of experimental factors were often significant, while interactions among factors were less prominent. The best subset models were different in structure for different response variates, however, indicating that plant responses varied when different measures of growth were considered. Models were developed which provided an effective description of yield-density responses in monocultures and mixtures when interference was strong. Model parameters were used to compare the relative strengths of intraspecific and interspecific interference in each species. The higher-yielding species, timothy, exerted stronger interference, both within and between species than orchardgrass. Interference was significant early in growth and intensified with increasing population density. The parameters of the yield-density models were also used to assess differential yield responses in the mixtures. Net overyielding occurred in most mixtures because overyielding in timothy was not fully offset by underyielding in orchardgrass. The greatest yield advantage occurred in mixtures containing orchardgrass and timothy in proportions of 2:1. The dynamics of plant growth were followed using methods of plant growth analysis. Absolute growth rate, relative growth rate, unit leaf rate and crop growth rate were among the growth indices showing strong responses to interference. Interference seemed to disturb the time course of growth in a complex way. Allometric relationships between dry weight per plant and either leaf area per plant or tiller number per plant were also affected by interference. The species differed in their allometric responses, and the relationships between allometry and different treatment factors also varied. / Land and Food Systems, Faculty of / Graduate

The objective of this study was to compile and interpret nutritional and developmental data for cranberry (Vaccinium macrocarpon Ait.) as the basis for standardizing experimental techniques (particularly data collection) and tissue analysis, including tissue to sample, time of sampling, and normal element concentrations for 'Early Black'. Seasonal nutrient levels were determined in tissues of 'Early Black' cranberry under 10N-8.7P-8.3K fertilization (O, 170, 335, and 505 kg/ha). After three years, N, P, and K concentrations in new shoot tissues were positively affected by N-P-K supply. The N-P-K supply had no effect on Ca and Mg concentrations in new shoot tissue but B concentrations were lowest in unfertilized plants. N, P, K, and Cu concentrations in new shoots declined during the season, whereas those of Ca, Mg, B, and Mn rose. Element concentrations in the tissues indicated that mobilization of elements into new shoots from old leaf and woody stem tissues occurred. In an average crop (17 Mg/ha), 8.5 kg N/ha and 14.7 kg K/ha were removed from the cranberry bog. Vegetative growth (dry weight, upright length) was positively correlated with N-P-K supply, but the highest yields were associated with 335 kg N-P-K/ha. Upright density, percent of uprights flowering, and fruit set were the important determinants of yield. These variables were proposed as standards for data collection. Growing degree day (GDD) accumulations were recorded during this study using a base temperature of 6.5C (lower than previously recommended). Based on GDD accumulations at the canopy level, the correct base temperature for cranberries is most likely 4.5C or lower. However, for a single location over several years, day number was superior to GDD as a predictor of developmental and nutritional status. A period of stable element concentration in new shoot tissue (10 August to 15 September) was identified and recommended as the time to collect cranberry tissue samples for analysis. Mixed vegetative and flowering new upright tips were recommended as the tissue to sample, and standards for 'Early Black' were proposed. Element concentrations in 'Howes', 'Stevens', 'Pilgrim', 'Bergman', and 'Franklin' were determined and compared to the 'Early Black' standard values.

Nuclear-encoded chloroplast proteins are synthesized as precursors in the cytosol with N-terminal cleavable transit peptides. The post translational import of proteins into chloroplasts occurs first through the outer membrane via the Toc complex (Translocon of Outer membrane of Chloroplast). The high fidelity of the protein import process is maintained by the specific recognition of the transit peptide of nucleus-encoded proteins by the coordinate activities of two homologous GTPase Toc receptors, Toc34 and Toc159. Structural and biochemical studies suggest that dimerization of the Toc receptors functions as a component of the mechanism to control access of preproteins to the membrane translocation channel of the translocon chloroplast envelope. I show that specific mutations that disrupt receptor dimerization in vitro reduce the rate of protein import in transgenic Arabidopsis compared to the wild type receptor. The mutations do not affect the GTPase activities of the receptors. Interestingly, these mutations do not disrupt initial preprotein binding at the receptors, but they reduce the efficiency of the transition from preprotein binding to membrane translocation. These data indicate that dimerization of receptors has a direct role in protein import, and support a hypothesis in which conformational changes that initiate membrane translocation of chloroplast preproteins is part of the molecular mechanism of GTP-regulated protein import.

Abstract not available

Increases in photosynthetic rates (A), biomass production and grain yield have been measured across a range of C₃ plants under elevated atmospheric [CO₂] ('eCO₂'). However, decreases in the nutritional status of many C₃ plants growing at eCO₂ often occur concurrently with these increases. Several mechanisms have been proposed for these eCO₂-induced decreases, such as dilution effects due to enhanced carbohydrate production, down-regulation of photosynthesis, reduced root development, and decreased transpiration-driven mass flow delivery of nutrients. Reduced mass flow at eCO₂ is generally accepted as one cause for altered nutrient status in C₃ plants. However, eCO₂-induced reductions in mass flow remain understudied in C₄ plants, even though they account for about 18% of the total global net primary productivity and represent a large food source globally (e.g. maize and sorghum). This thesis investigated how mass flow reductions affect the nutrient status of wheat (C₃) and maize (C₄) plants. Reduced mass flow in both maize and wheat plants was induced with eCO₂ and by varying leaf-to-air vapour pressure deficits (VPD). I hypothesised that reduced mass flow at eCO₂ and at low VPD will negatively affect nutrient status in both the C₃ (wheat) and the C₄ (maize) species. In the first experiment, maize and wheat plants were grown at 400 and 800 ppm [CO₂], in three well-watered soils, ranging from sandy to clayey, with and without fertilisation. In the second experiment, plants were grown at three VPD levels, namely 1.613 kPa, 0.773 kPa and 0.350 kPa, in well-watered soil and sand. In the latter experiment, to demonstrate the importance of mass flow, plants grown in sand were supplied nutrients in such a way that they had to rely exclusively on mass flow or diffusive processes (i.e. limited interception) for nutrient delivery to their rhizosphere. eCO₂ stimulated A on average by 22% in maize and by 50% in wheat, while stomatal conductance (ɡₛ) and cumulative water loss (CWL) were respectively decreased by 35% and 31% in maize, and by 26% and 37% in wheat. eCO₂ reduced mass flow delivery of most nutrients on average by 32% in maize, and by 38% in wheat. The hypothesis that eCO₂-induced reductions in mass flow negatively affect nutrient status in maize 33 and wheat was however not supported. This was attributed to the well-watered conditions of the soils, which may have allowed for other processes (e.g. diffusion) to make up for the mass flow reductions. From 0.773 kPa to 0.350 kPa VPD, CWL was decreased on average by 14% and 20% in the maize and wheat plants, respectively. A and ɡₛ were little affected by VPD, but plants of both species always accumulated more biomass at 0.773 kPa. Consequently, there was little evidence to suggest that VPD-induced reductions in mass flow negatively affect nutrient status in maize and wheat. Reduced CWL may have impeded root-to-shoot transport of ions and reduced dry biomass accumulation in the maize and wheat plants at 0.350 kPa (-40% and -22% on average respectively, relative to 0.773 kPa plants). Tissue [NPK] was also decreased (-13%, -41% and -47% respectively) in the 0.350 kPa VPD sand wheat plants, while increases in the proportion of finer roots may have alleviated effects of reduced CWL on tissue [NPK] in the C₄ species. The findings from both experiments imply a decrease in the importance of mass flow for the delivery of nutrients to the rhizosphere under well-watered conditions. However, reductions in mass flow to a similar extent in both species at eCO₂ and low VPD - measured in the present study - suggest that under conditions of low water and nutrient availability, tissue nutrient concentrations could be negatively affected when transpiration is reduced.

No description available.