The present study sought to define a possible role of phosphorus-stimulated ammoniagenesis, previously observed in vitro and in experimental animals, in the hypocalciuric effect of phosphorus in young men. It was hypothesized that titrating some of the hydrogen ions destined for excretion with ammonia would be beneficial to kidney calcium reabsorption because ammonium ion unlike hydrogen ion does not increase urinary calcium loss. To test this hypothesis, seven young men (22 - 31 years old and average weight of 70 kg) were fed a single menu providing 800 mg phosphorus, 1200 mg calcium, 11.7 MJ (~ 2800 kcal) and 14.5 g nitrogen for 10 days. In a subsequent 10-day period, dietary phosphorus was doubled to 1600 mg by the addition of cheddar cheese and milk to the menu. Dietary nitrogen, calcium and vitamin D were equalized for the two periods. Three 24-hour urine samples and a fasting blood sample were collected at the end of each experimental period. Comparison of period 2 with 1 showed urinary phosphorus excretion + 82%, urinary calcium excretion - 38%, serum phosphorus + 6.2%, serum calcium - 3.8%, urinary sulfate and creatinine excretion no change. Urinary ammonia nitrogen excretion increased in all seven subjects with an average increase of 13%. Furthermore each individual increase in ammonia nitrogen excretion was found to be directly correlated with urinary phosphorus excretion (r = 0.76, P < 0.05). Urinary urea nitrogen excretion was found to vary inversely with urinary ammonia nitrogen excretion with an average decrease of 12% and urinary total nitrogen excretion decreased 14% for the entire group. Results obtained therefore offer a mechanism by which phosphorus directly improves the non-parathyroid hormone portion of tubular calcium reabsorption. The magnitude of the effects seen however suggest that phosphorus-stimulated ammoniagenesis only plays a small role in the mechanism of the hypocalciuric effect of phosphorus in young men. / Graduation date: 1996

No description available.

Graduation date: 2000

Bibliography: leaves 89-104. In this study an EMS-mutated Arabidopsis mutant pho2, which accumulates Pi in leaves, was used to study Pi uptake and transport by comparing it to wild-type seedlings. The study aimed to define the physiological lesions in pho2 mutant and to obtain evidence regarding the function of the PHO2 gene in P nutrition in higher plants. Accumulation of Pi in leaves of pho2 was found to reside in the symplast and was not related to Zn-deficiency. The physiology of the pho2 mutant is consistent with either a block in Pi transport in phloem from shoots to roots or an inability of shoot cells to regulate internal Pi concentration. Southern block analysis revealed that the two transporter genes, APT1 and APT2 were not responsible for the pho2 mutant. Data from the mapping of the PHO2 gene along with information from the Arabidopsis genome sequencing will form the basis for cloning the PHO2 gene in the future.

Bibliography: leaves 89-104. / vi, 104 leaves, [15] leaves of plates : ill. (chiefly col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / In this study an EMS-mutated Arabidopsis mutant pho2, which accumulates Pi in leaves, was used to study Pi uptake and transport by comparing it to wild-type seedlings. The study aimed to define the physiological lesions in pho2 mutant and to obtain evidence regarding the function of the PHO2 gene in P nutrition in higher plants. Accumulation of Pi in leaves of pho2 was found to reside in the symplast and was not related to Zn-deficiency. The physiology of the pho2 mutant is consistent with either a block in Pi transport in phloem from shoots to roots or an inability of shoot cells to regulate internal Pi concentration. Southern block analysis revealed that the two transporter genes, APT1 and APT2 were not responsible for the pho2 mutant. Data from the mapping of the PHO2 gene along with information from the Arabidopsis genome sequencing will form the basis for cloning the PHO2 gene in the future. / Thesis (Ph.D.)--University of Adelaide, Dept. of Plant Science, 1999

The value of the adenylate energy charge [(ATP)+1/2(ADP)/(ATP)+(ADP)+(AMP)] in Azotobacter vinelandii cells was monitored during growth and germination in flask cultures. The miximal value of 0.88 was attained during mid-log phase; this declined gradually to 0.50 by late stationary phase. When these cultures were transferred to encystment media, the adenylate energy charge decreased to an average value of 0.40 as the vegetative cells encysted and remained unchanged during the next 20 days. Encystment cultures wre composed of vegetative cells, encysting cells and mature cysts but the proportionate value of the energy charge could be assigned. Viability of the total population remained 95% or higher during the entire period studied. Azotobacter vinelandii cysts cultivated on phosphate-sufficient media. Although cell protein and nucleic acids were unaffected by phosphate deficiency, cell wall structures, oxygen uptake and sncystment were significantly affected. Phosphate-limited cysts contained much larger amounts of poly-beta-hydroxybutyric acid but had a lower adenylate energy charge than did control cysts. The ATP/ADP ratio was much lower in phosophate-deficient cysts than in the control cysts. The data indicate a "substrate saving" choice of three metabolic pathways available to cells of Azotobacter under different growth conditions.

Accelerated eutrophication is becoming a major problem in relation to surface waters. Controversy has arisen as to its causes in different types of natural systems. Investigations were made of the stimulatory and limiting effects of phosphate on the bacterium E. coli in synthetic media. Growth was measured in batch and continuous flow cultures using both turbidimetric and respirometric techniques. The results obtained were used to formulate a hypothesis concerning the stimulation of algae by inorganic carbon produced by bacteria and the role this relationship plays in the eutrophic processes that occur in natural systems where organic carbon is not limiting to bacterial populations. / Master of Science

Soybean is emerging as a very important food, market and oil crop in Ethiopia. However, its productivity in Western Ethiopia is constrained by several production constraints, of which soil acidity is one of the most important ones. On acidic soils the availability of several plant nutrients is limited; among which phosphorus is the least available. Thus, development of high yielding and low P tolerant soybean varieties need to be among the top priorities in areas with such problematic soils. Therefore, the objectives of the study were to: 1) conduct a Participatory Rural Appraisal (PRA) study to assess farmers’ perception on various soil fertility, soybean consumption and marketing issues, 2) evaluate soybean genotypes under low and high P regimes, and 3) conduct genetic analysis of soybean performance under low and high P conditions. The PRA was conducted to assess farmers’ perception on various soil fertility, soybean consumptions and market issues. A total of 186 soybean producing farmers across three locations of Western Ethiopia were interviewed using a semi-structured questionnaire. Results from the study indicated that the use of soybean for crop rotation and soil fertility improvement was more important to the farmers than household consumption and marketing of the crop. The study also revealed poor demand for soybean compared to other crops on the local market. The majority of respondent farmers’ recognized that soil fertility has been declining over time and obtaining inorganic fertilizers on time was difficult; mainly due to high price of fertilizer. Though farmers’ cooperative was identified as the major supplier of fertilizer, farmers rated the quality of its service in supplying fertilizer as poor. With deteriorating soil fertility and limited capacity to use inorganic fertilizers, farmers are producing soybean under low soil fertility conditions. Thus, breeding programs need to develop varieties that perform well under low fertility soil. Screening soybean genotypes for response to different P regimes was performed in a field experiment using a split plot design, where the main plots were three levels of applied P (0, 100 and 200 kg ha-1 P), and the sub plots were 36 soybean genotypes (G) planted across three locations (L) with two replications. The extent of genetic variation of the 36 soybean genotypes was assessed under low (0 kg ha-1) and high P (100 kg ha-1) conditions. The analysis of variance revealed significant differences among genotypes for all the traits, except pod number at low P; while all the traits, except root volume, pod number, and number of seeds per pod showed significant differences at high P. Plant fresh weight, root fresh weight and root volume exhibited high genotypic coefficient of variation (GCV) and phenotypic coefficient of variation (PCV) under both P conditions. Both principal component and cluster analyses revealed variation in the population. The 100-seed weight, plant height, roots and plant fresh weight combined high heritability and genetic advance estimates indicating that the inheritance of such traits is controlled by additive gene action under both P conditions. In general, the study revealed high genetic variation in the population, which can be exploited to improve performance under both high and low P conditions. The analysis of variance revealed significant genotype X phosphorus (GXP) interaction for number of nodules and total nodule weight at Jimma, and Assossa, and for root weight and root volume at Mettu. Though the GXP and GXPXL interactions showed non-significant difference for across locations analysis, the genotypes displayed significant difference for root fresh weight, root volume, tap root length, and weight of effective nodule. Genotypes: Pr-142 (26), AGS-3-1, SCS-1, AGS 234, and H 3 were identified among the best for root and nodulation characteristics. Yield and yield related traits were also assessed separately in the screening program. The results revealed significant GXP interactions for grain yield only at one site; while the genotypes exhibited highly significant differences for most of the traits in all the sites. G and GXL interaction were significantly different for most the traits. Essex 1, IAC 11, and AGS-3-1 were the best performing genotypes at high P; while genotypes IAC 11, AA 7138, G 9945 and AGS-7-1 displayed tolerance to low P. Genotypes AA-7138, PR-142 (26) and H3 exhibited stable performance across the three P levels. These genotypes have paramount significance in breeding soybean for low P tolerance and stable performance in varying P conditions for resource poor subsistence farmers.The genetic control mechanism for the major quantitative traits for performance under high and low P condition was studied in a nine parent half diallel cross. The results revealed that the GCA effects were highly significant for grain yield, pod length, days to maturity and plant height under low-P conditions. GCA effects were highly significant for grain yield, 100-seed weight, days to maturity, plant height, pod number, and pod length under high P. GCA effects were also significant for number of seeds per pod under high P condition. In addition, the relative contribution of GCA was higher than SCA under both P conditions, except for 100-seed weight at low P. Variety Hardee-1 was the best general combiner for most of the quantitative traits under both P conditions, indicating that it can be used in breeding programs to improve soybean for better genetic response to low and high P. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2012.

The aim of the study was to determine the effect of day/night temperatures (22/l6°C, 2712l oC and 33/27°C) and phosphorus levels (0, 0.12 and 1.2g per 20 kg soil) on seedling establishment and seed viability during three stages of seed development (15, 22 and 33 days after flowering) for seed of normal and quality protein maize cultivars. Soluble carbohydrate accumulation and mineral element content were determined using environmental scanning electron microscopy (ESEM) in relation to seed phytate levels and seed germination capacity at different stages of development. Leaf emergence rate and plant height during seed development were significantly (P < 0.05) influenced by temperature and phosphorus nutrition. Phosphorus in seed is stored primarily in the form of phytic acid, also known as phytate. Accumulation of phytate takes place during maturation phase of seed development. Phosphorus nutrition and temperature also caused a.significant (P < 0.05) increase in seed germination at all stages of seed development. Furthermore, phosphorus nutrition and temperature influenced occurrence of soluble carbohydrates in seeds. Myo-inositol, the sugar alcohol that forms the basic structure of phytate, was increased by P nutrition and increasing growth temperature. Whereas, QPM maize was generally found to perform poorly than normal maize, with respect to phytate content, seed germination and seedling establishment, both cultivars displayed the same responses to phosphorus nutrition and temperature. In both cultivars, globoids, the sites of phytate synthesis and storage, were found only in the embryonic axis. Subsequently, there were significantly low levels of mineral elements (P, Mg and K) found in the endosperm, compared with embryonic axis. This finding suggested that the embryonic axis plays a major role in seed performance, through its effects emanating from phyate metabolism. Myo-inositol plays a role in membrane biogenesis during stress conditions such as temperature by maintaining the integrity of the cell wall and minimizes the leaching of cations essential during germination. Myo-inositol, although it occurs in small concentrations, could be used to indicate seed quality in maize, because its accumulation was found to be associated with enhanced phyate levels and better seed germination in a wide range of temperatures. Low vigour seeds are associated with high electrolyte leakage during imbibition. Mineral elements form a significant portion of the imbibition leachate, which causes seeds to lose nutrients for early seedling growth. This study provided evidence that phosphorus nutrition can alleviate poor seed vigour of maize by improving phytate levels. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2006.