Research on efficient management systems to optimise Trifolium repens-Rhizobium symbiosis, is lacking in South Africa. The amount of nitrogen (N) fixed by symbiotic rhizobia in root nodules of T. repens is ultimately determined by health of the soil environment. Soil organic matter (SOM) is the main attribute that will sustain soil health as it affects the chemical, physical and biological aspects of soil. The aim of this study was to determine the potential of T. repens and T. ambiguum to sustain low N input pastures. The hypotheses of this study is that SOM can play an important role in ensuring good soil health, which supports the optimum growth and production of Trifolium spp. in low N input pastures. Four Trifolium repens cultivars were evaluated in field conditions to determine the effect of Rhizobium bacteria on the potential of the cultivars to nodulate. The cultivars Grasslands Huia, Haifa, Ladino and Regal were selected for assessment. The thousand-seed-mass (TSM) of each cultivar was measured to determine the quality and viability of the seed; and to determine the interaction between seed mass and nodulation. Mean TSM values of T. repens cultivars differed significantly, with Huia having the highest TSM followed by Haifa, Ladino and Regal. Biomass production was also measured as an indicator of efficiency of nitrogen fixation. The cultivar Huia, with the heaviest seed, showed the highest biomass production. After eight weeks of growth, the nodulation index was determined from the size, number and colour of the bacterially associated root nodules. All plants, regardless of cultivar, formed nodules within eight weeks. It was concluded that TSM had no notable effect on nodulation. Planting date with associated temperature effects and the intrinsic cultivar effect also had no influence on nodulation. It was therefore concluded that nodulation potential of the four cultivars tested was similar in the specific environmental conditions. The total number of symbiotic rhizobial cells per gram of soil as affected by soil C content and the host plant was also determined. Inoculated and un-inoculated seeds were planted on five soil treatments, each with a different level of soil C. The plant infection technique (most-probable-number/MPN technique) was used to quantify the rhizobial numbers in soil as affected by soil C content and the host plant. The mean MPN-value ranged from 8907 to 78 Rhizobium cells per gram of soil for T. repens treatments, and 0 to 436 for T. ambiguum treatment. Soil C had no effect on the number of Rhizobium bacteria present in the soil. Inoculation however, had a significant effect on the MPN value of T. ambiguum, but not for T. repens. Most symbiotic Rhizobium was detected between a soil C content of 2.03% to 3.80% in both inoculated and non-inoculated soils. The spread plate count was used to determine the total number of symbiotic and saprophytic rhizobia. This method was used to quantify both symbiotic and free-living rhizobia. The effect of different levels of soil C on the amount of atmospheric N fixed was assessed by the N difference technique. Arctotheca calendula (cape weed) served as the reference plant in this study, to determine what percentage of N is derived from the atmosphere (%Ndfa). Biomass production was determined and served as the parameter to establish the efficiency of the Rhizobium bacteria in the soil. Inoculating seed with host specific rhizobia had no effect on the amount of N fixed. The mean %Ndfa differed significantly between soil organic C treatments with the species T. repens but did not differ significantly between soil organic C treatments with T. ambiguum. It was concluded from this study that symbiotic rhizobia introduced by inoculant was much more efficient in higher C content soils than free-living rhizobia, which highlights the importance of inoculation in improving the sustainable production of T. repens pastures. Although the amount of N fixed increased as the level of soil organic matter decreased, the efficiency of N fixation decreased proportionally. This explains the bigger change in soil N content on soil with a high C content. This study has thus highlighted the importance of soil organic carbon in the host specific Rhizobium inoculation sucsess, of T. repens low N input pasture systems. / Dissertation (MSc(Agric))--University of Pretoria, 2010. / Plant Production and Soil Science / unrestricted

Empresa Brasileira de Pesquisa Agropecuária / The objective of this work was evaluate two pasture-based systems (PS) with elephantgrass (Pennisetum purpureum Schum.), ryegrass (Lolium multiflorum Lam.), and spontaneous growth species varying in one system, the mixture with white clover (Trifolium repens L.) and, in the other system, with forage peanut (Arachis pintoi Kraprov & Gregory), handled under rotational grazing. The experiment was done from April 24th, 2007 to April 30th, 2008, totalizing 371 days. In order to evaluate were used four paddocks with 0.25 ha each one, where the elephantgrass was established in lines with a distance of 4 m between lines. In the winter period, in space between lines, was established the ryegrass and in two paddocks the white clover was sown and, in the other two, the forage peanut was preserved, which had already been established. The experimental design was completely randomized, with two treatments (pasture-based systems), two replicates (paddocks) and in subdivided parcels in the time (grazing cycles). The grazing were fertilized with 100, 60 and 100kg/ha de N, P2O5 and K2O, respectively. As experimental animals were used Holstein cows, in lactation, receiving 6 and 5 kg of complementary concentrate feed in winter and summer periods, respectively. The cows live weight was 514±35.9 kg and mean milk production of 20.80±2.23 kg/day. During the evaluation 11 grazing were done, six in the winter period, defined by ryegrass, and 5 in the summer period where the pre and post grazing were analyzed; the botanical compositions of grazing and structural of elephantgrass, ryegrass and legumes; accumulation rates and of disappearance of forage mass; stocking rate and pasture chemical composition (by samples of grazing simulation). The results show that the appraised botanical composition, in each treatment, contributed to compensate the offer and the forage chemical composition during the year. It was verified a better performance in the pasturebased system, using the forage peanut, considering the mean of the accumulation taxe and of disappearance of forage mass. Pasture-based systems showed similar chemical composition, indicating, the need of improving pasture-based systems to raise the pasture mass production at the start winter period, mainly the legumes contribution. / O trabalho foi conduzido com o objetivo de avaliar dois sistemas forrageiros tendo como componentes comuns o capim-elefante (Pennisetum purpureum Schum.), o azevém (Lolium multiflorum Lam.), e as espécies de crescimento espontâneo variando em um sistema o consórcio com o trevo branco (Trifolium repens L.), e em outro, com o amendoim forrageiro (Arachis pintoi Kraprov. & Gregory), manejados sob pastejo rotacionado. O experimento foi realizado no período de 24 de abril de 2007 a 30 de abril de 2008, totalizando 371 dias. Para a avaliação foram usados quatro piquetes com 0,25 ha cada um, onde o capimelefante encontrava-se estabelecido com espaçamento de 4 m entre linhas. No período hibernal, nas entrelinhas do capim-elefante, fez-se o estabelecimento do azevém e em dois piquetes semeou-se o trevo branco e nos outros dois se preservou o amendoim forrageiro, que já se encontrava estabelecido. O delineamento experimental foi o inteiramente casualizado com dois tratamentos (sistemas forrageiros), duas repetições de área (piquetes) e em parcelas subdivididas no tempo (ciclos de pastejo). As pastagens foram adubadas com 100, 60 e 100 kg/ha de N, P2O5 e K2O, respectivamente. Como animais experimentais foram utilizadas vacas em lactação da raça Holandesa, recebendo complementação alimentar de 6 e 5 kg de concentrado/dia nos períodos estival e hibernal, respectivamente. O peso médio das vacas foi de 514±35,9 kg e produção média de leite de 20,80±2,23 kg/dia. Durante a avaliação foram realizados 11 pastejos, seis no período hibernal, definido pela participação do azevém, e cinco no período estival, avaliando-se a massa de forragem de pré e pós-pastejo; as composições botânica da pastagem e estrutural do capim-elefante, do azevém e das leguminosas; as taxas de acúmulo e de desaparecimento de matéria seca; a carga animal e a composição química do pasto (a partir de amostras de simulação de pastejo). Os resultados demonstram que a composição botânica avaliada em cada tratamento contribuiu para equilibrar, em parte, a oferta e a composição química da forragem no decorrer do ano. Considerando-se os dados médios da massa de forragem, das taxas de acúmulo e de desaparecimento de matéria seca, e a lotação, verificou-se melhor desempenho no sistema forrageiro envolvendo o amendoim forrageiro. Os sistemas forrageiros apresentaram composição química similar, apontando para um sinergismo entre as espécies de gramíneas e leguminosas. No entanto, observa-se a necessidade de se aperfeiçoar os sistemas forrageiros para elevar a produção de massa de forragem no início do período hibernal, especialmente em relação à contribuição das leguminosas.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The objective of this study was to conduct analysis of data from six experiments with forage systems with Elephant Grass (EG) + Italian Ryegrass (IR) + Spontaneous Growing Species (SGS); EG + IR + SGS + Forage Peanut; and EG + IR + SGS + White or Red Clover, conducted in the Laboratório de Bovinocultura de Leite da Universidade Federal de Santa Maria, with rotational grazing using dairy cattle. The experiments analyzed were conducted between the years 2005 to 2013 and grouped by the month they grazing cycles were performed. Holstein dairy cows were used for evaluation, with an average body weight and milk production of 543 kg and 19 kg/day, respectively. The total forage production values and the average stocking rate and crude protein levels were 13.8, 16.5 and 16.8 t/ha; 2.90; 2.91 and 2.92 AU/ha/day and 17.5, 18.6 and 18.2%, for the respective forage systems. The forage systems consisting by forage legumes presented the best results in relation to pasture productivity and nutritive value of forage. The mixed with forage peanut controlled the spontaneous growing species and participated in the herbage mass throughout the year. In mixed pasture with clovers the nitrogen contribution to the system resulted in better conditions for the development of grasses forage (Italian ryegrass or elephant grass). / O objetivo desse estudo foi comparar sistemas forrageiros sem leguminosa e em consórcio, por meio de uma análise conjunta de dados provenientes de seis experimentos conduzidos no Laboratório de Bovinocultura de Leite da Universidade Federal de Santa Maria. Os sistemas forrageiros constituíram-se por capim elefante (CE) + azevém (AZ) + espécies de crescimento espontâneo (ECE), sem leguminosa; CE + AZ + ECE + amendoim forrageiro; e CE + AZ + ECE + trevo branco ou vermelho. Os experimentos foram realizados entre os anos de 2005 a 2013 e agrupados pelo mês em que foram efetuados os ciclos de pastejo. Para avaliação foram usadas vacas em lactação da raça Holandesa, com peso corporal e produção de leite média de 543 kg e 19 kg/dia, respectivamente. Os valores de produção de forragem e as médias de taxa de lotação e dos teores de proteína bruta foram de 13,8; 16,5 e 16,8 t/ha; 2,90; 2,91 e 2,92 UA/ha/dia e 17,5; 18,6 e 18,2%, para os respectivos sistemas forrageiros. Os sistemas forrageiros constituídos por leguminosas apresentaram os melhores resultados em relação à produtividade do pasto e ao valor nutritivo da forragem. O consórcio com amendoim forrageiro controlou as espécies de crescimento espontâneo e participou da massa de forragem durante todo o ano. No consórcio com trevos a contribuição de nitrogênio ao sistema implicou em melhores condições para o desenvolvimento das gramíneas acompanhantes (azevém ou capim elefante).

Memoria para optar al Título Profesional de: Ingeniero Agrónomo / Se evaluó el potencial fitoacumulador de ballica (Lolium perenne L.) y/o trébol blanco (Trifolium repens L.) para ofrecer una alternativa de limpieza de sitios contaminados con cobre. Se realizó un ensayo con suelos de la V Región (Valparaíso) de Chile cultivados con vid de mesa (Vitis vinifera L.) que mostraban un alto (TB: bajos rendimientos de V. vinifera), bajo (TA: altos rendimientos de V. vinifera) e intermedio (TM: rendimientos medios de V. vinifera) nivel de Cu (DTPA) disponible (140, 40 y 90 mg kg-1, respectivamente). Durante el año 2013 y en invernadero, cada suelo (cinco repeticiones) fue sembrado con L. perenne y/o T. repens en macetas. Después de ocho meses las plantas fueron cosechadas para obtener la masa de materia seca y los contenidos de Cu tanto en los tejidos aéreos como radicales de las plantas. Así también, se determinaron los contenidos de Cu disponible, intercambiable y total de los suelos. Para las condiciones iniciales de CuDTPA intermedio y alto (TM y TB), el metal fue acumulado principalmente a nivel de raíces en los cultivos individuales y la combinación de ellos, pero ballica y ballica+trébol fueron más eficientes en cuanto a la absorción de Cu. Si bien las especies vegetales son capaces de remover el metal de los suelos, los contenidos de Cu al final del ensayo permanecieron altos (hasta 50 mg kg-1 de Cu disponible), denotando la necesidad de realizar estudios de más largo plazo y de verificar que estos resultados se repitan a nivel de campo. / To assess their potential as copper phytoaccumulators in soils and to offer a cleanup alternative of contaminated sites, ryegrass (Lolium perenne L.) and/or white clover (Trifolium repens L.) were used. The study was conducted with soil from the 5th Region (Valparaíso) of Chile cultivated with table grapes (Vitis vinifera L.) and showing a high (TB: low yields of V. vinifera), low (TA: high yields of V. vinifera) and intermediate (TM: medium yields of V. vinifera) levels of available Cu (DTPA). During 2013 and in a greenhouse assay, each soil (five replications) was sowed with L. perenne and/or T. repens in pots. After eight months plants were harvested to obtain dry matter and Cu contents in plant aerial and root tissues. Available, exchangeable and total Cu were measured also in soils. Under initial high and intermediate levels of CuDTPA conditions (TB and TM), metal was accumulated mainly at roots level in single and combined crops, but single ryegrass and ryegrass+clover were more efficient in the Cu uptake. Although species are able to remove metal from soils, the Cu contents at the end remained high (up to 50 mg kg-1 of available Cu), indicating that long-term trials are necessary and confirm these results at field level.

No description available.

Phosphate (P) supply is one of the major determining factors to plant productivity, since the element affects the growth and the development of plants. In response to Pdeficiency treatment, plants display alterations in root system architecture caused by changes in primary root (PR) and lateral root (LR) length and LR density. In this thesis, the root growth of the agronomically important legume, white clover (Trifolium repens L.) was found to be slightly stimulated in terms of PR length, LR number and total LR length when plants were grown in a P-deficient media (0.01 mM orthophosphate; Pi) when compared with plants grown in a P-sufficient media (1.00 mM Pi) when using a hydroponic growth system. When plants are grown in a P-sufficient media, treatment with 100 nM exogenous 1- aminocyclopropane-1-carboxylic acid (ACC) and exogenous auxin (5 nM 1- naphthylacetic acid, NAA) resulted in significant increases in white clover PR length, LR number and LR length. However, when ethylene action or auxin transport were inhibited using 300 ppm 1-methylcyclopropene (1-MCP) and 100 nM 1-Nnaphthylphthalamic acid (NPA), respectively, root growth was significantly reduced which suggests roles for ethylene and auxin in mediating white clover root growth. To examine the effects of these hormones on plants grown in P-deficient media, 100 nM ACC treatment significantly enhanced the stimulatory effects of growth on Pdeficient media only, while exposure of plants to P-deficiency alone was sufficient to significantly neutralise the inhibitory effects of 1-MCP on root growth. Hence, exposure to P-deficiency is proposed to increase either ethylene biosynthesis or ethylene sensitivity in white clover roots. In contrast, for plants grown in P-deficient media, treatment with 5 nM NAA significantly abolished the stimulation of white clover root growth observed with P-deficiency so it is proposed that exposure to Pdeficiency increases either auxin biosynthesis or auxin sensitivity, but the 5nM NAA concentration used was too high to stimulate root growth. Using DR5p::GUS transgenic white clover, auxin activity was found in the root tips and root primordia. Using these plants, it is suggested that P-deficient treatment and ACC treatment influenced white clover root growth through an increase in auxin sensitivity. Overall, ethylene and auxin are found to be essential in mediating white clover root growth in P-sufficiency, and also in mediating root responses to P-deficiency through changes in terms of the biosynthesis and the sensitivity of these two hormones.

Phosphate (P) supply is one of the major determining factors to plant productivity, since the element affects the growth and the development of plants. In response to Pdeficiency treatment, plants display alterations in root system architecture caused by changes in primary root (PR) and lateral root (LR) length and LR density. In this thesis, the root growth of the agronomically important legume, white clover (Trifolium repens L.) was found to be slightly stimulated in terms of PR length, LR number and total LR length when plants were grown in a P-deficient media (0.01 mM orthophosphate; Pi) when compared with plants grown in a P-sufficient media (1.00 mM Pi) when using a hydroponic growth system. When plants are grown in a P-sufficient media, treatment with 100 nM exogenous 1- aminocyclopropane-1-carboxylic acid (ACC) and exogenous auxin (5 nM 1- naphthylacetic acid, NAA) resulted in significant increases in white clover PR length, LR number and LR length. However, when ethylene action or auxin transport were inhibited using 300 ppm 1-methylcyclopropene (1-MCP) and 100 nM 1-Nnaphthylphthalamic acid (NPA), respectively, root growth was significantly reduced which suggests roles for ethylene and auxin in mediating white clover root growth. To examine the effects of these hormones on plants grown in P-deficient media, 100 nM ACC treatment significantly enhanced the stimulatory effects of growth on Pdeficient media only, while exposure of plants to P-deficiency alone was sufficient to significantly neutralise the inhibitory effects of 1-MCP on root growth. Hence, exposure to P-deficiency is proposed to increase either ethylene biosynthesis or ethylene sensitivity in white clover roots. In contrast, for plants grown in P-deficient media, treatment with 5 nM NAA significantly abolished the stimulation of white clover root growth observed with P-deficiency so it is proposed that exposure to Pdeficiency increases either auxin biosynthesis or auxin sensitivity, but the 5nM NAA concentration used was too high to stimulate root growth. Using DR5p::GUS transgenic white clover, auxin activity was found in the root tips and root primordia. Using these plants, it is suggested that P-deficient treatment and ACC treatment influenced white clover root growth through an increase in auxin sensitivity. Overall, ethylene and auxin are found to be essential in mediating white clover root growth in P-sufficiency, and also in mediating root responses to P-deficiency through changes in terms of the biosynthesis and the sensitivity of these two hormones.

The investigation in this thesis is divided into two parts. In the first part, the expression and accumulation of 1-aminocyclopropane-1-carboxylic acid (ACC) oxidase (ACO), the enzyme which catalyses the final step of ethylene biosynthesis in higher plants, is examined during exposure of white clover (Trifolium repens L.) to a water deficit. The second part of this thesis is focused on the identification and characterisation of a water-deficit-associated ACC synthase (ACS), the enzyme which catalyses the production of ACC. In the first part, two white clover varieties with differing sensitivity to water deficit, a drought-tolerant Tienshan ecotype and a drought-sensitive Grasslands Challenge cv. Kopu II cultivar were exposed to two water deficit treatments: one cycle of water deficit (designated non-prestressed; NPS) and a water deficit, a rehydration period and then a second water deficit treatment (designated pre-stressed; PS) in the New Zealand Climate Environment Laboratory (NZCEL). Treatments were terminated when the petiole elongation rate (PER) in the first fully-expanded leaf reached zero. Water relations, growth responses, the expression of the white clover ACO genes, TR-ACO1 TR-ACO2 and TR-ACO3 and the accumulation of two of the corresponding proteins, TR-ACO1 and TR-ACO2, were then examined. The soil water content (SWC) and leaf water potential (LWP) measured in both varieties and in both water deficit treatments declined progressively. The rate of decline in SWC and LWP was slower in the Tienshan ecotype with no difference between the NPS and PS treatments. However, the LWP in the Tienshan ecotype at the point at which the PER ceased was less negative (ca. -1.4 MPa) compared to Kopu (ca. -1.7 MPa). In addition, the decline in the PER differed between NPS- and PS-treated Kopu. In the NPS-treated Kopu, the PER was maintained at a high rate when plants were exposed to SWC above 18%, but declined sharply as the SWC declined further. However, in the PS-treated Kopu, the PER declined more progressively in a similar pattern to that determined for NPS- and PS-treated Tienshan. Expression of TR-ACO1 and accumulation of TR-ACO1 was observed in the apical structure of the stolon. As the water deficit progressed, no significant alteration in TR-ACO1 expression and TR-ACO1 protein accumulation was observed in the apical structures of both the NPS- and PS-treated Tienshan ecotype suggesting some degree of protection of the meristem tissues in this more drought-tolerant variety. However, a discernable decline in expression of TR-ACO1 and accumulation of TR-ACO1 protein was observed in the NPS-treated Kopu suggesting some degree of tissue injury in this more drought-susceptible variety. However, after the pre-stress (PS) treatment, no real changes in TR-ACO1 expression and TR-ACO1 protein accumulation were observed, in common with the observations for the NPS- and PS-treated Tienshan ecotype suggesting that meristem protection may now be occurring. The results suggest further that the pre-stress treatment of the more drought-susceptible Kopu may result in a degree of acclimation to the water deficit. For the first-fully expanded leaves, expression of two transcripts, TR-ACO2 and TR-ACO3 and accumulation of TR-ACO2 protein was monitored as the SWC decreased. The expression of TR-ACO2 and accumulation of TR-ACO2 decreased as the water deficit progressed in both the NPS- and PS-treated Tienshan ecotype and correlated with the decrease in PER. By contrast, in the NPS-treated Kopu, TR-ACO2 expression and TR-ACO2 protein accumulation increased, but again, after a period of pre-stress, TR-ACO2 expression and TR-ACO2 accumulation decreased, in common with the Tienshan ecotype. Again, the pre-stress treatment of the drought-susceptible Kopu may result in a degree of acclimation to the water deficit such that the responses become similar to those observed in the more drought-tolerant Tienshan ecotype. However, in both NPS- and PS-treated Tienshan and Kopu there was no significant alteration in the expression of TR-ACO3 in the first fully-expanded leaf. The expression of TR-ACO2 and TR-ACO3 and accumulation of TR-ACO2 protein were also observed in the second fully-expanded leaves (an older tissue). Again similar patterns in the expression of TR-ACO2 and TR-ACO3 and accumulation of TR-ACO2 protein were observed in both NPS- and PS-treated Tienshan and Kopu. In these leaves, expression of TR-ACO2 and accumulation of TR-ACO2 protein decreased as the water deficit progressed, but expression of TR-ACO3 increased as the water deficit decreased to less than 10%. These results suggest that responses of younger tissues (apical structure; first-fully expanded leaf) maybe the critical determinant for the tolerant (or otherwise) of white clover plants to water deficit. In the second part of this thesis, four ACS genes were identified from the Tienshan ecotype exposed to water deficit and designated TR-ACS-T. Three of these were similar to previously identified TR-ACS genes from Grasslands Challenge genotype 10F while the fourth was a novel gene designated TR-ACS4-T. TR-ACS4-T is 64%, 64% and 63% homologous to TR-ACS1-T, TR-ACS2-T and TR-ACS3-T, respectively in terms of nucleotide sequence. In the GeneBank database, TR-ACS4-T shares highly homology to ACC synthase sequences from a wide range of tissues including seedlings and fruit tissues, in addition to a high homology to ACS genes induced in auxin-, wounding- and ethylene-treated tissues. The pattern of TR-ACS4-T expression observed during leaf development suggests that the gene is expressed initially in the apical structures and in the newly initiated leaves, and then again in the later mature leaves and those at the onset of senescence. Expression decreases again during senescence. TR-ACS4-T expression is not altered by water deficit, but is induced by both ethylene and NAA treatment, but the auxin-induced TR-ACS4-T is mediated by ethylene treatment.

Phosphate (P) supply is one of the major determining factors to plant productivity, since the element affects the growth and the development of plants. In response to Pdeficiency treatment, plants display alterations in root system architecture caused by changes in primary root (PR) and lateral root (LR) length and LR density. In this thesis, the root growth of the agronomically important legume, white clover (Trifolium repens L.) was found to be slightly stimulated in terms of PR length, LR number and total LR length when plants were grown in a P-deficient media (0.01 mM orthophosphate; Pi) when compared with plants grown in a P-sufficient media (1.00 mM Pi) when using a hydroponic growth system. When plants are grown in a P-sufficient media, treatment with 100 nM exogenous 1- aminocyclopropane-1-carboxylic acid (ACC) and exogenous auxin (5 nM 1- naphthylacetic acid, NAA) resulted in significant increases in white clover PR length, LR number and LR length. However, when ethylene action or auxin transport were inhibited using 300 ppm 1-methylcyclopropene (1-MCP) and 100 nM 1-Nnaphthylphthalamic acid (NPA), respectively, root growth was significantly reduced which suggests roles for ethylene and auxin in mediating white clover root growth. To examine the effects of these hormones on plants grown in P-deficient media, 100 nM ACC treatment significantly enhanced the stimulatory effects of growth on Pdeficient media only, while exposure of plants to P-deficiency alone was sufficient to significantly neutralise the inhibitory effects of 1-MCP on root growth. Hence, exposure to P-deficiency is proposed to increase either ethylene biosynthesis or ethylene sensitivity in white clover roots. In contrast, for plants grown in P-deficient media, treatment with 5 nM NAA significantly abolished the stimulation of white clover root growth observed with P-deficiency so it is proposed that exposure to Pdeficiency increases either auxin biosynthesis or auxin sensitivity, but the 5nM NAA concentration used was too high to stimulate root growth. Using DR5p::GUS transgenic white clover, auxin activity was found in the root tips and root primordia. Using these plants, it is suggested that P-deficient treatment and ACC treatment influenced white clover root growth through an increase in auxin sensitivity. Overall, ethylene and auxin are found to be essential in mediating white clover root growth in P-sufficiency, and also in mediating root responses to P-deficiency through changes in terms of the biosynthesis and the sensitivity of these two hormones.

Phosphate (P) supply is one of the major determining factors to plant productivity, since the element affects the growth and the development of plants. In response to Pdeficiency treatment, plants display alterations in root system architecture caused by changes in primary root (PR) and lateral root (LR) length and LR density. In this thesis, the root growth of the agronomically important legume, white clover (Trifolium repens L.) was found to be slightly stimulated in terms of PR length, LR number and total LR length when plants were grown in a P-deficient media (0.01 mM orthophosphate; Pi) when compared with plants grown in a P-sufficient media (1.00 mM Pi) when using a hydroponic growth system. When plants are grown in a P-sufficient media, treatment with 100 nM exogenous 1- aminocyclopropane-1-carboxylic acid (ACC) and exogenous auxin (5 nM 1- naphthylacetic acid, NAA) resulted in significant increases in white clover PR length, LR number and LR length. However, when ethylene action or auxin transport were inhibited using 300 ppm 1-methylcyclopropene (1-MCP) and 100 nM 1-Nnaphthylphthalamic acid (NPA), respectively, root growth was significantly reduced which suggests roles for ethylene and auxin in mediating white clover root growth. To examine the effects of these hormones on plants grown in P-deficient media, 100 nM ACC treatment significantly enhanced the stimulatory effects of growth on Pdeficient media only, while exposure of plants to P-deficiency alone was sufficient to significantly neutralise the inhibitory effects of 1-MCP on root growth. Hence, exposure to P-deficiency is proposed to increase either ethylene biosynthesis or ethylene sensitivity in white clover roots. In contrast, for plants grown in P-deficient media, treatment with 5 nM NAA significantly abolished the stimulation of white clover root growth observed with P-deficiency so it is proposed that exposure to Pdeficiency increases either auxin biosynthesis or auxin sensitivity, but the 5nM NAA concentration used was too high to stimulate root growth. Using DR5p::GUS transgenic white clover, auxin activity was found in the root tips and root primordia. Using these plants, it is suggested that P-deficient treatment and ACC treatment influenced white clover root growth through an increase in auxin sensitivity. Overall, ethylene and auxin are found to be essential in mediating white clover root growth in P-sufficiency, and also in mediating root responses to P-deficiency through changes in terms of the biosynthesis and the sensitivity of these two hormones.