Thesis (Ph. D.)--Texas State University--San Marcos, 2009. / Vita. Includes bibliographic references (leaves 19-24, 46-50, 69-74, 97-101,127-131, 141-144). Also available on microfilm.

Thesis ( Ph.D.)--University of Delaware, 2005 . / Principal faculty advisor: D. Janine Sherrier, Dept. of Plant and Soil Sciences. Includes bibliographical references.

In recent years, the rhizobial taxonomy changed significantly with the discovery of novel symbiotic associations between legumes and nodulating bacteria. This was aided by the focus shift from studying only agricultural crops to legumes indigenous to certain regions, ultimately to discover new inoculant strains and to uncover the secrets of the rhizobium¬legume symbiosis. In previous studies on the diversity of South African rhizobia, it has become clear that our country has a wealth of rhizobia. Cyclopia is a legume genus, which belongs to the fynbos biome of South Africa. Honeybush tea is a herbal infusion manufactured from the leaves and stems of certain Cyclopia spp. Commercial cultivation of this potentially new agricultural crop is now developed to protect the natural Cyclopia spp. populations from harvesting and ultimately extinction. Superior inoculant strains are necessary for these commercial seedlings. The diversity of root-nodulating strains isolated from 14 Cyclopia spp. was determined using 16S-23S IGS-RFLP and partial 16S rDNA base sequencing. Based on 16S-23S IGS-RFLP and partial 16S rDNA base sequencing most of the isolates, with the exception of seven strains, were found to belong to the genus Burkholderia. More extensive phylogenetic, symbiotic and phenotypic studies of selected strains were performed using near full-length 168 rDNA base sequencing, nodA base sequencing and substrate utilisation analysis. In the genus Burkholderia, the isolates belonged to the novel root-nodulating species Burkholderia tuberum and several novel, undescribed Burkholderia genotypes. However, no new Burkholderia species could formally be proposed, since DNA-DNA hybridisation analysis, which is a prerequisite for the description of new species could not be performed in our laboratory. The seven strains not affiliated with the Burkholderia genus belonged to two Bradyrhizobium genospecies, R tropici and a possibly new genus in the a-Proteobacteria. The nodA sequences of all the Cyclopia isolates corresponded to a large extent, indicating that different chromosomal genotypes harbour the same symbiotic genotype. All the isolates of the Cyclopia genus appear to be acid-tolerant, which is in agreement with the acidic nature of the soil from which the strains were isolated. / Thesis (PhD(Microbiology))--University of Pretoria, 2004. / Microbiology and Plant Pathology / unrestricted

No description available.

Thesis (MSc)--Stellenbosch University, 2004. / ENGLISH ABSTRACT: This study investigated the activities of several of the enzymes involved in the alternative route of PEP metabolism via PEPc (EC 4.1.1.31). This reaction circumvents the adenyl ate-controlled PK (EC 2.7.1.40) reaction of the conventional glycolytic network under conditions of P stress. It was hypothesized that the synthesis of pyruvate under Pi stress would induce the PEPc alternative route and that C for pyruvate synthesis would primarily be imported via this route. This was assessed by looking at how total enzyme activities are perturbed under P stress and also by following the route of radioactive labelled 14C02 under sufficient (2 mM) and deficient P (2 JlM) conditions in either roots or nodules. The significance of the pathway under P stress, was further assessed by determining pool sizes of pyruvate that was synthesized from PEPc-derived C. The experiments were conducted under glasshouse conditions, as two separate studies: one to investigate the phenomenon of Pi stress and its consequences for PEPc-derived C metabolism, and the other one to study the enzymes involved. Seeds of Lupinus angustifolius (cv. Wonga) were inoculated with Rhizobium sp. (Lupinus) bacteria and grown in hydroponic culture. Tanks were supplied with either 2 JlM P04 (LP) or 2 mM P04 (control) and air containing 360 ppm CO2. Roots experienced pronounced P stress with a greater decline in Pi, compared to nodules. LP roots synthesized more pyruvate from malate than LP nodules, indicating the engagement of the PEPc route under Pi stress. In this regard, pyruvate is considered as a key metabolite under Pi stress. The role of pyruvate accumulation under Pi stress, was further highlighted by the metabolism of PEP via both the PK and PEPc routes. The enhanced PK activities supported these high pyruvate levels. Under P stress, PEPc activities increased in roots but not in nodules and these changes were not related to the expression of the enzyme. Root and nodular PEPc were not regulated by expression, but possibly by posttranslational control. The novelty of our results for symbiotic roots demonstrates that using metabolically available Pi is indeed a more sensitive indicator ofP stress. These results show that under Pi stress, nodules are able to maintain their Pi and adenylate levels, possibly at the expense of the root. It is suggested that nodules do not experience P stress to the same extent as roots or alternatively function optimally under conditions of low P availability. The increase in concentration of pyruvate synthesized from malate, indeed suggest that under LP conditions there is an increase requirement for pyruvate. It is clear from this data that the operation of bypass route in nodules should be investigated further. Nevertheless, this study provided incentives for understanding the role of C pathways in Ni-fixation, in particular under conditions ofP limitation. / AFRIKAANSE OPSOMMING: Die doel van hierdie studie was om die aktiwiteite van verskeie ensieme van die alternatiewe metaboliese roete via phosphoenolpirovaat karboksilase (pEPc, EC 4.1.1.31) te ondersoek. Dié reaksie omseil die adenilaat-beheerde pirovaatkinase (PK, EC 2.7.1.40) reaksie van die konvensionele glikolitiese weg onder toestande van fosfaat (P) stremming. Dit is gepostuleer dat die sintese van pirovaat onder toestande van Pstremming die alternatiewe roete via PEPc sou induseer en dat die koolstof (C) vir pirovaatsintese gevolglik hoofsaaklik vanaf hierdie roete sou kom. Dit is bepaal deur die veranderinge in die totale ensiemaktiwiteite wat sou plaasvind onder P-stremming te ondersoek. Daar is ook gekyk na die roete' wat radioaktiewe C C4C02) sou volg in wortles en wortelknoppies wat behandel is deur blootsteling aan eerder lae fosfaat (2 1lM) of genoegsame fosfaat (2 mM; kontrole), Die betekenis van die alternatiewe roete is ook ondersoek deur die poel-groottes van pirovaat, soos gesintetiseer via die PEPc reaksie, te bepaal. Twee eksperimente is in 'n glashuis uitgevoer. Eerstens is die verskynsel van Pstremming, asook die invloed daarvan op PEPc-afgeleide C-metabolisme, bepaal. Tweedens is die betrokke ensieme bestudeer. Sade van Lupinus angustifolius (cv. Wonga) is geïnokuleer met Rhizobium sp. (Lupinus) bakterieë en in 'n waterkultuur gekweek. Die houers is voorsien met óf2 IlM P04 (LP) óf 2 mM P04 (HP) en lug wat 360 ppm C02 bevat het. Wortels, anders as wortelknoppies, het 'n betekenisvolle afname in anorganiese P (Pi) ervaar. Onder P-stremming, het lae fosfaat wortels meer pirovaat vanaf malaat gesintetiseer as wortelknoppies, wat 'n definitiewe bydrae vanaf die PEPc roete impliseer. Hiervolgens is pirovaat 'n sleutel metaboliet onder P-stremming. Die belangrikheid van die akkumulering van pirovaat onder P-stremmende toestande is verder beklemtoon deur die toename in metabolisme van PEP via beide die PK- en die PEPcreaksies. Die toename in PK-aktiwiteite is goed gekorreleer met die verhoogde produksie van pirovaat. Onder toestande van P-stremming het die aktiwiteit van PEPc in wortels verhoog, maar nie in wortelknoppies nie. Dit was nie die gevolg van 'n verhoogde uitdrukking van die ensiem nie. Wortel- en wortelknoppie- uitdrukking van PEPc is derhalwe nie gereguleer deur die uitdrukking daarvan nie, maar eerder deur post-tranlasie kontrole. Hierdie resultate vir wortels met wortelknoppies demonstreer dat metaboliese Pi 'n beter maatstaf is om P-stres aan te dui. Hierdie resultate toon dat wortelknoppies beter daartoe instaat is om hul Pi-vlakke en adenilaatvlakke te reguleer, en dit mag ten koste van die gasheerwortel wees. Ons stel voor dat wortelknoppies nie P-stremming tot dieselfde mate ervaar as die gasheerwortel nie en dat dié knoppies optimaal funksioneer by lae Pi vlakke. Die verhoogde konsentrasie van pirovaat, wat vanaf malaat gesintetiseer is, impliseer dat daar 'n groter vereiste is vir dié metaboliet onder toestande van Pstremming. Hierdie studie het die rol van koolstofmetabolismein stikstofbindende organismes, spesifiek onder toestande van fosfaat-tekort, beklemtoon.

No description available.

In the soybean nitrogen fixing symbiosis, suboptimal root zone temperatures (RZTs) inhibit the inception and development of nodules, leading to reduced nitrogen fixation and soybean yield. The purpose of this thesis was to evaluate the effects of selected with potential low temperature tolerant strains, originating from the northern areas of the USA, and mutants made from Bradyrhizobium japonicum USDA 110, on soybean nodulation, nitrogen fixation and yield in a short season area with cool spring conditions. Among the 40 B. japonicum strains evaluated, only USDA 30, USDA 31, 532 C and USDA 110 grew well at 15°C. USDA 30 and USDA 31 grew better than 532 C and USDA 110 at 15°C. Mutants Bj 30050--Bj 30059 could not produce lipo-chito-oligosaccharide (LCO) at measurable levels in the absence of genistein. All mutants produced more LCOs than 532 C and USDA 110 at the same temperature and genistein concentration. Temperature and genistein concentration did not affect LCO production dynamics for the following: mutant Bj 30055, 532 C and USDA 110. Both mutant production and identification of low temperature tolerant strains achieved the general objective of improved soybean nitrogen fixation in a cool climate. Inoculation with low temperature tolerant strains (USDA 30, USDA31), or mutants (Bj 30055 and Bj 30058) improved soybean development (increases in leaf area and shoot nitrogen content), nodulation (increases in nodule number and nodule weight), nitrogen fixation and yield relative to inoculation with B. japonicum strain 532 C, the strain currently included in most Canadian soybean inocula.

With the projected increase in global population, unprecedented increases in crop production will be needed and legume crops are one of the primary means of achieving these increases. The legume-Rhizobium symbiosis is the single most important source of biologically fixed nitrogen in agricultural systems but, as a biological system it is complex, and very sensitive to environmental effects, such as available soil nitrogen, soil pH (both high and low), soil salinity and extremes of soil temperature. Each of these may affect the delicate signal exchange process that occurs during symbiosis establishment. To better understand the effect of environmental factors on signal exchange and nodulation, we conducted four experiments, under controlled-environment conditions, with pea (Pisum sativum) as the model legume. The first experiment studied the effects of available nitrogen, the second the effects of low soil pH, the third the effect of soil salinity and the fourth the effects of low soil temperature. In all experiments the plants were inoculated with Rhizobium leguminosarum bv. viceae cells previously treated with 10 x 10-3 M of hesperitin or naringenin, or not treated (control). In all experiments plants were destructively sampled at 10, 20, 30 and 40 days after inoculation (in two experiments samplings were also conducted at 15 DAI), and data on plant and nodule variables were collected. To allow for a better understanding of the effects of flavonoids on nodule development an image analysis technique was developed that permitted us to measure every individual nodule at each sampling. This provided a more precise picture of nodule development over time than would have been possible with previous methods. Our results indicated that addition of flavonoids had positive effects on nodulation, both in number and size of nodules produced, and that the positive effects were greatest at the most inhibitory levels of the environmental factors tested, and at earlier sampling

Jasmonic acid (JA) and its methyl ester, methyl jasmonate (MeJA), collectively termed as jasmonates, are naturally occurring in plants and are important signal molecules involved in induced disease resistance and stress responses of plants. Besides their role in-planta, they are also rhizosecreted by root cells. Germinating soybean seeds exude large quantities of jasmonic acid; however there is no knowledge regarding how jasmonates influence cells of the soybean symbiont, Bradyrhizobium japonicum, in the rhizosphere. We studied the role of jasmonates in the soybean-Bradyrhizobium symbiosis. Bradyrhizobium japonicum cultures were induced with jasmonates and the resulting Nod factors were isolated and purified. Our results showed that JA and MeJA strongly induced the production of Nod factors by the tested B. japonicum strains. When added together, genistein and jasmonates resulted in greater LCO production than either one alone. Jasmonic acid is produced from linoleic and linolenic acids via the octadecanoid pathway; we studied the effect of these two fatty acids on B. japonicum nod gene induction. Interestingly both linoleic and linolenic acids induced the nod genes and caused LCO production by B. japonicum cultures. Since jasmonates induced the nod genes and also caused LCO production in B. japonicum, I conducted experiments in the greenhouse and field to determine whether incubation of B. japonicum with JA or MeJA prior to inoculation increases soybean nodulation variables and grain yield. Both genistein and McJA increased nodule number and nodule dry weight per plant. Due to enhanced nitrogen fixation, attributed to increased nodule number and weight, soybean dry matter accumulation and grain yield were increased. These results document the discovery of jasmonates and their precursors as new signal molecules in the Bradyrhizobium - soybean nitrogen fixing symbiosis.

Thesis (M.S.)--State University of New York at Binghamton, Biological Sciences Department, 2007. / Includes bibliographical references.