Typescript (photocopy). / Digitized by Kansas Correctional Industries

Orientador: Renato de Mello Prado / Coorientador: Rogério Falleiros Carvalho / Banca: Arthur Bernardes Cecilio Filho / Banca: Cid Naudi Silva Campos / Banca: Lucas Aparecido Gaion / Banca: Lilian Ellen Pino / Resumo: Uma consequência da toxicidade de amônio (NH4+) é a diminuição do conteúdo de citocininas (CKs). Dessa forma, o fornecimento de CK, na forma de trans-zeatina (tZ), pode aliviar a toxicidade de NH4+, e a CK sintética 6-benziladenina (BA), de menor custo, ainda não foi estudada quanto ao seu efeito sobre a toxicidade de NH4+. Além disso, o silício (Si), que é um elemento benéfico, é capaz de amenizar vários estresses, como a toxicidade de NH4+. Objetivou-se verificar se o alívio da toxicidade de NH4+ com o uso do Si é dependente do aumento do teor de CKs no tomateiro cv Micro-Tom (MT), os efeitos do Si no tomateiro transgênico MT CKX2 (baixo teor de CKs) submetido à toxicidade de NH4+ e se o regulador de crescimento BA alivia a toxicidade de NH4+ no tomateiro MT. Para isso, realizaram-se cinco experimentos em tomateiro, com a aplicação dos tratamentos na solução nutritiva. No experimento com concentrações de NH4+ entre 1,25 e 7,5 mmol L-1, 5,9 mmol L-1 provocou a toxicidade de NH4+, com diminiução de 10% na massa seca da parte aérea. No experimento com concentrações de Si entre 0,2 e 0,8 mmol L-1, na forma de silicato de potássio (SiK) ou ácido silícico estabilizado (ASiE), a toxicidade de NH4+ não foi aliviada. No experimento com concentrações de Si entre 1,0 e 2,5 mmol L-1, na forma de SiK, a concentração de 1,29 mmol L-1 de Si aliviou a toxicidade de NH4+. No experimento com N nas formas de NO3- ou NH4+ (5,9 mmol L-1), na ausência e na presença de Si (1,29 mmol L-1) no tomat... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: A consequence of ammonium (NH4+) toxicity is the decrease in cytokinins (CKs) content. However, the supply of CK in the nutrient solution, in trans-zeatin (tZ) form, can alleviate NH4+ toxicity, and CK synthetic 6-benzyladenine (BA), with lower cost, has not yet been studied on the NH4+ toxicity. Similarly, silicon (Si), which is a beneficial element known to relieve stresses, also alleviates NH4+ toxicity. The objective was to verify if the relief of NH4+ toxicity by Si is dependent on the increase of the CKs content in tomato cv Micro-Tom (MT), the effects of Si on the transgenic tomato MT CKX2 (CKs deficient) submitted to NH4+ toxicity, and if the growth regulator 6-benzyladenine (BA) alleviates NH4+ toxicity in tomato MT. For this, five experiments were carried in tomato, with treatments application in nutrient solution. In experiment with NH4+ concentrations between 1.25 and 7.5 mmol L-1, 5.9 mmol L-1 caused NH4+ toxicity, with shoot dry weight 10% decrease. In experiment with Si concentrations between 0.2 and 0.8 mmol L-1, via potassium silicate (SiK) or stabilized silicic acid (ASiE), NH4+ toxicity was not alleviated. In the experiment with Si concentrations between 1 and 2.5 mmol L-1, via SiK, the concentration of 1.29 mmol L-1 alleviated NH4+ toxicity. In experiment with N in NO3- or NH4+ forms (5.9 mmol L-1), in absence and presence of Si (1.29 mmol L-1) in MT tomato, Si decreased CKs content in root and increase in shoot, independent of the N form. In same experime... (Complete abstract click electronic access below) / Doutor

Typewritten Includes bibliographical references

[Typewritten] Includes bibliographical references.

Trifolium ambiguum (Caucasian clover) is being released in New Zealand for use in areas where growth of T. repens (white clover) is marginal. Although closely related to T. repens, T. ambiguum has unique and highly specific nodulation requirements and as rhizobial strains capable of effectively nodulating T. ambiguum are not naturally found in New Zealand soils, they must be introduced with the seed. Rhizobium leguminosarum bv. trifolii strains such as ICC105 form effective nodules on T. ambiguum but ineffective (Fix⁻) nodules on T. repens. The T. repens nodules nevertheless develop normally and contain bacteroids. R. l. bv. trifolii strains that are effective on T. repens such as NZP561, fail to nodulate T. ambiguum. As the host-specific nitrogen fixation defect of Caucasian clover rhizobia on T. repens has potentially adverse agronomic implications, the genetic basis for this Fix⁻ phenotype was investigated. Rhizobium leguminosarum bv. trifolii strain ICC105 was converted to Fix⁺ on T. repens by the introduction of an 18-kb fragment of DNA from a white clover rhizobial strain (NZP514) symbiotic plasmid. This fragment contained several nif and fix genes, including nifHDKEN, fixABCX, nifA, nifB, fdxN and fixU. Tn5 mutation of these white clover rhizobial genes demonstrated that most were required to impart the Fix⁺ phenotype on T. repens to ICC105, with the exception of nifA. Mutagenesis of the ICC105 nifA gene and subsequent complementation with various combinations of the white clover rhizobia nif/fix genes as well as transcriptional lacZ fusion studies of the ICC105 nifA and nifH genes demonstrated that ICC105 nifA is expressed and functional during the ineffective nodulation of T. repens and able to activate expression of nifHDKEN and fixABCX operons derived from white clover rhizobium but not from ICC105. Sequence analysis and comparison of the intergenic region between the divergently transcribed nif/fix operons revealed a conserved 111-bp region found between the nifH/fixA promoters of Caucasian clover rhizobia, but not in white clover rhizobia. Attempts to modify this region in ICC105 failed in creating a strain which was Fix⁺ on T. repens; however recombination of the nifHD/fixAB region from a white clover rhizobium into the ICC105 genome produced several strains with a �swapped� nitrogen fixation phenotype (i.e. Fix⁺ on T. repens and Fix⁻ on T. ambiguum). A hypothesis was therefore proposed by which differences in the nifH/fixA promoter regions of Caucasian clover rhizobia and white clover rhizobia modulate the expression of the upstream genes in response to the particular plant host they are nodulating. The incompatibility between the symbiotic plasmid of R. l. bv. trifolii ICC105 and the white clover rhizobium symbiotic plasmid cointegrate, pPN1, was also investigated and potential regions of each plasmid involved in this incompatibility were identified. The research presented in this thesis has contributed to the genetic knowledge of the nitrogen fixation genes, and regulation of these genes in R. l. bv. trifolii. It has also provided progress towards the goal of creating a suitable inoculant strain for T. ambiguum that is able to fix nitrogen in symbiosis with both T. repens and T. ambiguum.

Bibliography: leaves 189-210 / xxxiv, 210 leaves : ill ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Agricultural Biochemistry, 1987

Bibliography: leaves 153-179. / xvi, 179 leaves : ill. (some col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Annual species of Medicago, or medics, are important pasture legumes in the neutral to alkaline soils of southern Australia but their nodulation and nitrogen fixation processes are retarded by soil nitrate. This study ascertains whether an observed tolerance to nitrate among medic species can be substantiated, and attempts to understand the underlying factors responsible. / Thesis (Ph.D.)--University of Adelaide, Dept. of Plant Science, (1995)

Bibliography: leaves 153-179. Annual species of Medicago, or medics, are important pasture legumes in the neutral to alkaline soils of southern Australia but their nodulation and nitrogen fixation processes are retarded by soil nitrate. This study ascertains whether an observed tolerance to nitrate among medic species can be substantiated, and attempts to understand the underlying factors responsible.

Although legumes have been widely studied for their nitrogen-fixing ability, it is uncertain to what extent legume cover crops achieve their nitrogen-fixing potential under the climatic conditions encountered in western Oregon. Furthermore, it is unknown what factors control the proportions of legume cover crop N that are either sequestered into soil organic matter, or that contribute to the N requirements of the following summer crop. Soil was sampled in mid-September 1997, after harvest of a summer broccoli crop, from plots located at the North Willamette Research and Extension Center, Aurora, Oregon. Soil was sampled from main plots that had been either winter cover cropped with red clover (LN��� and LN���) or fallowed during the winter period (FN��� and FN���), and specifically from sub-plots in which the following summer crop had received either zero (N���) or an intermediate (N���) rate of N fertilizer as urea. Levels of total organic carbon (TOC), total Kjeldahl nitrogen (TKN), and readily mineralizable C and N were measured in both whole soil samples and in different aggregate-size classes (<0.25, 0.25-0.5 0.5-1.0, 1.0-2.0, and 2-5mm) prepared by dry sieving the soil. Aggregate size-class distribution was not affected by the cover crop treatment. Although there was no significant effect of cover crop treatment on either TKN or TOC levels in whole soil samples, TOC levels were consistently higher in the small aggregate size-classes <1 mm of the fallow than the legume treatment. There was a significantly higher level of mineralizable C in the <0.25 mm size class of the legume than the fallow treatment. There was a trend for the level of mineralizable N to be greater in soil from the legume than the fallow treatment. However, N fertilizer had a significant positive effect on the level of readily mineralizable N in both fallow and legume cover-cropped treatments, it had a negative effect on TKN levels among all aggregate-size classes. There were differences in the levels of mineralizable N measured among the aggregate-size classes, and immobilization of N between 20 and 40 days of incubation also differed among the aggregate-size classes. / Graduation date: 1999

Thesis (Dr. rer. nat.)--Philipps-Universität Marburg, 2002. / Title from PDF t.p. (viewed on Apr. 24, 2007). Includes bibliographical references (p. 143-163).