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Previous issue date: 2007-02-27 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / Rice is one of the most important cereals for the humanity, because it is primary source of
nutrition for more than half of the world s population. Nitrogen is the most important element
for plants and is predominantly present in aerated soils in the nitrate form. As a result of the
poor quality of the cultivated areas, the usage of nitrogen fertilizers intensified, contributing to
the increase of pollution, since this nutrient has high mobility in the soil. With the objective of
evaluating physiologic, biochemical and molecular mechanisms responsible for the efficiency
of the application of nitrogen in rice, experiments were conducted at the Soils Department of
Federal Rural University of Rio de Janeiro. Two rice varieties were used, Piaui (traditional
rice) and IAC-47 (improved rice). In the beginning, both varieties were cultivated in nutrition
solutions and submitted to treatments simulating the seasonal fluctuation of nitrate,
characteristic of the tropical region. Under this condition an evaluation was done in order to
define the soluble sugar levels, nitrogen fractions, and the Nitrate Reductase Activity (NRA)
as well as Glutamine Synthetase Activity. Piaui rice was more efficient in the acquisition and
usage of nitrogen compared to IAC-47, accumulating nitrate in its tissue during the initial
phase of growth for future consumption. Later, these same rice varieties were cultivated in a
growth chamber with the objective of studying the effect of increased nitrate concentrations
over nitrogen fraction levels, NRA, relative expression of genes for nitrate transporters
(NRT1 and NRT2) as well as a nitrate reductase (Nia2). From the results obtained it was
observed that the traditional rice variety contained less NRA, higher levels of nitrogen and
free amino-N. Further, traditional variety presented higher relative expression of the genes
which codify nitrate transporters of low affinity (NRT1) and those of high affinity (NRT2).
These plants seemed to adopt a differentiated control of NRA, because even having a higher
relative expression of the genes, the NRA maintained practically without influence from the
different concentrations of nitrate in the solution. In the last experiment, genes in the tips of
rice roots were identified, induced by different concentrations of nitrate (0.1 and 10 mM).
Several genes were sequenced, were the most important data was the subunit E1 of the
dehydrogenase pyruvate complex, and phosphofructokinase, suggesting the need for a better
understanding of the complexity of the interaction between carbon and nitrogen metabolism.
There were also found sequences homologous to the alpha actin, myosin, tropomyosin 1,
creatin kinase, and glyoxalase I genes. / O arroz ? um dos mais importantes cereais para o homem, porque ? fonte prim?ria na
alimenta??o de mais da metade da popula??o do mundo. As plantas necessitam de nitrog?nio
para seu desenvolvimento, sendo este presente em solos aerados, na forma de nitrato. Em
fun??o do desgaste das ?reas cultivadas, tem sido intensificada a utiliza??o de fertilizantes
nitrogenados, o que contribui para o aumento da polui??o, visto que, esse composto possui
grande mobilidade no solo. Objetivando-se avaliar os mecanismos fisiol?gicos, bioqu?micos e
moleculares respons?veis pela efici?ncia no uso de nitrog?nio em arroz foram conduzidos tr?s
experimentos no Departamento de Solos da Universidade Federal Rural do Rio de Janeiro,
com duas variedades de arroz, uma tradicional (Piau?) e outra melhorada (IAC-47).
Primeiramente, ambas as variedades foram cultivadas em solu??o nutritiva e submetidas a
tratamentos simulando o fluxo sazonal de nitrato, caracter?stico das regi?es tropicais. Nessa
condi??o, foram avaliados os teores de a??cares sol?veis, fra??es nitrogenadas e a atividade
das enzimas Nitrato Redutase (ANR) e Glutamina Sintetase. A variedade Piau? foi mais
eficiente na aquisi??o e uso do N quando comparada a IAC-47, acumulando nitrato em seus
tecidos durante as fases iniciais de crescimento. Depois, essas mesmas variedades foram
cultivadas em c?mara de crescimento para estudar o efeito de concentra??es crescentes de
nitrato sobre os teores das fra??es nitrogenadas, ANR e sobre o perfil de express?o relativa
dos genes dos transportadores de nitrato (NRT1 e NRT2) e da Nitrato Redutase (Nia2). Dos
resultados obtidos, foi observado que a variedade tradicional possui menor ANR, maiores
teores de nitrato e N-amino livre. Al?m disso, esta apresentou maior express?o relativa dos
genes que codificam os transportadores de nitrato de baixa (NRT1) e os de alta (NRT2)
afinidade, sendo esse na parte a?rea. Estas plantas pareceram adotar um controle diferenciado
da ANR, pois mesmo tendo maior express?o relativa desse gene, a atividade desta enzima se
mant?m praticamente sem sofrer influ?ncia das concentra??es de nitrato na solu??o. No
?ltimo experimento, foram identificados os genes induzidos por duas concentra??es de nitrato
(0,1 e 10 mM) em ?pices radiculares de arroz. Diversos genes foram seq?enciados, dentre
eles, destacou-se a subunidade E1 do complexo piruvato desidrogenase e fosfofrutoquinase,
indicando a necessidade de se melhor entender a complexidade da intera??o entre o
metabolismo de carbono e nitrog?nio. Foram encontradas tamb?m seq??ncias hom?logas aos
genes da alfa actina, miosina, tropomiosina 1, creatina cinase e glioxalase I.
| Identifer | oai:union.ndltd.org:IBICT/oai:localhost:tede/306 |
| Date | 27 February 2007 |
| Creators | Santos, Andr? Marques dos |
| Contributors | Souza, Sonia Regina de, Fernandes, M?nlio Silvestre |
| Publisher | Universidade Federal Rural do Rio de Janeiro, Curso de P?s-Gradua??o em Agronomia - Ci?ncia do Solo, UFRRJ, Brasil, Ci?ncias Agr?rias |
| Source Sets | IBICT Brazilian ETDs |
| Language | Portuguese |
| Detected Language | English |
| Type | info:eu-repo/semantics/publishedVersion, info:eu-repo/semantics/doctoralThesis |
| Format | application/pdf |
| Source | reponame:Biblioteca Digital de Teses e Dissertações da UFRRJ, instname:Universidade Federal Rural do Rio de Janeiro, instacron:UFRRJ |
| Rights | info:eu-repo/semantics/openAccess |
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