Depending on the previous research on LDHA gene silencing in Rhizopus oryzae CCUG 28959 through introduction of siRNA, a integral vector was constructed by inserting two copies of LDHA gene (by PCR cloning) in a fashion that it can express hpRNA in the transformed fungi, which will trigger the post transcriptional degradation of targeted mRNA through RNA degradation pathway which is known to be quelling in fungi.The vector was successfully designed with the LDHA gene, transformed in to the host organism, and also transferred to its progeny. This helps in maintaining stability of the transformed cell lines. This created vector will be advantageous at this point when compared to the use of siRNA for gene silencing, which is not a stable way. In the future, this vector can be used for down regulating other genes of interest in R. oryzae and can also be used for studying its effect on other metabolic pathways.In this study, Hygromycin resistance to the R. oryzae CCUG 28959 was shown at levels up to 1000 μg/ml, which has not been reported previously. / Program: MSc in Resource Recovery - Industrial Biotechnology

RNA silencing with direct delivery of siRNA has been used to suppress ldhA gene expression in filamentous fungus Rhizopus oryzae. Here, for the first time we show that, introducing small interfering RNA which consequently forms silencing complexes can alter the gene expression and we report a significant reduction of lactic acid production for isolates containing short (25 nt) synthetic siRNA. In all samples lactic acid production was reduced comparing with wild types. The average concentration of lactic acid production by Rhizopus oryzae during batch fermentation process where glucose has been used as a sole carbon source, diminished from 2.06 g/l in wild types to 0.36 g/l in knockdown samples which signify 5.7 times decrease. Interestingly, the average concentration of ethanol production was increased from 0.38 g/l in wild types to 0.45 g/l in knockdown samples. In some samples we were able to report even a 10 fold decrease in lactic acid production. Since R.oryzae is capable to assimilate a wide range of carbohydrates hydrolysed from lignocellulosic material in order to produce many economically valuable bulk material such as ethanol, these results suggest that RNA silencing is a useful method for industrial biotechnology to be applied in fungus Rhizopus oryzae in order to trigger the metabolism and gene expression toward a desired product.

The maximum potential of biorefineries cannot be achieved without the valorisation of their residues. The two main residues from wheat biorefineries, bran and wet distiller's grains and solubles (WDGS), have a projected production of 7 and 3 million tonnes/year respectively by 2025 just in the European Union. These residues can be mixed to form moist animal feed. However, the product can undergo growth of contaminating fungi. This bio-deterioration causes significant losses and represents a hazard for the animals. Currently, commercial preservatives (from the petrochemical industry) are added to prevent bio-deterioration but these add to the production cost. The research reported in this thesis was focused on the utilisation of solid state bioprocessing (SSB) to prevent the bio-deterioration of the moist feed. The method is based on the inhibition of contaminating fungi by an edible fungus, R. oryzae, considered safe for animal consumption which is a lactic acid producer. This fungus is known to produce very dense mycelia causing significant oxygen transfer limitations and this, together with the reduction in pH and substrate available for contaminating fungi, was explored as a potential mechanism to bio-preserve the moist feed. SSB, has been targeted as a key technology for the treatment of agro-industrial solid residues. However, the measurement of parameters in SSB is very complicated, hampering the development of the technology. Consequently, methods for the measurement of pH and growth in SSB were also studied. The measurement of pH is normally performed in extract solutions but, although widely used, the method has not been standardised. There are many extraction variables, such as contact time, type of solids and solvent, solid:water ratio and agitation velocity, involved in the measurement. Experiments revealed that changes in the extraction conditions affect pH readings. The degree of impact depends upon the variable but results presented in this thesis clearly highlight the importance of providing a precise and comprehensive report of the extraction conditions. For the estimation of growth, a method based on digital imaging analysis (DIA) was developed in this work. DIA is a non-destructive, quick and simple method, which uses computational analysis of digital images to measure areas and colour changes on a surface. The technique provided data that allowed an objective comparison of fungal colonies on plates, making it of higher quality than simple visual evaluation. It was determined that C*Traffordgold, the model moist feed used in this research, has starch and moisture contents of 10% and 50% respectively. Bio-deterioration is caused by indigenous organisms in the bran and is observable after only 2 days of incubation at 20°C. R. oryzae was able to bio-preserve the material for at least a month. This is a very promising result since preservative treated C*Traffordgold shows considerable bio-deterioration after just 2 weeks. DIA was used for the estimation of R. oryzae growth at different temperatures, moisture contents and inoculum sizes. The fungus was able to grow at temperatures between 15° and 37°C, with optimum growth at 30°C. An increase in the moisture content resulted in faster growth of the fungus and it was determined that a minimum inoculum size of 103 spores/gC*Traffordgold is necessary to avoid bio-deterioration. The bio-preservation is a result of the reduction of substrate and oxygen available for contaminating microorganisms. Studies revealed that lactic acid does not inhibit growth of contaminating fungi even at pH 4. On the other hand, R. oryzae showed radial growth rates up to 6 times faster than those from contaminating cultures. The fungus is able to surround the competitor colony and 'enclose' it. The formation of a fungal barrier limits the oxygen available for the undesired colony, hampering its growth. It was estimated that by implementing the bio-preservation method a wheat biorefinery producing 180,000 tpa of moist feed could save circa 500,000 USD per annum. Integration of residue processing in biorefineries is necessary to make them sustainable. The application of SSB for bio-preservation could enhance the overall value of wheat biorefineries and simultaneously reduce dependency on the petrochemical industry.

ABSTRACT PURIFICATION AND CHARACTERIZATION OF HEXOKINASE ISOENZYMES FROM Rhizopus oryzae Dedeoglu, Didem MS., Department of Biotechnology Supervisor: Prof.Dr. Haluk Hamamci Co-supervisor: Dr. Seyda A&ccedil / ar February 2007, 116 pages Glycolysis is the central metabolic pathway for living organisms. Its regulation is important for the yield of the end products which are industrially important. These end products, like lactic acid produced by Rhizopus oryzae, are industrially important. Rhizopus oryzae is a filamentous fungus producing lactic acid and ethanol. The lactic acid yield of R. oryzae is low (&amp / #61566 / 70 %) compared to that of lactic acid bacteria (&amp / #61502 / 95 %) still it is noteworthy because R. oryzae produces only the L (+) form of lactic acid which can be metabolized in the human body. The yield of an industrial process should be high for the feasibility of the production of a particular product. If a way can be found increase the flux through the glycolysis the yield of lactic acid may increase as well. Keeping this in mind we wanted to focus on the first step of glycolysis, hexokinase of R. oryzae. Hexokinase catalyzes the reaction that converts glucose to glucose-6-phosphate. In this study for the first time the two isoenzymes of hexokinase of R. oryzae were purified and characterized by biochemically and kinetically Hexokinase has two isoenzymes. The purified enzymes (isoenzymes1 &amp / isoenzymes2) obeyed Michealis-Menten Kinetics. The Km value of purified isoenzyme 1 is 0.16 mM and isoenzyme 2, 0.21 mM at pH 7.70 for glucose. The Km value of isoenzyme1 for fructose was 28.8 mM. Essentially isoenzyme 2 can not utilize fructose. None of the isoenzymes were inhibited by trehalose-6-phophate.The monomer moleculer weight of isoenzymes were estimated SDS PAGE analysis. There were two different values for molecular weight of isoenzmye 1 / 62.9 and 42.5 kDa and two values for isoenzyme 2 / 56.2 and 41.6 kDa

Rhizopus oryzae is a filamentous fungus, which can produce high amounts of L(+)-lactic acid and produces ethanol as the main by-product. In an effort to understand the pyruvate branch point of this organism, fermentations under different inoculum and glucose concentrations were carried out. At low inoculum size (1x103 spores ml-1), high amount of lactate (78 g l-1) was produced, whereas high ethanol concentration (37 g l-1) was obtained at high inoculum sizes (1x106 spores ml-1). Decreasing working volume increased lactate production significantly at high inoculum sizes (1x105 and 1x106 spores ml-1), but did not influenced the physiology at low inoculum sizes (1x103 and 1x104 spores ml-1). In shake flask cultures, at low initial glucose concentrations biomass yield was high and lactate and ethanol yields were low. Higher lactate and ethanol and lower biomass yields were obtained by increasing the initial glucose concentrations. In alginate immobilized, semi-continuous cultures with cell retention, glucose level in the medium was kept at low values. Like in shake flask cultures, as the glucose concentration decreased lactate and ethanol yields decreased and biomass yields increased. Increasing the glucose concentration by a pulse of glucose caused increases in branch point enzyme activities, as well as in concentrations of the metabolites. In fed batch cultures higher biomass yield (0.25 g DCW g glucose-1) could be obtained. Lactate dehydrogenase was influenced by the inoculum size and glucose concentration more than pyruvate decarboxylase and alcohol dehydrogenase. It showed higher activity at lactate producing fermentations. Unlike lactate dehydrogenase, pyruvate decarboxylase and alcohol dehydrogenase showed high activity even at low glucose concentrations.

In many organisms, trehalose protects against several environmental stresses, such as heat, desiccation and salt, probably by stabilizing protein structures and lipid membranes. Trehalose-6-phosphate synthase 1 (TPS1) is a subunit of trehalose synthase complex in fungi / it plays a key role in the biosynthesis of trehalose. In this study, a TPS1 gene fragment in R. oryzae was cloned successfully by PCR with primers designed according to eight hypothetical proteins found from BLAST search which was performed by using S. cerevisiae TPS1 gene template. The full length of R. oryzae TPS1 gene (designated RoTPS1) was attained by RTPCR with primers specific to the 3&amp / #8242 / and 5&amp / #8242 / end of the RoTPS1 cDNA. The RoTPS1cDNA was composed of 2505 bps encoding a protein of 834 amino acids with a molecular mass of 93.8 kDa. The amino acid sequence has relatively high homology with the TPS1s of several other organisms. RoTPS1 was further characterized by transformation into S. cerevisiae tps1 mutant. In galactose media, the growth curves of wild type, tps1 mutant and transformant S. cerevisiae cells had a comparable pattern in general, tps1 mutant reached to a higher maximum cell concentration compared to the others and wild type had a slightly lower specific growth rate compared to the tps1 mutant and transformed cells. Trehalose levels of transformant and wild type cells were increased up to 37 mg/gdw in the stationary phase.

v, 78 leaves : photo., graphs, tables ; 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 Entomology, Waite Agricultural Research Institute, 1978

Computational tools play an important role in the description of biological systems. Scientists describe and study structure, conformational changes and interactions between molecules in silico, often as a cheaper and faster alternative for biosynthesis. The simulated dynamic behavior in time of a molecular system is a straight forward source of information about substrate-enzyme interactions at the atomic level, and a powerful tool for the identification of molecular properties important in enzymatic reactions. Our study is focused on the computational investigation of structure and substrate specificity of hydrolases important in biotransformation. The computational work was performed in close collaboration with biochemists-experimentalists from Charles University and the Microbiological Institute of the Academy of Sciences of the Czech Republic. Hydrolases have great a potential in the chemoenzymatic synthesis of modified carbohydrates with regulated properties. Carbohydrates, as substrates of hydrolases, are important in normal functionality of many organisms. They have a dual role in immune response regulation: some carbohydrates (like GlcNAc and ManNAc) participate in activation and some (like GalNAc) in suppressing immunity; glycosidase deficiency is associated with a number of lysosomal disorders. We used homology modeling, computational docking and molecular dynamics simulation (MD) methods for the complex study of fungal hydrolases: alpha-galactosidase/alpha-N-acetylgalactosaminidase from Aspergillus niger; beta-N-acetylhexosaminidases (HEX) (from Aspergillus oryzae and Penicillium oxalicum); nitrilase from Aspergillus niger. Our structural study unambigously demonstrates that the enzyme encoded by genes variant A (aglA) from A. niger is able to accept alpha-N-acetylgalactosamine as its substrate and explains structural features responsible for its specificity. Homology models of HEXs from P. oxalicum and A. oryzae were built and compared. Homology models were used to study the role of protein glycosylation, disulfide bonds, dimer formation and interaction with natural and modified substrates. Model of nitrilase from Aspergillus niger helped to analyze multimer formation.

Submitted by Marco Antônio de Ramos Chagas (mchagas@ufv.br) on 2017-06-29T18:34:52Z No. of bitstreams: 1 texto completo.pdf: 1000132 bytes, checksum: f8825fd96a75440247eb51ddedd55c61 (MD5) / Made available in DSpace on 2017-06-29T18:34:52Z (GMT). No. of bitstreams: 1 texto completo.pdf: 1000132 bytes, checksum: f8825fd96a75440247eb51ddedd55c61 (MD5) Previous issue date: 2016-02-17 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Dois experimentos (Exp. 1 e Exp. 2) foram conduzidos em condições de campo para determinar o desenvolvimento da brusone em espigas, bem como a performance fisiológica e produtiva das cultivares BR-18 (moderadamente resistente) e Guamirim (suscetível) inoculadas com Pyricularia oryzae e tratadas (+F) ou não (‒F) com o fungicida epoxiconazole (13,3%) + pyraclostrobina (5%). Relativo a Guamirim ‒F, BR-18 ‒F (efeito da resistência) resultou em redução de 44 e 64% na incidência final e severidade final, respectivamente, no Exp. 1, e 3 e 49%, respectivamente, no Exp. 2. Para a Guamirim +F (efeito do fungicida) houve redução de 65 e 77% na incidência final e severidade final, respectivamente, no Exp. 1, e 64 e 95%, respectivamente, no Exp. 2. Similarmente, houve redução maior que 75 % na taxa temporal de progresso no tratamento combinando a aplicação do fungicida e resistência de hospedeiro. Resultados obtidos na análise de regressão indicaram que a severidade encontrada nas espigas e folhas durante o período de 10-14 dias após a antese (daa) proporcionou uma maior perda de produtividade comparado a severidade encontrada aos 18-22 daa, e que a severidade da brusone nas espigas possui maior efeito negativo comparado a severidade encontrada nas folhas. Relativo a Guamirim ‒F, houve aumento de 0.3 e 16 % na produtividade dos grãos para BR-18 ‒F, 20 a 61% para Guamirim +F e 26 e 83% para BR-18 +F nos Exp. 1 e Exp. 2, respectivamente. Os tratamentos envolvendo aplicação do fungicida e cultivar resistente manteve a integridade das folhas (baseado em HAD, HLAI, HAA e HRI) e performance fotossintética (baseado em Fv/Fm, Fm, Y(II), e Y(NPQ)) das espigas e folhas em relação ao tratamento cultivar Guamirim ‒F. Em conclusão, os resultados do presente estudo sugerem que a integração do tratamento com fungicida e resistência de cultivar como prática de manejo para o controle da brusone em espigas. Adicionalmente, dois experimentos foram conduzidos em condições de casa de vegetação para avaliar as alterações associadas com a produção e particionamento de fotoassimilados entre a espiga e a folha bandeira em plantas de trigo infectadas com P. oryzae. Ambos experimentos foram inoculados aos 10 e 20 daa com suspensão de esporos de P. oryzae. Os resultados demonstraram uma redução dos parâmetros de fluorescência da clorofila a (Fm, Fv/Fm YII and Y(NO)) em folhas bandeiras e espigas infectadas associada a menor concentração de clorofila a + b, carotenoides e redução da capacidade de fixação do CO2 pela RuBisCO em folhas bandeiras infectadas. Em folhas bandeiras e grãos obtidos de espigas infectadas, houve redução na concentração de açúcares solúveis com um aumento da razão da concentração de hexoses sobre sacarose em folhas bandeiras. Em folhas bandeiras, houve menor atividade da sacarose fosfato sintase (SPS) e menor expressão do gene sacarose sintase associadas ao aumento da expressão e atividade das invertases. Estas alterações relacionadas a síntese e degradação da sacarose sugerem uma condição dreno dos tecidos foliares infectados. No estágio final de infecção ocorreu uma redução da concentração de amido nos grãos e aumento da sua concentração em folhas bandeiras. Adicionalmente, houve redução na atividade e expressão da ADP-glicose pirofosforilase associada com a menor expressão dos genes β- e α-amilase em folhas bandeiras e espigas. Em conclusão, os efeitos negativos da brusone na qualidade e produtividade dos grãos em trigo podem ser associados com alterações na produção e particionamento de carboidratos durante o processo de formação dos grãos. / Two field experiments (Exp. 1 and Exp. 2) were carried out to evaluate the spike blast development as well as the physiological performance and grain yield of wheat cultivars BR-18 (partially resistant) and Guamirim (susceptible) inoculated with Pyricularia oryzae and treated or untreated with the fungicide 13.3% epoxiconazole + 5% pyraclostrobin. Relative to Guamirim-untreated, BR-18-untreated (resistance alone) led to 44 and 64% control of final incidence and severity, respectively, in Exp. 1, and 3 and 49% control, respectively, in Exp. 2. Guamirim-treated (fungicide alone) led to 65% control of incidence and 77% control of severity in Exp. 1, and 64% control of incidence and 95% control of severity in Exp. 2. Similarly, there was reduction higher than 75 % in the temporal rate of spike blast progress when host resistance and fungicide were combined. Results from regression analyses indicated that spike and leaf blast severity at 10-14 days after anthesis resulted in greater yield losses (highest negative slope) than severity at 18 to 22 days after anthesis, and that spike blast severity had a greater negative effect on yield than leaf blast severity. Relative to Guamirim-untreated, there was a 0.3 and 16% increase in mean yield for BR-18-untreated (resistance alone), 20 and 61% increase for Guamirim treated (fungicide alone), and 26 and 83% for BR-18 treated (moderate resistance + fungicide) in Exp. 1 and 2, respectively. By virtue of their effects on blast severity, fungicide application and cultivar resistant resulted in higher measures of leaf health (mean HAD, HLAI, HAA and HRI) and photosynthetic performance (based on F v /F m , F m , Y(II), and Y(NPQ)) of both spikes and leaves than the untreated susceptible reference treatment. Results from this study suggesting that the integration of these strategies may be the best approach for managing spike blast and useful for future efforts to develop crop loss models and management guidelines for wheat blast. Additionally, two experiments were carried out in greenhouse conditions to assess the changes associated with photoassimilates production and their partitioning in source-sink relationship on flag leaves and spikes of wheat plants infected with Pyricularia oryzae. Flag leaves and spikes were inoculated at 10 days after anthesis (daa) (Exp. 1) and at 20 daa (Exp. 2) with a conidial suspension of P. oryzae. There was an impairment on chlorophyll a fluorescence parameters (analyzed by F m , F v /F m YII and Y(NO)) on the infected flag leaves and spikes coupled with reduced concentrations of chlorophyll a + b and carotenoids as well as lower capacity of CO 2 fixation by RuBisCO in the infected flag leaves. In these leaves and grains obtained from the infected spikes, there were lower concentration of soluble sugars and an increase on the hexoses to sucrose ratio on the flag leaves. In the infected flag leaves, there was a lower sucrose phosphate synthase (SPS) activity and lower expression of sucrose synthase (Susy) gene coupled with higher expression and activity of acid invertases. These alterations, associated with synthase and degradation of sucrose, suggestss a status sink in the infected flag leaves. At advanced stages of fungal infection, the concentration of starch was reduced on grains whereas on the infected flag leaves its concentration was kept elevated. There were reduction on the activity of ADP-glucose pyrophosphorylase and on the expression of ADP-glucose pyrophosphorylase genes and down regulation of β- and α-amylase expression at late stages of fungal infection on flag leaves and spikes. In conclusion, the greatest effect of blast on both grains quality and yield can be associated with alterations in the production and partitioning of carbohydrates during the grain filling process.

Submitted by Reginaldo Soares de Freitas (reginaldo.freitas@ufv.br) on 2016-05-31T09:26:57Z No. of bitstreams: 1 texto completo.pdf: 1453980 bytes, checksum: a906f0c2ee1673a4173cbe5af072a89a (MD5) / Made available in DSpace on 2016-05-31T09:26:57Z (GMT). No. of bitstreams: 1 texto completo.pdf: 1453980 bytes, checksum: a906f0c2ee1673a4173cbe5af072a89a (MD5) Previous issue date: 2013-07-05 / Conselho Nacional de Desenvolvimento Científico e Tecnológico / A escaldadura, causada pelo fungo Microdochium oryzae, é uma das principais doenças do arroz (Oryza sativa) no Brasil. Considerando que até o momento, informações sobre a interação arroz-M. oryzae são escassas, buscou-se, neste trabalho investigar a fotossíntese, o metabolismo antioxidativo e as respostas de defesa de plantas de arroz da cultivar Primavera, supridas ou não com silício (Si) durante o processo infeccioso de M. oryzae. No primeiro estudo, uma abordagem a fim de avaliar a diversidade de eventos que ocorrem próximo à área infectada numa mesma folha durante a infecção por M. oryzae foi realizada, a fim de contribuir para um maior entendimento na dinâmica fotossintética durante a interação planta- hospedeiro. Para esta finalidade, foi realizada a avaliação de parâmetros e imagens de fluorescência da clorofila a em diferentes áreas próximas a lesão, associando-as, às trocas gasosas e a avaliação dos pigmentos fotossintéticos em plantas de arroz inoculadas ou não inoculadas com M. oryzae. Em plantas não inoculadas com M. oryzae os valores da fotossíntese (A), da condutância estomática (gs) e da taxa transpiratória (E) foram maiores em relação às plantas inoculadas, evidenciando o efeito negativo causado pelo fungo nas trocas gasosas, principalmente em A. A utilização da energia para os processos fotossintéticos e a capacidade de dissipação do excesso de energia na maquinaria fotossintética demonstrados pelos parâmetros de fluorescência de imagem da clorofila a foi comprometida durante a infecção, reduzindo o rendimento fotoquímico e induzindo a inibição do aparato fotossintético nas áreas lesionadas, evidenciando que a infecção tinha efeito local sobre A. Houve diminuição das áreas verdes na superfície do tecido foliar, ocasionado pela expansão das lesões e aumento de tecido necrótico. As concentrações de pigmentos fotossintéticos diminuíram significativamente com o progresso da escaldadura o que limitou a absorção da radiação fotossinteticamente ativa. No segundo estudo, buscou-se investigar a atividade das enzimas antioxidativas ascorbato peroxidase (APX), peroxidase (POX), catalase (CAT), superóxido dismutase (SOD) e glutationa redutase (GR), os danos causados à membrana celular através da concentração de aldeído malônico (MDA), as concentrações de peróxido de hidrogênio (H2O2) e de pigmentos fotossintéticos, bem como trocas gasosas em folhas de plantas de arroz durante o processo infeccioso de M. oryzae. O progresso da doença promoveu redução da A, gs e E. Houve também incrementos na concentração interna de CO2 e redução na concentração de pigmentos fotossintéticos ocasionados pela expansão das lesões, comprometendo a absorção da radiação fotossinteticamente ativa e limitando a fotossíntese. As atividades das enzimas envolvidas no sistema antioxidativo nas plantas de arroz infectadas por M. oryzae aumentaram na tentativa de impedir o acúmulo de H2O2, principalmente APX, POX e GR, não sendo, entretanto, eficientes na remoção do excesso de H2O2, resultando em dano oxidativo. As concentrações de MDA nas plantas inoculadas mantiveram-se elevadas no final do processo infeccioso, como resultado da peroxidação lipídica. No terceiro estudo, buscou-se, investigar o efeito do Si sobre as trocas gasosas, a eficiência fotoquímica do fotossistema II e a concentração de pigmentos fotossintéticos em plantas de arroz infectadas por M. oryzae. Para esta finalidade plantas de arroz da cultivar Primavera foram cultivadas em solução nutritiva contendo 0 ou 2 mmol L-1 de Si e não inoculadas ou inoculadas com M. oryzae. A infecção por M. oryzae reduziu o rendimento fotossintético, o qual esteve associado com a menor concentração de pigmentos fotossintéticos nas folhas. Na presença de Si, a atividade fotossintética e a eficiência de utilização da energia luminosa e sua conversão em energia química foram potencializados, conforme demonstrado pelos parâmetros de fluorescência de imagem da clorofila a, independente da inoculação com M. oryzae, confirmando assim, que o Si é um elemento importante no rendimento fotossintético em plantas de arroz infectadas por M. oryzae. No quarto estudo, buscou-se, investigar o papel do Si na resistência de plantas de arroz infectadas por M. oryzae. Para esta finalidade, plantas de arroz da cultivar Primavera foram cultivadas em solução nutritiva contendo 0 ou 2 mmol L-1 de Si e inoculadas com M. oryzae. A concentração foliar de Si aumentou nas plantas supridas com esse elemento em relação às plantas não supridas o que contribui para reduzir a expansão das lesões. A extensão dos danos celulares em resposta a infecção por M. oryzae foi reduzida nas plantas supridas com Si, evidenciado pelos menores valores da concentração de MDA. Maiores concentrações de compostos fenólicos solúveis totais (CFST) e de derivados da lignina-ácido tioglicólico (DLATG) nos tecidos foliares das plantas supridas com Si, contribuíram para a resistência à escaldadura. Maiores atividades das enzimas peroxidases (POX), polifenoloxidases (PFO), fenilalanina amônia-liases (FAL) e lipoxigenases (LOX), mas não de quitinases (QUI) e β-1,3-glucanases (GLU), nos tecidos foliares das plantas de arroz supridas com Si foram importantes para a resistência à escaldadura. Em conclusão, os resultados do presente estudo evidenciam que o Si pode aumentar a resistência à escaldadura em plantas de arroz, melhorando o rendimento fotossintético e potencializando mecanismos bioquímicos de defesa ao invés de agir apenas como uma barreira física na tentativa de conter a penetração de M. oryzae. / The scald caused by the fungus Microdochium oryzae is a major disease of rice (Oryza sativa) in Brazil. Whereas until now, information on the interaction rice-M. oryzae are scarce, we sought in this paper to investigate photosynthesis, metabolism antioxidative and defense responses of rice plants of cultivar Primavera, or not supplied with silicon (Si) during the infection process of M. oryzae. In the first study, an approach to assess the diversity of events that occur near the infected area on one sheet when the infection with M. oryzae was carried out in order to contribute to a greater understanding of the dynamics during photosynthetic plant-host. For this purpose, we analyzed the fluorescence parameters and images of chlorophyll a in different areas around the injury, associating them, gas exchange and evaluation of photosynthetic pigments in rice plants inoculated or not with M. oryzae. Not in plants inoculated with M. oryzae values of photosynthesis (A), stomatal conductance (gs) and transpiration rate (E) were higher than those inoculated plants, indicating the negative effect caused by the fungus in gas exchange, especially in A. The use of energy for photosynthetic processes and dissipation of excess energy in the photosynthetic machinery demonstrated by fluorescence parameters and images of chlorophyll a was compromised during the infection, reducing the yield and photochemical induced inhibition of the photosynthetic apparatus in the injured areas, showing that the infection had local effect on A. There was decrease in the surface areas of the green leaf tissue, caused by the expansion of lesions and necrotic tissue augmentation. The photosynthetic pigments decreased significantly with the progress of scalding which limited the absorption of photosynthetically active radiation. In the second study, we sought to investigate the activity of antioxidant enzymes ascorbate peroxidase (APX), peroxidase (POX), catalase (CAT), superoxide dismutase (SOD) and glutathione reductase (GR), damage to the cell membrane through concentration malondialdehyde (MDA), the concentrations of hydrogen peroxide (H2O2) and photosynthetic pigments as well as gas exchange in leaves of rice plants during the infectious process of M. oryzae. The progress of the disease promoted reduction of the A, gs and E. There were also increases in internal CO2 concentration and reduction in the concentration of photosynthetic pigments caused by the expansion of lesions affecting the absorption of photosynthetically active radiation and limiting photosynthesis. The activities of enzymes involved in the antioxidant system in rice plants infected by M. oryzae increased in an attempt to prevent accumulation of H2O2, especially APX, POX and GR is not, however, efficient removal of excess H2O2, resulting in oxidative damage. The concentration of MDA in the inoculated plants remained high at the end of the infection as a result of lipid peroxidation. In the third study, we sought to investigate the effect of Si on gas exchange, photochemical efficiency of photosystem II and the concentration of photosynthetic pigments in rice plants infected by M. oryzae. For this purpose the rice plants Primavera were grown in nutrient solution containing 0 or 2 mmol L-1 of Si and not inoculated or inoculated with M. oryzae. Infection with M. oryzae reduced the photosynthetic yield, which was associated with the lowest concentration of photosynthetic pigments in leaves. In the presence of Si, photosynthetic activity and efficiency of utilization of light energy and its conversion into chemical energy were potentiated, as demonstrated by f fluorescence parameters and images of chlorophyll a, regardless of inoculation with M. oryzae, thus confirming that Si is an important element in quantum yield in rice plants infected by M. oryzae. In the fourth study, we sought to investigate the role of Si in resistance of rice plants infected by M. oryzae. For this purpose, the rice plants Primavera were grown in nutrient solution containing 0 or 2 mmol L-1 of Si and inoculated with M. oryzae. The Si concentration increased in the leaf of plants supplied with this element in relation to unmet plants which contributes to reduce the spread of lesions. The extent of cellular damage in response to infection with M. oryzae was reduced in plants supplied with Si, evidenced by lower values of MDA concentration. Higher concentrations of total soluble phenolics (TSP) and derivatives of lignin-thioglycolic acid (DLATG) in the leaves of plants supplied with Si, contributed to resistance to scald. Major activities of the enzymes peroxidase (POX), polyphenol oxidases (PPO), phenylalanine ammonia-lyase (PAL) and lipoxygenase (LOX) but not chitinase (CHI) and β-1, 3- glucanases (GLU) in leaf tissues of rice plants were supplied with Si important for resistance to leaf scald. In conclusion, the results of this study indicate that the Si can increase resistance to scald in rice plants, improving performance and enhancing photosynthetic biochemical defense mechanisms rather than merely acting as a physical barrier in an attempt to contain the penetration of M . oryzae.