Selenium (Se) is an essential element for human and livestock with antioxidant and anticancer characteristics. Although Se is not an essential element for plants, it has been reported that it can improve plant growth. This experiment was conducted at the Isfahan University of Technology in winter 2010. The experiment was factorial based on a completely randomized design (CRD) with 4 replications. Se was added to nutrient solution in 4 concentrations 2, 4, and 6 mg/l sodium selenite (Na2SeO3). Root volume, fresh and dry weights of shoots and roots, number and weight of fruits, chlorophyll content and photosynthesis traits (photosynthesis rate, stomata internal carbon dioxide (CO2) concentration, stomata conductance) were measured. Results showed that Se increased root dry weight. Fresh and dry weights of shoot increased in the 2 mg/l Se treatment and decreased at the higher level of Se. Chlorophyll content and photosynthesis rate were not affected by Se. Stomata internal CO2 concentration and stomata conductance decreased by Se addition. Overall, Se at 2 mg/l application rate was effective in some physiological characteristics of cucumber.

A indução de resistência em plantas contra fitopatógenos é um método alternativo de controle de doenças, o qual envolve a ativação de mecanismos de resistência latentes da planta. Hoje no mercado existem poucos produtos que atuam segundo este princípio. Na busca de novas moléculas que possam ser utilizadas em campo, diversos compostos de origem microbiana, com capacidade de estimular uma ou mais respostas de defesa, já foram isolados e caracterizados. A Saccharomyces cerevisiae é uma levedura capaz de induzir resistência e elicitar respostas de defesa em algumas plantas. Com o objetivo de extrair da levedura um ou mais compostos capazes de induzir o acúmulo de fitoalexinas em cotilédones de soja e na proteção dessa leguminosa contra Microsphaera diffusa (agente causal do oídio da soja) e de pepino contra Colletotrichum lagenarium (agente causal da antracnose do pepino), células em suspensão foram autoclavadas. Os compostos assim extraídos foram inicialmente separados através de precipitação etanólica. Em seguida, foram realizadas cromatografias de troca iônica e de afinidade para separar as frações com maior poder elicitor das de baixo poder elicitor. A fração não adsorvida à resina DEAE-Celulose foi a que induziu maior acúmulo de fitoalexinas. No entanto, nenhum dos preparados testados foi capaz de conferir proteção a plantas de soja contra M. diffusa. Já no caso de pepino, plântulas tratadas com as frações resultantes da cromatografia de afinidade apresentaram reduções entre 50 e 70 % de área lesionada causada por C. lagenarium e aumento na atividade de peroxidases. Extratos incorporados à meio de cultivo não apresentaram efeito inibitório sobre o crescimento e esporulação de C. lagenarium. Com base nesses resultados, concluímos que existe na parede da levedura compostos capazes de induzir resistência local em pepino contra C. lagenarium, sendo que pelo menos um destes compostos é um carboidrato, contendo provavelmente manana e glucosamina. / The acquired resistance of plants to pathogens is an alternative method to control diseases which includes the activation of resistance mechanisms in the plants. A few products already commercially available have their action based upon this mechanism. In the search for novel molecules that can be used under field conditions, many compounds from microbes with the ability to stimulate one or more defense responses were already isolated and characterized. Saccharomyces cerevisiae is an yeast with the ability to induce defense responses and resistance in some plants. A suspension of cells from the yeast was autoclaved with the purpose of extracting one or more compounds with the ability to induce the accumulation of phytoalexins in soybean cotyledons and to protect soybean plants against Microsphaera diffusa (causal agent of powdery mildew) and plants of cucumber against Colletotrichum lagenarium (causal agent of anthracnose). The compounds extracted by this method were separated using ethanolic precipitation. After this step, the fractions of higher elicitation activity were separated from those of lower one by using ion exchange cromatography and affinity cromatography. The non-adsorbed fraction to DEAE-Cellulose was the one that induced the highest accumulation of phytoalexins. However, none of the fractions were able to protect soybean plants from M. diffusa. In the case of cucumber, seedlings treated with the fractions from affinity chromatography were able to reduce disease symptoms caused by C. lagenarium by 50 to 70 % and to increase the activity of peroxidases. Extracts that were incorporated into growing media did exhibit any inhibitory effect on in vitro growth and sporulation of C. lagenarium. According to these results, it is possible to conclude that there are compounds in the cell walls of the yeast that are able to induce local resistance to C. lagenarium in cucumber and that at least one of these compounds is a carbohydrate that likely contains mannan and glucosamine.

Includes appendix containing journal publications co-authored by the author. Includes bibliographical references (leaves 130-151). Eighteen strains of Cucumber mosaic virus, including forteen from Australia, two from the USA, and two from Japan were used in this study.

Includes bibliographical references (leaves [102]-120). Studies the structure of the cucumber mosaic virus genome and the control of its expression.

Includes appendix containing journal publications co-authored by the author. / Includes bibliographical references (leaves 130-151). / xiii, 151 leaves : ill., photos ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Eighteen strains of Cucumber mosaic virus, including forteen from Australia, two from the USA, and two from Japan were used in this study. / Thesis (Ph.D.)--University of Adelaide, Dept. of Crop Protection, 1992

Bibliography: leaves 127-138. This thesis studies the minor double stranded RNAs (dsRNA) and single stranded RNAs (ssRNA) which are consistently associated with plants infected with Q strain of cucumber mosaic virus (Q-CMV). The investigations are focused on the structural elucidation of new RNAs which have been observed in single stranded and double stranded RNA profiles of Q strain of CMV.

Includes bibliographical references (leaves 108-123). Includes the paper: Stabilization of capsid structure and enhancement of immunogenicity of cucumber mosaic virus (Q strain) by formaldehyde / by R.I.B. Franki and N. Habili, originally published in Virology, v. 48, no. 2, 1972 The comparative studies carried out suggest that tomato aspermy virus and the Q strain of cucumber mosaic virus are sufficiently similar to be included in the same taxonomic group. Nevertheless, the two viruses are distinct and the present nomenclature should be retained.

Typescript (photocopy) Includes bibliographical references (leaves 84-94). Eight cucumovirus isolates were examined with respect to their host range, antigenic properties and nucleic acid composition.

Dissertation (Ph.D.)--Auburn University, 2009. / Abstract. Includes bibliographic references (p.72-81).

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