Study on the Sugar-Acid Ratio and Relevant Metabolizing Enzyme Activities in Navel Orange Fruits From Different Eco-Regions

Abstract

-The flavor quality of citrus fruits is largely determined by the sugar-acid ratio, but it remains uncertain how sugar-and/or acid-metabolizing enzymes regulate the sugar-acid ratio of navel oranges and further affect the fruit quality. In the present study, Robertson navel oranges (Citrus sinesis osb.) were collected from six representative habitats in three eco-regions of Sichuan, China. The changes in the sugar-acid ratio and the activities of sucrose phosphate synthase (SPS), sucrose synthase (SS), cytosolic cio-aconitase (ACO), and isocitrate dehydrogenase (IDH) were examined in navel oranges during fruit development. The results indicated that the sugar-acid ratio of fruits in different eco-regions changed significantly from 150 days after full bloom. The SPS and cytosolic ACO fruit activities had minor changes among different ecoregions throughout the experimental periods, whereas the activities of SS and IDH changed significantly in fruits among three eco-regions. Furthermore, the sugar-acid ratio and the activities of SS in the synthetic direction and IDH were the highest in south subtropics and the lowest in north mid-subtropics, probably due to the effects of climate conditions and/or other relevant eco-factors. It demonstrated that SS in the synthetic direction and IDH were of greater importance in regulating the sugar-acid ratio of navel oranges in different eco-regions, which provided new insights into the factors that determine the flavor quality of navel oranges and valuable data for guiding relevant agricultural practices. Index terms: navel orange, sugar-acid ratio, sucrose phosphate synthase, sucrose synthase, cytosolic aconitase, isocitrate dehydrogenase. ESTUDO SOBRE A RELAÇÃO AÇÚCAR-ÁCIDO E ATIVIDADES RELEVANTES METABOLIZADORAS DE ENZIMA EM FRUTOS DE LARANJA DE UMBIGO DE DIFERENTES ECOREGIÕESRESUMO -A qualidade do sabor das frutas cítricas é amplamente determinada pela relação açúcar-ácido, mas permanece incerto como enzimas metabolizadoras de açúcar e / ou do ácido regulam a relação açúcar-ácido de laranjas de umbigo e depois afetarem a qualidade dos frutos. No presente estudo, laranjas de umbigo Robertson (Citrus sinensis Osb.) foram coletadas de seis habitats representativos em três ecorregiões do Sichuan, na China. As mudanças na relação açúcar-ácido e as atividades da síntese de sacarose fosfato (SPS), síntese de sacarose (SS), aconitase citossólica (ACO) e isocitrato desidrogenase (IDH) foram examinadas em laranjas de umbigo durante o desenvolvimento dos frutos. Os resultados indicaram que a relação açúcar-ácido de frutas em diferentes ecorregiões alterou significativamente a partir de 150 dias após a plena floração. O SPS e as atividades ACO citossólicas das frutas tiveram pequenas alterações entre diferentes ecorregiões ao longo dos períodos experimentais, enquanto que as atividades da SS e IDH alteraram significativamente em frutas entre três ecorregiões. Além disso, a relação açúcar-ácido e as atividades da SS na direção sintética e IDH foram as mais elevadas em regiões s...

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