As the auxin-ethylene interaction in climacteric fruit ripening has been highlighted, the hormonal regulation of aroma changes in climacteric fruits requires clarification. The influence of both phytohormones on the volatile organic compound (VOC) metabolism was evaluated during tomato (Solanum lycopersicum L.) fruit ripening. Tomato fruits cv. Micro-Tom and Sweet Grape at the mature green stage were randomly grouped according to treatment with ethylene (ETHY), auxin (IAA), or both (ETHY + IAA). At middle ripening, Micro-Tom ETHY + IAA fruits present VOC profiles similar to those of ETHY fruits, while Sweet Grape presents VOC profiles closer to those of IAA fruits. At full ripeness, Micro-Tom and Sweet Grape ETHY + IAA fruits show profiles closer to those of IAA fruits, suggesting that the auxin overlaps the ethylene effects. Aroma compounds positively correlated with consumer preferences (2-isobutylthiazole, 6-methyl-5-hepten-2-one, and others) are identified in both cultivars and have their contents affected by both hormone treatments. The transcription of genes related to the biosynthesis of important tomato VOCs that have fatty-acid and carotenoid precursors evidences their regulation by both plant hormones. Additionally, the results indicate that the observed effects on the VOC metabolism are not restricted to the Micro-Tom cultivar, as these are also observed in the Sweet Grape cultivar. In conclusion, ethylene and auxin directly regulate the metabolic pathways related to VOC formation, impacting tomato aroma formation during ripening since Micro-Tom fruits apparently at the same maturation stage have different aromas.
BONATO, V. C. B. Ethylene-auxin interaction and its influence on volatile profile during ripening of tomato (Solanum lycopersicum). 2015. 93p. Dissertação (Mestrado) -Faculdade de Ciências Farmacêuticas, Universidade de São Paulo, São Paulo, 2015.Fruit ripening is a complex and genetically programmed process through the fruit acquires characteristics (sweetness and acidity, color, softening, flavor and aroma, etc.) that make it attractive to consumers. The tomato fruit (Solanum lycopersicum) has been widely used as a model for studies on fruit ripening due to its nutritional and economic importance and advances in the understanding of its genetics and biochemistry. A set of 20 to 30 volatile substances, including alcohols, aldehydes, ketones and esters, which were derived from amino acids, fatty acids and carotenoids, contribute to the flavor. The hormone ethylene is closely related to the metabolic changes that occur in the maturation, including the generation of these volatile compounds, through the activation of transcription factors that regulate genes encoding proteins involved in this process. Although the knowledge about the biochemistry pathways that produces flavor compounds and the involvement of ethylene have advanced, little is known about the regulation of this process. In addition, ethylene is not the unique hormone that plays this role on fruit ripening. There is a growing body of evidence indicating the involvement of auxin in the maturation. The role of other hormonal classes is still little explored when compared to progress made on the role of ethylene in fruit ripening, especially regarding the regulation of the biosynthetic pathways of volatile compounds. This study aim to assess how the interaction between the indole-3-acetic acid (IAA), the most abundant auxin in plants, and ethylene influence the production of tomato fruit aroma. To do this, fruit from tomato cultivar Micro-Tom were treated with IAA and ethylene, separately and in combination. The results showed that the fruit groups characterized by having different profiles of volatile compounds. The treatment with IAA and IAA + ethylene caused delay in accumulation of volatile compounds derived from isoprenoid, as well as in the transcription of genes involved in the synthesis of these compounds: carotenoid cleavage dioxygenases 1A and 1B (SlCCD1A and SlCCD1B). The change from green to red and the accumulation of lycopene were also delayed in response to these two treatments. We also assessed the levels of transcripts of genes involved in the synthesis of volatile compounds derived from fatty acids (lipoxygenases [SlLOX], hydroperoxide lyases [SlHPL] and alcohol dehydrogenases [SlADH]), besides the levels of ethylene production, and IAA in free and conjugated form. The results were robust with respect to impacts on volatile compounds profiles, caused by the same hormone treatments in tomato variety Grape. The data suggest that auxin plays an important role in the synthesis of volatile compounds in tomato fruit, negatively regulating thi...
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