Modulation of the Biosynthesis of Phenylpropanoids and Hydrolyzable Tannin Derivatives in Fruits through Long-distance Stresses
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The importance of secondary metabolites (SM) in plant defense mechanisms against environmental stresses as well as its benefits in human health have led to the study of how preharvest factors enhance their biosynthesis in fruits and vegetables. Pecans and strawberries have high level of bioactive phenolics including ellagitannins, gallotanins and proanthocyanidins. Wounding affects the production of SM as a local response, and as a systemic response in leaves, but this has never been tested in fruits. Organic agriculture claims that under this method of production, plants suffer more biotic stress and accumulate more SM in fruits. In this dissertation, the preharvest effects of biotic stress due to insect feeding and mechanical wounding were evaluated as modulators of phenolics in fruits. Wounding did not produce any differences in quality and vitamin C in fruits at harvest compared with the control. However, the level of total phenolics and soluble sugars in fruits from treated plants increased significantly 12% and 20% respectively. Moreover, increments in the level of specific phenylpropanoids were observed: epicatechin (160%), quercetin (190%) and rutin (190%), the ellagitannins/gallotanins derivatives ellagic acid (58% and gallic acid (130%). In addition, several genes related to phenolics biosynthesis and sugar metabolism were overexpressed. A hypothetical model is proposed to explain the modulation of phenolic compounds in fruits based on source/sink transport of sugars in favor of fruits from wounded leaves. In the following studies were used a generalist insect chewing in organic strawberry plants, and a specialist aphid feeding on pecan leaves. In strawberries no significant increments were detected for quality parameters, soluble sugars, phenolics, and related gene expression (except for the cell wall invertase gene). In pecan kernels, no differences were found in proanthocyanidins, gallotanins o ellagitannins derivatives levels due to the insect sucking the leaves. The results could explain how the wounding factor attributed to insect damages is connected to higher levels of phytochemicals in organic fruits. Furthermore, controlled mechanical wounding applied in leaves during preharvest could be used to increase phytochemicals in fruits.
Ibanez, Facundo (2015). Modulation of the Biosynthesis of Phenylpropanoids and Hydrolyzable Tannin Derivatives in Fruits through Long-distance Stresses. Doctoral dissertation, Texas A&M University. Available electronically from