Physiological and Molecular Mechanisms Governing the Postharvest Stress-Induced Accumulation of Antioxidant Phenolic Compounds in Carrots
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The use of postharvest abiotic stresses in fresh fruits and vegetables induces the accumulation of bioactive compounds. In the present study, the postharvest application of extreme conditions of wounding and hyperoxia stresses was evaluated as an approach to exploit the genetic potential of carrots to produce antioxidant phenolics compounds. Carrots responded to wounding and hyperoxia stresses accumulating hydroxycinnamic acids, mainly caffeoylquinic acids (CQAs) such as 3-O-caffeoylquinic acid (3-CQA), 3,5-dicaffeoylquinic acid (3,5-diCQA), and 4,5-dicaffeoylqinic acid (4,5-diCQA). Physiological and molecular studies were conducted to characterize further and understand the mechanisms governing the stress-induced accumulation of phenolics in carrots. A subtractive wound-induced cDNA library for carrots was generated to identify genes with potential involvement on the accumulation of phenolics that are up-regulated by wounding. Genes with putative function related with the production of stress signaling molecules were up-regulated by wounding stress in carrots. Likewise, genes related to primary and secondary metabolism were wound-induced. The role of reactive oxygen species (ROS), ethylene (ET) and jasmonic acid (JA) as signaling molecules that modulate wound response in carrots was characterized. Inhibitors of ROS biosynthesis, ET action, and JA biosynthesis alone and in combination were applied to shredded carrot tissue and the relative expression of genes with potential involvement on the biosynthesis of ROS, ET and JA were evaluated. Likewise, the relative expression of genes involved with primary and secondary metabolism was determined and phenolic compounds were quantified in the wounded-tissue treated with inhibitors. Results revealed that a complex cross-talk between ROS, ET, and JA, modulates the wound-response in carrots. Furthermore, it was demonstrated that ROS play the major role on the wound-induced activation of primary and secondary metabolism as well as on the accumulation of phenolic compounds in carrots. Likewise, ET and JA have an important role regulating ROS levels in the wounded-tissue. The information generated in this investigation allows for a greater understanding of the physiological and molecular mechanisms involved on the wound-response in carrot tissue. Likewise, it opens the possibility of potential strategies for the efficient use of carrots as biofactories of antioxidant phenolic compounds.
Jacobo Velazquez, Daniel A (2010). Physiological and Molecular Mechanisms Governing the Postharvest Stress-Induced Accumulation of Antioxidant Phenolic Compounds in Carrots. Doctoral dissertation, Texas A&M University. Available electronically from