Study on the free-radical production and stress signal transduction of jasmonates and abscissic acid

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Drought stress was applied to ‘Shiranui' trees [(Citrus unshiu Marc.? Citrus unshiu Osbeck)? Citrus reticulata Blanco], and xanthoxin, abscisic acid (ABA), phaseic acid (PA), dihydrophaseic acid (DPA), epi-dihydrophaseic acid (epi-DPA), and jasmonates were monitored in fruit and leaf. They were quantified using the respective deuterium-labeled internal standards. Xanthoxin, ABA, and DPA concentrations in the pulp of the drought-stressed trees were found to be higher than those of the well-watered trees throughout development. Xanthoxin concentrations, however, were lower than those of ABA. These results may imply a rapid turnover from xanthoxin to ABA. In addition, ABA concentrations in the leaf were higher in drought-stressed trees than the well-watered trees, although PA and DPA levels between the drought-stressed and well-watered trees were not clear. DPA was found to be the primary metabolite in the pulp, skin, and leaf. Both jasmonic acid (JA) and ABA concentrations in the pulp, skin, and leaf showed high values in the drought-stressed trees. However, JA levels in the pulp decreased as the harvest approached. Sucrose concentrations in the pulp of the drought-stressed trees were higher than those of the well-watered trees. ABA and jasmonate applications induced stomatal closure in leaf. The effect of ABA on stomatal closure was stronger than that of jasmonate.Antioxidant activities and antioxidants of some tropical fruits were investigated. Total phenolics and ascorbic acid were analyzed as antioxidants. IC 50 values of superoxide and 1-diphenyl-2-picrylhydrazyl (DPPH)-radical scavenging activity in fruit are generally linked with total phenolics. n-Propyl dihydrojasmonate (PDJ) treatment decreased chilling injury. In general, IC 50 values of superoxide and DPPH radical scavenging activity were also associated with the degree of chilling injury. These results suggest the connections among jasmonates, ascorbic acid, and polyphenolics.