Characterization of Muskmelon Fruit Peroxidases at Different Developmental Stages

An increase in exocarp peroxidase activity was observed in fruit at 5 to 30 days post pollination (DPP), and decreased at 40 and 50 DPP. Total peroxidase activity of the mesocarp was significantly lower than the exocarp in all developmental stages. Mesocarp peroxidase activity decreased consecutively from outer, to middle and, to inner tissue at every developmental stage. Total activity in the mesocarp peaked at 20 DPP. Native-PAGE of exocarp tissue showed at least two cathodic (basic) peroxidases and two anionic (acidic) peroxidases. The number of isozymes was greatest and bands most intense at 30 DPP. IEF-PAGE of the 5 to 50 DPP fruit exocarp showed at least 8 peroxidase isozymes (pI 4.6 to 9.6). Anion exchange chromatography showed only one peak of anionic peroxidase activity that was not evident until 15 DPP. This peak was greatest at 30 DPP and declined at 40 and 50 DPP. Cationic peroxidase isozymes appeared to be the predominant and most intense isoforms throughout fruit development. The changes in peroxidase activity corresponded to fruit formation and may be associated with susceptibility to fruit rot.