Evolution of polygalacturonase and pectin methyl esterase activity during the storage of dudaim melons harvested at two maturity stages

Authors: HATAMI, MOHSEN - University Of Tehran; SOLTANI, FOROUZANDEH - University Of Tehran; KALANTARI, SIAMAK - University Of Tehran; Beaulieu, John

Submitted to: Italus Hortus
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/9/2021
Publication Date: 9/17/2021
Citation: Hatami, M., Soltani, F., Kalantari, S., Beaulieu, J.C. 2021. Evolution of polygalacturonase and pectin methyl esterase activity during the storage of dudaim melons harvested at two maturity stages. Italus Hortus. 28(2):58-69. https://doi.org/10.26353/j.itahort/2021.2.5869.
DOI: https://doi.org/10.26353/j.itahort/2021.2.5869

Interpretive Summary: The dudaim (also known as the Queen Anne’s pocket melon) is a specialty melon grown in Iran for their high fragrance, ornamental beauty and antidotal medicinal properties. Due to the strong pleasant aroma, some cultivars of dudaim are used for cosmetic purposes in Iran. Some people store dudaim melons in wheat straw and use its pleasant smell in their homes and cars. In Iran dudaim fruit is generally harvested in the ripe stage at optimum “maturity” and they are not stored. Most fruit are generally harvested about one month after flowering, as the plant tendrils begin to desiccate. However, melon fruit harvested at full maturity may have a short storage life, which is associated with the disintegration of cell walls that causes changes in fruit firmness. On the other hand, fruit used for aromatic and ornamental usages are often harvested early, stored and then utilized. To slow or to halt this quality decline, fruit are either stored under refrigeration or room storage, or processed. Decreasing the storage temperature slows the metabolic activity in the stored product, as well as prolonging fruit quality, including firmness retention and aromatic qualities. Yet, we recently demonstrated that some cultivars of dudaim melon exhibit chilling injury, and therefore, 21 days after anthesis (DAA) harvest and storage at a non-chilling temperature, such as 13 °C, provided better storage conditions for these dudaim fruit. Softening is a universal feature in the ripening and/or senescence of fleshy fruits and is typically accompanied by degradation of the middle lamella and loss of cell due to solubilization of cell wall pectin. Generally, the pectolytic enzymes involved in softening that have been studied in melons are polygalacturonases (PG) and pectin methyl esterase (PME). However, the effects of maturity stage and postharvest storage (time × temperature) on the activities of these two cell wall enzymes has not been elucidated in dudam melon. Also, we found no literature attempting to associate these enzymes with fruit ripening and softening of dudaim fruit. In this report, we present the PG and PME changes of two maturity stages (21 and 28 days after anthesis, DAA) in three cultivars (‘Zangi-Abad’, ‘Kangavar’ and ‘Kermanshah’) of dudaim melon during three weeks of storage at two (5 °C and 13 °C) temperatures.

Technical Abstract: To investigate the polygalacturonase (PG) and pectin methyl esterase (PME) activity changes of dudaim melon (Cucumis melo Group Dudaim), three cultivars including ‘Zangi-Abad’, ‘Kermanshah’ and ‘Kangavar’ were planted. Female flowers were then tagged at anthesis, and fruit were harvested at two stages of maturity including 21 and 28 d after anthesis (DAA). Harvested fruit were stored at 5 or 13 °C for three weeks and firmness, ethylene production, activity of PG and PME were evaluated during storage. In all three cultivars at most times during storage, PME activity of early-harvested fruit (21 DAA) was greater than late-harvested fruit (28 DAA). Contrarily, the late-harvested fruit did not have significant fluctuations during storage. In early-harvested fruit the trend of PME changes was further downward and in some treatments (e.g., early-harvested ‘Zangi-Abad’ fruit stored at 13 °C) increased. The general trend of changes in PG activity in early-harvested fruit was increased up to day 14 (in ‘Zangi-Abad’ and ‘Kermanshah’) and day 7 (in ‘Kangavar’) and then decreased until the end of storage. ‘Kangavar’ fruit behaved differently compared to the other two cultivars in terms of the two enzymes measured. Comparison of firmness and enzymes levels established a relationship between PG and PME activities and fruit firmness in dudaim melon. Based on the results of this study, the activity of the two enzymes measured in dudaim fruit varies depending on the time of fruit harvest (i.e., number of days after anthesis), storage temperature and storage duration.