Cell wall‐degrading enzymes and pectin solubility and depolymerization in immature and ripe watermelon (Citrullus lanatus) fruit in response to exogenous ethylene

Abstract

Watermelon fruit have been shown to be extremely sensitive to exogenous ethylene, exhibiting acute symptoms of whole‐fruit softening and placental‐tissue water‐soaking following short periods of exposure to the gas. This study addressed the firmness, specific activities of cell wall hydrolases, and solubility and molecular mass properties of polyuronides in placental tissue in response to treatment of intact fruit with ethylene. Watermelon fruit were harvested at the immature and full‐ripe stages and exposed to 50 µl l−1 ethylene for 6 days at 20°C. The firmness of placental tissue from ethylene‐treated ripe and immature fruit decreased nearly 80% during 6 days of ethylene exposure, whereas the firmness of placental tissue from fruit maintained in air remained relatively constant up to day 3 and then decreased slightly (12%) during the following 3 days of storage. Although ethylene treatment in some cases influenced the levels of extractable placental‐tissue polygalacturonase (EC 3.2.1.15), pectinmethylesterase (EC 3.2.1.11), and α‐(EC 3.2.1.22) and β‐galactosidase (EC 3.2.1.23) specific activities, these effects were not observed for fruit of both developmental stages and appeared not to be directly involved in the water–soaking syndrome. Symptoms of water‐soaking were accompanied by increases in the levels of water‐ and CDTA (trans‐1,2‐cyclohexanediamine‐N,N,N',N′‐tetraacetic acid)‐soluble polyuronides and significant molecular mass downshifts in polyuronides in both immature and ripe watermelon fruit. Polyuronide depolymerization in ethylene‐treated ripe fruit was extensive. The parallel trends of enzyme changes in ethylene‐ compared with air‐treated fruit indicate that extractable enzyme levels are not associated with development of the water‐soaking disorder. The potential involvement of membrane dysfunction in the water‐soaking phenomenon is discussed.

Modification of Cell Wall Polysaccharides during Drying Process Affects Texture Properties of Apple Chips

“…Plant cell wall and the middle lamella are known to control the way in which plant tissues undergo mechanical deformation and failure during mastication [7,8]. The plant cell wall is made up of complex polysaccharides, phenolic compounds, and proteins stabilized by covalent and noncovalent (e.g., ionic) linkages.…”

Isolation and expression analysis of ethylene receptor genes from melon(Cucumis melo) fruit

“…The expressions of ethylene receptors associate with the function and thus the capacity of the plant tissue to respond to ethylene. The fruit of the cucurbitaceae family such as melon and watermelon also develop watersoaking, a physiological disorder upon ethylene exposure (Karakurt and Huber, 2002;Ergun et al, 2005). The application of ethylene to melon fruit cv ananas resulted in the development of the watersoaking disorder after 9 days of storage.…”

“…In climacteric fruit species, ethylene is effective in many physiological events during postharvest ripening. It directly affects factors influencing the shelf life of a fruit including softening, wooliness, watersoaking, and related deteriorations (Karakurt and Huber, 2002;Karakurt and Huber, 2004;Mao et al, 2004;Lima et al, 2005). Ethylene influences fruit ripening through involvement in chlorophyll degradation, increasing respiration rate, carotenoid synthesis, autocatalytic ethylene production, and the expression of genes that leads to the enhancement in the activities of enzymes responsible for starch to sugar conversion and cell wall degradation (Theologis, 1993;Wilkinson et al, 1997).…”

The molecular characterization and expression analyses of ethylene receptor genes from watermelon fruit

“…Fruits were harvested at the commercial ripening stage Huber, 2002, 2004) and immediately transported to the laboratory at the Faculty of Agriculture, Süleyman Demirel University, Isparta, Turkey. Fruits were surfacesterilized and treated with 50 µL/L ethylene for 24 hours at 20 °C as previously described (Karakurt and Huber, 2002). Samples were taken from the placental tissue and frozen in liquid nitrogen.…”

“…The fruits were harvested at commercial ripening stage (Karakurt and Huber, 2002) and stored at 20 °C for 10 days. Fruit samples were removed 4, 8, and 12 h and 1, 2, 4, 6, 8, and 10 days after storage.…”