CONICET | Buscador de Institutos y Recursos Humanos

Tipburn in lettuce is a physiological disorder expressed as a necrosis in the margins of young developingleaves and is commonly observed under saline conditions. Tipburn is usually attributed to Ca2+deficiencies, and there has very limited research on other mechanisms that may contribute to tipburndevelopment. This work examines whether symptoms are mediated by increased reactive oxygen species(ROS) production.Two butter lettuce (Lactuca sativa L.) varieties, Sunstar (Su) and Pontina (Po), with contrasting tipburnsusceptibility were grown in hydroponics with low Ca2+ (0.5 mM), and with or without 50 mM NaCl.Tipburn symptoms were observed only in Su, and only in the saline treatment. Tipburn incidence inresponse to topical treatments with Ca2+ scavengers, Ca2+ transport inhibitors, and antioxidants wasassessed. All treatments were applied before symptom expression, and evaluated later, when symptomswere expected to occur. Superoxide presence in tissues was determined with nitro blue tetrazolium (NBT)and oxidative damage as malondialdehyde (MDA) content. Superoxide dismutase (SOD), catalase (CAT)and ascorbate peroxidase (APX) activities were assayed.Under control and saline conditions, tipburn could be induced in both varieties by topical treatmentswith a Ca2+ scavenger (EGTA) and Ca2+ transport inhibitors (verapamil, LaCl3) and reduced by supplyingCa2+ along with a ionophore (A 23187). Tipburn symptoms were associated with locally produced ROS.O2− and oxidative damage significantly increased in leaf margins before symptom expression, whiletopical antioxidant applications (Tiron, DPI) reduced symptoms in treated leaves, but not in the restof the plant. Antioxidant enzyme activity was higher in Po, and increased more in response to EGTAtreatments, and may contribute to mitigating oxidative damage and tipburn expression in this variety.

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