Enhanced ethylene evolution and electrolyte leakage from methomyl-treated cotton ( Gossypium hirsutum)

Abstract

Cotton, Gossypium hirsutum L., may undergo premature defoliation following treatment with methomyl, S-methyl-N-[(methyl-carbamoyl)oxy]-thioacetimidate, an insecticide used to control Heliothis spp. (cotton bollworm and tobacco budworm). The literature suggests that cotton defoliation is associated with both enhanced ethylene evolution and incresed membrane permeability. This study was initiated to evaluate ethylene evolution patterns and membrane permeability of cotton leaves grown under field and laboratory conditions following methomyl treatment. Ethylene evolution and electrolyte leakage (used as an indicator of increased membrane permeability) were monitored in leaf discs collected from cotton plants previously treated with 0.14, 0.28 and 0.56 kg ha −1 methomyl. Ethylene evolution was significantly increased in leaf discs within 9 h after one methomyl application. Further experiments indicated increased ethylene evolution up to 3 days after treatment. Increases in electrolyte leakage from leaf discs were detected in discs collected 24 h after methomyl treatment and incubated for 12 h in 0.2 M mannitol. Electrolyte leakage remained higher in treated tissue up to 6 days following methomyl treatment. Ethylene evolution was stimulated prior to electrolyte leakage in the experiments in which both were measured, suggesting that increased electrolyte leakage from methomyl-treated tissue occurred as a result of alterations in membrane permeability associated with enhanced ethylene production.