Nitric oxide and nitrite treatments reduce ethylene evolution from apple fruit disks

Abstract

'Golden Delicious' apple [Malus sylvestris var. domestica (Borkh.)] cortex disks suspended in solutions containing a nitric oxide (.NO) donor [S-nitrosoglutathione (GSNO) or sodium nitroprusside (SNP)], .NO gas, or nitrite (KNO2) were used to identify impacts of .NO on ethylene production and .NO2- on 'NO and ethylene production. Treatment with GSNO or SNP reduced ethylene biosynthesis compared with control treatments containing equimolar concentrations of oxidized glutathione (GSSG) or Na4(CN)6 respectively. Apple disk exposure to .NO gas did not impact ethylene production. Treatment with NO2- resulted in increased .NO production and decreased ethylene biosynthesis. Generation of .NO increased linearly whereas ethylene generation decreased exponentially with increasing NO2- treatment concentration. .NO was enhanced in autoclaved tissue disks treated with NO2-, suggesting that its production is produced at least in part by nonenzymatic means. Although this evidence shows .NO is readily generated in apple fruit disks by NO2- treatment, and ethylene synthesis is reduced by .NO/NO2- generated in solution, the exact nature of .NO generation from NO2- and ethylene synthesis modulation in apple fruit disks remains to be elucidated.