Arsenic compounds generate diverse effects in all living organisms. In citrus (Citrus L. sp.), they reduce acidity and improve fruit quality by unknown mechanisms. The major organic acid in citrus fruit is citric acid, which begins accumulating early in fruit development, reaches a peak in middle-sized fruit and then, in most species, declines as the fruit matures. In an attempt to understand the basis of the effect of arsenite, it was applied to `Minneola' tangelo (Citrus paradisi Macf. × C. reticulata Blanco) ≈6 weeks postanthesis, and a detailed analysis of total titratable acidity and citric acid concentration was performed throughout fruit growth. Within 35 days after arsenite application, total acid content and citrate concentration were slightly lower compared with the controls, and this difference persisted throughout fruit development. The concentrations of other organic acids were not reduced by the treatment. Sodium arsenite reduced the citrate concentration in `Eurieka' lemon callus [Citrus limon (L.) Burm.] also, without affecting tissue growth. Extractable activity of citrate synthase in treated fruit was inhibited within 1 day following arsenite spray, but recovered to a normal level a few days later. In contrast, gene expression was remarkably induced 1 day following treatment, which might explain the recovery in enzyme activity. Data suggest that reduction in acid accumulation may not be related to the initial inhibition of citrate synthase activity.
Arsenite Reduces Acid Content in Citrus Fruit, Inhibits Activity of Citrate Synthase but Induces Its Gene Expression
