Changes in the Concentrations of Abscisic Acid in Fruits of Normal and Nr, rin and nor Mutant Tomatoes During Growth, Maturation and Senescence

Abstract

The concentrations of free and base-hydrolysable (bound) abscisic acid (ABA) were measured in fruits of cv. Rutgers (normal) and of the mutants Nr, rin and nor during growth, maturation and senescence. Measurements were made also of postharvest changes in free ABA in immature Rutgers fruits. Free ABA began to accumulate rapidly in the pericarp of developing fruits of Rutgers, Nr and rin during the period of most rapid growth but accumulation in nor was delayed and slower. Peak concentrations in Rutgers, Nr and rin were similar but the maximum level in nor was about 50% lower. Peak concentrations of free ABA coincided with the completion of growth in Rutgers and rin but peak levels in Nr and nor were not reached until several days later. Colouring in all strains occurred at approximately the same time as the accumulation of peak concentrations of free ABA. Changes in bound ABA paralleled those in free ABA in pericarp tissue of all strains but the levels were about one-seventh of those of free ABA. Free and bound ABA were measured in seeds and associated mucilaginous tissue only in 50% developed and fully grown fruits. In the younger fruits of Rutgers, Nr and rin, this fraction contained a higher concentration of free ABA than the pericarp tissue. In fully grown fruits, the level of ABA in the seeds and associated tissue was much less than in this fraction of younger fruits and less than half that in the pericarp tissue. Free ABA in seeds and associated tissues remained low in nor fruits of both ages. The ratios of bound and free ABA in seeds and associated tissues in all strains were generally similar to those found in pericarp tissue. In Rutgers fruits, free ABA increased after harvest. It is suggested that ABA is produced in both pericarp and seeds plus associated mucilaginous tissue. Accumulation of ABA does not seem to be a result of increased ethylene production but conversely may be involved in the increased ethylene evolution which accompanies ripening in normal strains. Since the pattern of changes in ABA and the accumulation of peak concentrations in pericarp tissue was not consistently related to growth but was closely related to the onset of symptoms of ripening or senescence, ABA may be a regulator of ripening in the tomato.