ABSCISIC-ACID LEVELS AND CELL STRUCTURE IN SINGLE SEED TISSUES OF SHEDDING AFFECTED FRUITS OF MALUS-DOMESTICA BORKH

To improve knowledge of the processes involved in fruit abscission, the abscisic acid levels and the structure of both whole seed and single seed tissues were investigated in control (sample A) and shedding affected fruits (sample B) of Malus domestica. ABA content was measured in crude extracts by radioimmunoassay and the results were validated by physicochemical methods. Whole seeds were embedded and sectioned for light and electron microscopy studies. The ABA level in whole seeds was almost three times higher in the affected fruits than in the control. No difference in ABA content was observed between the embryos of the two samples, while in the endosperm, the nucellus and especially in the integuments, the A-BA level was clearly higher in sample B than in sample A. Delayed development and precocious cell differentiation as well as certain aspects of whole system degeneration were observed. The authors conclude that ABA levels seem to be one of the factors involved in fruit abscission in an early period of development.