DEVELOPMENTAL STAGES AND GIBBERELLIN ACTIVITY IN OVULES OF ABSCISSION-AFFECTED FRUITS OF MALUS-DOMESTICA BORKH

Apple fruits were collected in the period between 20 and 49 days after anthesis. The relation between histological structure and gibberellin content was investigated in ovules of control fruits (sample A), fruit-drop affected fruits not yet abscinded from the plant (sample B) and fruit-drop affected fruits already abscinded from the plant (sample C). The results of the histological analyses showed that: i) ovules from sample A generally contained a developing embryo, a dividing endosperm, and a conspicuous antipodal tissue; ii) ovules from sample B were degenerating. However, they contained a degraded embryo mainly in fruits collected 29 days post anthesis. No endosperm or antipodal cells were detected; iii) ovules from samples C also degenerated and had no recognizable structure. Gibberellins were determined in ovules isolated from the same three samples of fruits. The gibberellin content was very low in all samples and quantitative differences between sample A, on the one hand, and samples B and C, on the other, were only detectable 49 days after anthesis. Moreover, biological activity appeared to be distributed in different Rf-zones in the TL chromatogram, suggesting the presence of various gibberellin-like substances. The differences observed were confirmed after HPLC purification. Further analyses by means of GC and GC-MS led to the identification of GA4 and GA63 as two of the GAs present in ovules from sample A. The results obtained are discussed in relation to fruit abscission heterogeneity.