CYTOPHOTOMETRIC INVESTIGATION ON DNA AND NUCLEAR-PROTEIN AND THE PATTERN OF DNA METHYLATION IN EARLY ABSCISSION-AFFECTED FRUITS OF MALUS-DOMESTICA BORKH

Certain aspects of the chromatin of immature seeds were investigated i n embryo and endosperm tissue of control and shedding-affected fruits of Malus domestica Borkn. Changes in DNA and nuclear protein were anal yzed using the Feulgen and Fast Green (pH 8,1 and pH 2) methods. Cytop hotometric results did not show any significant differences in Feulgen and pH 8,1 Fast Green absorption among the samples. On the contrary, a considerable increase in pH 2 Fast Green absorption was observed in the seeds of shedding-affected fruit. It is assumed that this response is the consequence of a high content of histones, undetectable as a r esult of some postranslational modifications. An increase in the histo ne content in seeds of shedding-affected fruits might explain the grea ter compactness of the chromatin observed in this system. Differences in the chromatin structure between the two samples also emerged when t he cytological pattern of Ei-methylcytosine was taken into account: th e distribution of high-methylated regions, corresponding to certain he terochromatic portions of the genome, was differently localized in the nuclei of the different samples. These findings indicate that a numbe r of nuclear proteins and the DNA methylation status may be two compon ents, among others, of fruit degeneration and abscission in Malus dome stica.