Amitosis and endocytogenesis in the fruit of Malus sylvestris | Amitosis and endocytogenesis in the fruit of Malus sylvestris [Apple, non-pathogenic physiological 'cork spot' necrosis]

Cyto-histological investigations on the initiation and development of a non-pathogenic physiological ‘cork spot’ necrosis in the outer cortex of the fruit of Malus sylvestris Mill. ‘York Imperial’ revealed two distinct aberrancies, namely, amitotic nuclear division and intracellular or endogenous proliferations without hyperplasia per se The incipient necrotic condition becomes evident internally about 3 weeks after fruit set as minute isolated, discoloured, amorphous spots of disorganized ruptured cells within otherwise healthy cortical tissue The disorganization continues slowly with adjoining cells becoming similarly necrotic After the lysis of the initial cork spot cells, about 1 month later, sporadic cellular changes occur in various healthy vacuolated cortical cells contiguous to and encompassing the necrotic tissues. The nuclei increase in size and volume as they assume distinctive positions in preparation for amitotic nuclear divisions. The enlarged nucleus or macronucleus, containing one or several nucleoli, divides by a distinct cleavage developing from a constriction perpendicular to its longitudinal axis The division results in the amitotic formation of two daughter micronuclei that usually become separated by the formation of a cell wall. No evidence of cell plate formation was observed and the method of cell wall formation could not be determined. Repeated amitotic divisions of the micronuclei result in an intracellular or endocytogenetic proliferation of parenchymatous cells that are invariably confined within the original mother cell until its wall ruptures The endogenous proliferations are released into lacunae or intercellular spaces, eventually become disorganized, and disintegrate, with the accumulated residual increments resulting in an overall ‘cork spot’ appearance.