Cytohistological and cytochemical features of the seeds of Malus domestica Borkh, exposed to spring frosts

Malus domestica Borkh cv. Golden Delicious trees, exposed to spring frost, showed the occurrence of seeds with white (W), spotted (S) and black (B) integuments, with a different distribution, amount and damage in shedding and non-shedding fruits at several times after anthesis. While B seeds were completely degenerated, the S seeds showed hystological and cytochemical features that included a precocious embryo development stage, an embryonal cells shrinkage, an absence of reserves in the suspensor, endosperm and integuments, and a probable block of the routing of reserves, as a consequence of spring frost damages. All these features are the same occurring in seeds undergoing to natural abscission phenomenon and in theWseeds of shedding fruits observed in previous years. The S seeds damage is certainly attributable to meteorological events, because the S seeds were never found until the occurrence of the spring frosts. On the contrary, the damage in theWseeds, which do not show external symptoms in shedding fruits, may be due on the one hand to meteorological stress, and on the other hand to endogenous stress caused by natural abscission process. At 60 days post anthesis, at the end of fruit-set, the ripening fruits show a mean number of five well developedWseeds in normal cytohistological conditions. The data are discussed in relation to the general problem of natural abscission of immature fruits.