HISTOLOGICAL AND CYTOCHEMICAL ASPECTS OF FLOWER BUD FORMATION IN APPLE

Preceding the appearance of morphologically distinguishable flower primordia a distinct change takes place in the zonation of the apex within the bud. Following an increase in mitotic activity all over the apex the position of the central meristem is directly below the middle part of the subdermatogen. This conversion of the histological structure results in the disappearance of the middle part of the accessory tunica layer.

Before this histological differentiation, i.e. in apices still with vegetative structure, there are some cytochemical dissimilarities between apices induced and inhibited for flower initiation. Apices in buds under flower inductive conditions possess a higher relative level of DNA in the cell nuclei of the central meristem and apical axial zone, compared with apices in which flower initiation is inhibited.

Apices of buds from trees sprayed with ethephon to promote flowering showed similar, though less marked, changes in the pattern of DNA levels.