IMPERMANENT INITIALS OF THE SHOOT APEX AND DIPLONTIC SELECTION IN A JUNIPER CHIMERA

Abstract

Shoot meristems of Juniperus davurica cv. Expansa Variegata possess an apical zonation pattern similar to that found in some angiosperms. Anticlinal divisions predominate in the outer layer, the tunica. The underlying core of cells, the corpus, has cell divisions oriented in all directions. Typically, this variety exists as a periclinal chimera, the outer layer genotypically albino and the inner core composed of normal, chlorophyll‐producing cells. In this condition a shoot appears green. Occasionally a tunica cell divides periclinally and displaces an initial in the apical region of the corpus. This event subsequently is expressed during ontogeny as an albino sector on the stem and leaves.Frequent variation in the width of an albino sector throughout ontogeny suggests a temporary nature of cells in the position of apical initials. A correlation was documented between the position of axillary bud release and a subsequent increase or decrease in the width of an albino sector. A model based upon stochastic processes and diplontic selection is proposed to account for the dynamic nature of chimeric patterns observed in this plant.