Nuclear size and shape changes in fusiform cambial cells of Abies balsamea during the annual cycle of activity and dormancy

Abstract

Interphase, prophase, and telophase nuclei were measured at different times during the year in fusiform cambial cells located at the base of the main stem of 6-year-old trees and in 1-year-old shoots from the top of 21-year-old trees. In both materials, the size and shape of nuclei exhibited seasonal changes that were independent of the cell cycle. Nuclear length was greater, whereas nuclear width and depth were smaller, when the cambium was dormant than when it was active. Nuclear volume gradually declined during the growing period and increased during the rest stage of dormancy. Nuclei had the highest surface to volume ratio in the quiescence stage of dormancy. During cambial activity, the projected area of prophase nuclei decreased, whereas it did not change for telophase nuclei. Nuclear volumes from the present investigation were combined with nuclear DNA contents previously recorded to estimate seasonal changes in nuclear DNA concentration which appear to be associated with the annual cycle of cambial activity and dormancy. Key words: balsam fir, periodicity, nucleus, xylogenesis, rest.