Nuclear and cytoplasmic changes associated with maturation in the vascular cambium of Larix laricina.

We studied the effects of apical maturation on the vascular cambium of juvenile and mature scions of Larix laricina (Du Roi) K. Koch that had been grafted on seedling rootstocks. Comparisons between the juvenile and mature cambium in nuclear genome size, nuclear shape, DNA concentration, number and volume of nucleoli per nucleus, and concentration of extranuclear RNAs, proteins and insoluble carbohydrates were conducted on four occasions during the annual cycle of cambial activity and dormancy. All investigated variables exhibited strong annual oscillations, whereas differences between the two maturation stages were less prominent. Many of the differences between the two phases could be explained by delayed spring reactivation and accelerated onset of dormancy in the mature cambium compared with the juvenile cambium. At the time of reactivation and during activity, the mature cambium exhibited lower genome size, lower DNA concentration, fewer nucleoli per nucleus and a higher extranuclear concentration of insoluble carbohydrates than the juvenile cambium. The dormant mature cambium contained more extranuclear RNAs than the dormant juvenile cambium. The observed differences provide circumstantial evidence of changes in chromatin organization or functioning, or both, during maturation.