NUCLEAR AND CYTOPLASMIC CHANGES ASSOCIATED WITH MATURATION IN THE VASCULAR CAMBIUM OF LARIX LARICINA

We studied the effects of apicaI maturation on the vascular cambium of juvenile and mature scions of Larix laricina (Du Roi) K. Koch that ha d been grafted on seedling rootstocks. Comparisons between the juvenil e and mature cambium in nuclear genome size, nuclear shape, DNA concen tration, number and volume of nucleoli per nucleus, and concentration of extranuclear RNAs, proteins and insoluble carbohydrates were conduc ted on four occasions during the annual cycle of cambial activity and dormancy. All investigated variables exhibited strong annual oscillati ons, whereas differences between the two maturation stages were less p rominent. Many of the differences between the two phases could be expl ained 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 low er genome size, lower DNA concentration, fewer nucleoli per nucleus an d a higher extranuclear concentration of insoluble carbohydrates than the juvenile cambium. The dormant mature cambium contained more extran uclear RNAs than the dormant juvenile cambium. The observed difference s provide circumstantial evidence of changes in chromatin organization or functioning, or both, during maturation.