JUVENILITY AND MATURATION IN CONIFERS - CURRENT CONCEPTS

Maturation in conifers includes several distinct and persistent change s in the growth habits of apical meristems. Despite many studies on ma turation in conifers, there are still many aspects of the process that have not been elucidated. For example, it is not known why maturation of cotyledon-derived tissue culture plantlets is rapid, whereas the n atural maturation process is gradual. Also, it is not known whether re juvenation occurs as a result of mature cells reverting to the juvenil e state, or whether rejuvenation results from selective multiplication of cells that have never matured. In this paper, I review the primary causes of maturation in woody plants, with emphasis on gene expressio n and its role in cell determination during the maturation process. Re cent experiments demonstrating both accelerated maturation and apparen t rejuvenation in several woody species are discussed with reference t o several maturation models.