Age-related changes in the hormonal status of Pinus radiata needle fascicle meristems

Distinct developmental states in woody trees are associated with different types of plant hormones disclosing a variety of roles throughout ageing and maturation. The plant hormones abscisic and indole-3-acetic acids (ABA and IAA, respectively) as well as several cytokinins (Cks) were analysed to ascertain the effect of maturation processes over the hormonal status in the needle fascicle meristem of Pinus radiata. As plant material, needles from three different ages collected from trees with two different states of reinvigoration, one- and three-time-grafted material, were used. Once-reinvigorated material showed decreasing amounts of ABA, IAA and Cks throughout the needles maturation and ageing. Three-time-reinvigorated material presented the lowest levels of IAA and Cks in the oldest needle fascicle meristems. ABA content was similar in the current-year growth and the latest-year needle fascicle meristems, but a slight increase was obtained in the intermediate developmental state. The ratio of isopentenyladenine-type to zeatin-type Cks, reported as an index of ageing and vigour in previous studies, was ratified in the current work. Results might describe the role of several hormones during ageing and maturation processes, as well as might establish the importance of the different forms of Cks not only during tree ageing, but also throughout organ maturation. Our findings demonstrate that not all cytokinin forms are equally present in the regulation of maturation and ageing. (C) 2004 Elsevier Ireland Ltd. All rights reserved.