Changes in the branching pattern of Pinus radiata derived from grafting are supported by variations in the hormonal content

Abstract

Maturation in woody species implies a lack in morphogenic competences, mainly the ability to root, which could be partially recovered by means of a reinvigoration method such as grafting. In this procedure, the cutting selected from the adult tree undergoes environmental changes in its architecture, passing from a complex symmetry to a longitudinal-growth system in which the effect of apical dominance is much more present. This work was focused on studying the effect of grafting procedures on the endogenous contents of several plant hormones, using for that purpose Pinus radiata terminal and axillary buds collected from trees with different states of reinvigoration. Results in terminal buds showed increasing amounts of indole-3-acetic acid (IAA) the more reinvigorated the plant material was, whereas an enhancement in total cytokinins (Cks) levels was observed in axillary buds. Abscisic acid (ABA) content decreased in axillary buds throughout reinvigoration, while in terminal buds a similar amount was found between non-reinvigorated trees and those which had been reinvigorated three times. The discussion is focused on the effect that IAA content in terminal buds exerts over other hormone content in axillary buds. Cks results in axillary buds corroborated previous findings in which the ratio of isopentenyladenine-type to zeatin (Z)-type Cks was reported as an ageing and vigour index. This index could be used to improve our knowledge about maturation and related processes from a hormonal point of view.