Anatomical and biochemical events during in vitro rooting of microcuttings from juvenile and mature phases of chestnut

Abstract

A comparative study of the in vitro rooting process of chestnut (Castanea sativa) shoots of the same genotype exhibiting juvenile (easy-to-root) and mature (difficult-to-root) characteristics is described. The two culture lines originated from shoots collected from the base (juvenile) and crown (mature) of an 80-year-old tree. Anatomically, juvenile and mature shoots had a similar stem structure at the time of excision, the main difference being that secondary phloem and xylem were more developed in mature than in juvenile shoots. A substantial reactivation of cell division was observed in both shoot lines 48 h after the root inductive treatment with indole-3-butyric acid. Meristemoids and root primordia developed only in juvenile shoots, beginning 3 d after the inductive treatment, and the first adventitious roots emerged 10 d after treatment. However, in mature shoots periclinal divisions of cambial cells occurred, especially on the phloem side, maintaining the normal orientation of the cambial derivatives. No meristemoids formed in this proliferating tissue. During the time course of the rooting process, more endogenous indole-3-acetic acid (IAA) was detected in mature than in juvenile shoots, indicating that the level of IAA is not the limiting factor accounting for the lack of rooting capacity in mature shoots. The levels of polyamines (putrescine, spermine and spermidine) were also higher in mature than in juvenile shoots.