POLYAMINES AND ADVENTITIOUS ROOT-FORMATION IN THE JUVENILE AND MATURE PHASE OF ENGLISH IVY

The involvement of polyamines during adventitious root formation was evaluated using a de-bladed petiole rooting assay for the easy-to-root juvenile and difficult-to-root mature phase of English ivy (Hedera helix L.). Auxin (NAA 0.1 mM) stimulated root formation in juvenile phase cuttings, but failed to promote rooting in the mature phase. The addition of putrescine, spermine or spermidine (1.0 mM) with or without NAA (0.1 mM) did not affect the rooting response in either the juvenile or mature phase cuttings. There was a significant increase in endogenous levels of putrescine and spermidine in NAA-treated cuttings, but the only significant difference between the root forming juvenile and non-root forming mature phase cuttings was an increase in putrescine levels. In NAA-treated juvenile cuttings, the polyamine biosynthesis inhibitor DFMA (1.0 mM) promoted root formation from 9.2 to 14.5 roots per cutting, while DFMO (1.0 mM) reduced root formation from 9.1 to 1.4 roots per cutting. The promotion of rooting by DFMA was completely reversed by putrescine (1.0 mM), but putrescine, spermine or spermidine (1.0 mM) could not reverse the inhibitory effect of DFMO. Neither DFMA nor DFMO promoted root formation in mature phase cuttings. DFMA was also added to NAA-treated juvenile petioles at various stages during the root formation process. DFMA promoted rooting when applied during the early stages of root induction (0-3 d), but became inhibitory to root formation when applied during the organization (6-9 d) or root elongation stages (9-12 d).