Polyamines and ethylene in relation to adventitious root formation in Prunus avium shoot cultures

Abstract

An attempt was made to identify some of the hormonal factors that control adventitious root formation in our Prunus avium micropropagation system in order to improve rooting in difficult‐to‐root genotypes. Changes in endogenous contents of free polyamines were determined at intervals during auxin‐induced rooting of shoot cultures. Accumulation of putrescine and spermidine peaked between days 9 and 11. Spermine was only present in traces, Exogenously supplied putrescine or spermine (50‐500 μM), in the presence of optimal or suboptimal levels of indolebutyric acid (IBA), had no effect on rooting percentage or root density, except for spermine at 500 μM. At this external concentration spermine caused a substantial accumulation in both free spermine and putrescine. The use of several inhibitors of polyamine biosynthesis, namely α‐difluoromethylornithine (DFMO), α‐difluoromethylarginine (DFMA), dicyclohexylammonium sulphate (DCHA) and methylglyoxal‐bis‐guanyl‐hydrazone (MGBG) alone or in combination in the 0.1 to 5 μM range, resulted in an inhibition of rooting that was partially reversed by the addition of the corresponding polyamine. Cellular polyamine levels were significantly reduced by DFMO and DFMA but not by DCHA and MGBG, Labeled putrescine incorporation into spermidine increased somewhat in the presence of the ethylene synthesis inhibitor aminoethoxyvinylglycine (AVG). A system based on [3,4‐14C]methionine incorporation was used to measure ethylene synthesis by the in vitro cultured shoots. Label incorporation was drastically reduced by 10 μM AVG and increased 3.5‐fold in the presence of 50 μM IBA with respect to controls (no IBA). Labeled methionine incorporation into spermidine increased to some extent when ethylene synthesis was inhibited by AVG. Adding the ethylene precursor 1‐aminocyclopropane‐l‐carboxylic acid (ACC) to the rooting medium significantly inhibited rooting percentage; AVG caused the formation of a greater number of roots per shoot but delayed their growth. Supplying the shoots with both compounds resulted in an intermediate rooting response, in which both rooting percentage and root density were affected. These results indicate that polyamines may play a significant role at least in some stages of root formation. The polyamine and ethylene biosynthetic pathways seem to be competitive but under our conditions, the enhancement of one pathway when the other was inhibited, was not dramatic. Although IBA promoted ethylene synthesis, AVG, which drastically reduced it, also promoted root formation. Thus, the auxin effect on root induction cannot be directly related to its ability to enhance ethylene synthesis.

Acclimation to soil flooding — sensing and signal-transduction

“…For instance, ethylene inhibited adventitious root formation in pea (Pisum sativum) cuttings (Nordström and Eliasson, 1984) and Prunus avium explants (Biondi et al, 1990), whereas it stimulated root initiation in cuttings of Picea abies (Bollmark and Eliasson, 1990). Also, experimental conditions seem to matter, as contrasting results were found in various studies on mung bean (Vigna radiata -e.g., Robbins et al, 1983 vs. Geneve andHeuser, 1983).…”

Peroxidase and polyamine activity variation during thein vitrorooting ofBerberis buxifolia

“…However, other compounds could also be used as rooting markers, and polyamines have been the most studied in recent times (Baraldi et al 1995;Hausman et al 1995;Heloir et al 1996;Gaspar et al 1997). Thus, a positive relationship between polyamine accumulation and the initial stages of adventitious root formation has been reported in many systems (Friedman et al 1982(Friedman et al , 1985Tiburcio et al 1989;Torrigiani et al 1989;Biondi et al 1990;Altamura 1994). Although the involvement of polyamines in root formation is generally accepted, the specific role they play in this process remains to be elucidated and information about the exact rooting phase in which they are involved is very scarce.…”

The Physiology of Adventitious Roots

“…For example, in tobacco (Nicotiana tabacum; McDonald and Visser, 2003), sunflower (Liu et al, 1990), and Prunus avium (Biondi et al, 1990), ethylene treatments reduced adventitious rooting. By contrast, the ethylene precursor 1-aminocyclopropane-1-carboxylic acid enhanced adventitious rooting in stem cuttings of grape (Riov and Yang, 1989) and Norway spruce (Picea abies; Bollmark and Eliasson, 1990), whereas ethylene appeared to have no effect on adventitious rooting in apple (Harbage and Stimart, 1996).…”