Stimulation of putrescine biosynthesis via the ornithine decarboxylase pathway by gibberellic acid in the in vitro rooting of globe artichoke (Cynara scolymus)
2001
Le Guen-Le Saos, F. | Hourmant, A.
Rooting and growth of globe artichoke (Cynara scolymus) cuttings were improved by supplementing the rooting medium with 10 micromolar gibberellic acid (GA3). Exogenous putrescine (Put) (0.5 mM) raised the percentage of rooting to the same level as GA3, but decreased the number of roots per plant. Addition of Put to GA3 produced the same effects on growth parameters and rooting percentage as Put alone. Changes in endogenous contents of free polyamines (PAs) were determined in plants cultured 4 weeks in a rooting medium. Whatever the treatments, rooting caused a large decrease in Put, the largely predominant PA, in the leaves. GA3 increased the free Put content of the leaves and roots. DL-alpha-difluoromethylarginine (DFMA), which inhibits arginine decarboxylase (ADC), did not affect rooting while Put content was decreased by 12-15%. DFMA changed neither GA3 effects nor those from DFMO when used in combination. An inhibitor of ornithine decarboxylase (ODC), DL-alpha-difluoromethylornithine (DFMO), inhibited leaf growth as well as rooting and decreased the Put content; these effects were partially reversed by addition of Put. GA3 combined with DFMO did not alleviate the inhibitory effects of DFMO. The GA3 treatment caused a clear stimulation of ODC activity in the leaves; it also stimulated 14C-putrescine uptake (2.8-fold) by leaves and its translocation towards roots. These results indicate that the ODC pathway mediates the hormone-induced rooting response in globe artichoke. Moreover, a release of Put from its conjugates could contribute to the increase of free-Put levels in the roots under GA3 treatment. Thus, Put can be considered to be a good marker of rhizogenesis.
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