Diheteroarylurea derivatives as adventitious rooting adjuvants in mung bean shoots and M26 apple rootstock

Abstract

The present research investigates the biological profile of eight symmetrical diheteroarylureas and phenylheteroarylureas, testing their hypothetical cytokinin-like activity and rooting activity. Cytokinin-like activity was assayed by the betacyanin (so-called amaranthin) accumulation test and by the tomato regeneration test. The rooting activity was assessed using the mung bean rooting test, the apple stem slice test and the rooting of apple microcuttings. Three compounds, 1,3-di(pyrazin-2-yl)urea (3a), 1,3-di(benzo[d] oxazol-5-yl)urea (3b) and 1,3-di(benzo[d]oxazol-6-yl)urea (3c), enhanced adventitious root formation in apple stem slice test, but only 3b and 3c were active in the mung bean rooting test. Compound 3b, that showed the best rooting activity, was also able to enhance the adventitious root formation in apple microcuttings. None of the compounds showed cytokinin-like activity.

1,3-di(benzo[d]oxazol-5-yl)urea acts as either adventitious rooting adjuvant or xylogenesis enhancer in carob and pine microcuttings depending on the presence/absence of exogenous indole-3-butyric acid

“…The frequent lack of a good vascular connection between these ARs and the cutting vasculature has been recognised as the main problem of their malfunctioning, with negative consequences for cutting survival (Fleck et al 2009). The simultaneous presence of unusual chemicals, e.g., 5-BDPU or 6-BDPU, plus auxin, has been described to promote adventitious rooting, reducing the disadvantages of a treatment with auxin alone (Ricci et al 2006;Brunoni et al 2014). To enlarge the action spectrum of these urea derivatives to commercial and/or environmental important species, but also to extend the knowledge on their morphogenic roles, they were presently used in in vitro micropropagated cuttings of Ceratonia siliqua L. Indole-3-butyric acid, i.e., the endogenous precursor of IAA (Liu et al 2012, and references therein), is useful in many culture systems to improve AR formation when applied exogenously, alone or in combination of a little amount of cytokinin.…”

“…The final concentration of DMSO in the in vitro culture medium did not exceed the one considered toxic (0.2 %, v/v) (Schmitz and Skoog 1970). The 5-BDPU and the 6-BDPU, synthesized as previously reported (Ricci et al 2006), were of analytical grade. The aqueous solutions of benzylaminopurine (BAP), IBA and Kin were sterilized by filtration using 0.2-lm pore size sterile disposable filter units (Schleicher and Schuell).…”

“…Besides, a wide range of chemicals have been used in combination with auxin looking for higher rooting performance and reduction of deleterious effects of auxin treatment, i.e., formation of wide callus or emergence of stunted or malformed roots (Welander and Huntrieser 1981;Cheng et al 1992;Orlikowska 1992;Rugini et al 1993;Auderset et al 1997). N,N 0 -bis-(2,3-methylenedioxyphenyl)urea (2,3-MDPU), N,N 0 -bis-(3,4-methylenedioxyphenyl)urea (3,4-MDPU), and, more recently 1,3-di(benzo[d]oxazol-5-yl)urea (5-BDPU) and 1,3-di(benzo [d]oxazol-6-yl)urea (6-BDPU), all urea derivatives, are among these chemicals (Ricci et al 2003(Ricci et al , 2006(Ricci et al , 2008Brunoni et al 2014). In particular, based on structure-activity studies, Ricci et al (2003Ricci et al ( , 2008 reported that 2,3-MDPU and 3,4-MDPU enhance AR formation in Malus pumila Mill.…”

“…M26 stem slices and in Pinus radiata D. Don stem cuttings, in the presence of exogenous auxin. 5-BDPU and 6-BDPU also exert an endogenous and/ or exogenous auxin-adjuvant effect on AR formation in distantly related plants and systems, i.e., mung bean shoots, apple stem slices, Arabidopsis seedlings and Pinus radiata hypocotyl cuttings, even if they have no auxin-or cytokinin-like activity (Ricci et al 2006;Brunoni et al 2014).…”

“…As large-scale vegetative propagation depends on the rooting ability of micropropagated shoots, a research was carried out to improve not only the in vitro rooting phase, but also the following ex vitro acclimatisation phase of carob difficult-to-root micropropagated cuttings by the use of 5-BDPU or 6-BDPU, because important adventitious rooting adjuvant compounds (Ricci et al 2006;Brunoni et al 2014). This research is the first attempt to utilise these compounds to enhance adventitious rooting in this valuable woody angiosperm, and to compare histologically results with those obtained from the cuttings of Pinus radiata, a distantly-related woody gymnosperm, for which both compounds are AR-effective (Brunoni et al 2014).…”