Abstract
The success of vegetative propagation programmes strongly depends on adventitious rooting, a postembryonic developmental process whereby new roots can be induced from differentiated cells in positions where normally they do not arise. This auxin-dependent organogenesis has been studied at molecular, cellular, and developmental levels, and our knowledge of the process has improved in recent years. However, bioactive compounds that enhance adventitious root formation and possibly reduce undesirable auxinic side effects are still needed to ameliorate this process. From this point of view, our structure–activity relationship studies concerning urea derivatives revealed that some of them, more specifically, the N,N′-bis-(2,3-methylenedioxyphenyl)urea (2,3-MDPU), the N,N′-bis-(3,4-methylenedioxyphenyl)urea (3,4-MDPU), the 1,3-di(benzo[d]oxazol-5-yl)urea (5-BDPU), and the 1,3-di(benzo[d]oxazol-6-yl)urea (6-BDPU), constitute a category of adventitious rooting adjuvants. The results of our studies are presented here, in order either to highlight the positive effects of the supplementation of these urea derivatives, or to better understand the nature of their interaction with auxin.
Highlights
The innate static nature of plants is counterbalanced by their extraordinary ability to adapt their growth and development to the environment
This review reports the updated results regarding the effects of MDPUs and BDPUs on the adventitious rooting process
It has been demonstrated that MDPUs and BDPUs act as adventitious rooting adjuvant compounds in the simultaneous presence of auxin, the well-known plant growth regulator on which this organogenetic process depends
Summary
The innate static nature of plants is counterbalanced by their extraordinary ability to adapt their growth and development to the environment. Their adjuvant rooting activity was characterized by being (i) closely dependent on the symmetric nature, as the asymmetric corresponding molecules were ineffective; (ii) independent of the simultaneous exogenous supplementation of auxin, or responsible for a reduced concentration of an exogenously supplemented auxin, depending on whether the species is easy- or difficult-to-root; (iii) untied from callus formation, as a consequence of the totally absent, or at least reduced, exogenous auxin supplementation; (iv) the 5- and the 6-BDPU, a little less effective than the lead compounds We demonstrated that their considerably wide action spectrum includes herbaceous and woody Angiosperms as well as Gymnosperms, that their supplementation enhances adventitious rooting either in in vivo or in in vitro experimental conditions, and that this gives rise to a good-quality root system favoring the survival of rooted microcuttings [31]. We summarize the recent results obtained about the positive effects of the supplementation of these urea derivatives, alone or in the simultaneous presence of auxin (Table 1), and we explain the state of the art about the nature of their interaction with auxin, the real adventitious root inducer
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