When stress and development go hand in hand: main hormonal controls of adventitious rooting in cuttings

Abstract

Adventitious rooting (AR) is a multifactorial response leading to new roots at the base of stem cuttings, and the establishment of a complete and autonomous plant. AR has two main phases: (a) induction, with a requirement for higher auxin concentration; (b) formation, inhibited by high auxin and in which anatomical changes take place. The first stages of this process in severed organs necessarily include wounding and water stress responses which may trigger hormonal changes that contribute to reprogram target cells that are competent to respond to rooting stimuli. At severance, the roles of jasmonate and abscisic acid are critical for wound response and perhaps sink strength establishment, although their negative roles on the cell cycle may inhibit root induction. Strigolactones may also inhibit AR. A reduced concentration of cytokinins in cuttings results from the separation of the root system, whose tips are a relevant source of these root induction inhibitors. The combined increased accumulation of basipetally transported auxins from the shoot apex at the cutting base is often sufficient for AR in easy-to-root species. The role of peroxidases and phenolic compounds in auxin catabolism may be critical at these early stages right after wounding. The events leading to AR strongly depend on mother plant nutritional status, both in terms of minerals and carbohydrates, as well as on sink establishment at cutting bases. Auxins play a central role in AR. Auxin transporters control auxin canalization to target cells. There, auxins act primarily through selective proteolysis and cell wall loosening, via their receptor proteins TIR1 (transport inhibitor response 1) and ABP1 (Auxin-Binding Protein 1). A complex microRNA circuitry is involved in the control of auxin response factors essential for gene expression in AR. After root establishment, new hormonal controls take place, with auxins being required at lower concentrations for root meristem maintenance and cytokinins needed for root tissue differentiation.

Exogenous auxin improves root morphology and restores growth of grafted cucumber seedlings

“…Meantime, the significantly higher number of root tips in auxin-treated plants (Table 1) indicates that the longest total root length of auxin-treated seedlings versus control was a consequence of a more branched root system, rather than longer individual roots. This finding fits well with the common presumption that auxin influences root morphology by inhibiting root elongation and increasing lateral root production (Overvoorde et al 2010;da Costa et al 2013;Kazan 2013). …”

“…The anatomical changes that occur during graft union formation include the death of cell layers at the graft interface, cohesion of the scion and rootstock (RS), proliferation of callus cells at the graft interface, and vascular differentiation across the graft interface to establish vascular continuity (Aloni et al 2008), while adventitious rooting (AR) in vegetative cuttings passes through two main phases: (a) induction, and (b) formation (da Costa et al 2013). There are several reports showing that both; graft union formation and AR formation are largely dependent on the presence and concentration of plant growth hormones (mostly auxin) (Ye 2002;Overvoorde et al 2010;Aloni 2013Aloni , 2014Diaz-Sala 2014).…”

“…There are several reports showing that both; graft union formation and AR formation are largely dependent on the presence and concentration of plant growth hormones (mostly auxin) (Ye 2002;Overvoorde et al 2010;Aloni 2013Aloni , 2014Diaz-Sala 2014). Auxin can also act when exogenously supplied, entering the stem via the cut surface of cuttings by inducing cell dedifferentiation, leading to a new root meristem later on (da Costa et al 2013). Because of that, the use of exogenously supplied auxin is a common practice of vegetative propagation of many ornamental plants, fruits and forest trees.…”

VEGETATIVE PROPAGATION Of VITEX DONIANA SWEET fROM ROOT SEGMENT CuTTINGS

“…The separation of these two phenomena allows leafy shoots to supply adventitious roots with carbohydrates. Carbohydrates contribute to the formation of adventitious roots by supplying energy and carbon necessary for cell divisions, establishment of the new root meristems and root formation itself (da Costa et al, 2013). The formation of adventitious roots is more important than the development of aerial shoots, as the later could fade after a few days or weeks, if there is no newly formed root to feed the leafy shoots.…”

The Use of Auxin Quantification for Understanding Clonal Tree Propagation

“…IAA concentrations are also similar between nodes of Corymbia torelliana × C. citriodora seedlings that differ in rooting capacity, and also between cuttings from C. torelliana × C. citriodora stock plants of different heights that differ in rooting capacity [110,129,171]. The rooting response of a tissue can be regulated by many factors other than auxins, including the sensitivity of cells to the auxin signal [165], the concentrations of rooting inhibitors in the base of cuttings [165], the levels of minerals and carbohydrates [172][173][174][175][176][177][178], and the degree of lignification or sclerification of the stem [33,110,179,180].…”