Involvement of polyamines in the adventitious rooting of micropropagated shoots of the apple rootstock MM106

Abstract

Apple rootstock MM106 shoots, raised in vitro, rooted at 96.7% after culture on a medium supplemented with an auxin for 5 d in darkness followed by culture on a second medium without growth regulators for 25 d in light. In control conditions (in absence of auxin in the first medium), these shoots did not root. Putrescine (PUT), spermidine (SPD), cyclohexylamine (CHA), and aminoguanidine (AG) enhanced rooting when applied during the first d of culture in the absence of IBA; on the contrary, α-difluoromethylornithine (DFMO) added to the first medium with IBA inhibited rooting. The endogenous levels of indole 3-acetic acid (IAA) and indole 3-acetylaspartic acid (IAAsp) increased up to a maximum concentration at days 2 and 3, respectively, in initial rooting conditions. PUT, when added with IBA, did not affect the typical IAA and IAAsp increase; when applied alone, it provoked an increase of their levels. Similar results were recorded with CHA. SPD, AG, and DFMO did not induce an increase of IAA and IAAsp in nonrooting conditions. The levels of endogenous PUT increased to a maximum at day 2 in rooting conditions; it was slightly affected by exogenous PUT and CHA application but reduced by SPD, AG, and DFMO. In rooting conditions, if the first medium was supplemented with SPD or AG, a small increase in peroxidase activity was observed, similar to that obtained with PUT treatment. The present work indicates an involvement of polyamines in the control of rooting and an interaction with auxins during the physiological phase of rooting. The consequence of this relationship was a different rooting expression, according especially to the content of these regulators in the culture medium.

ROOTING SHOOTS OF APPLE VARIETIES AND THEIR TETRAPLOIDS OBTAINED BY THE in vitro TECHNIQUE

“…Similar polyamine effect on root formation of apple rootstock microcuttings was reported by Naija et al [2009]. In turn, the high positive correlation between in vitro rooting and the increased level of endogenous free polyamines, particularly Put was reported by Neves et al [2002].…”

“…Root formation of apple microcuttings is influenced considerably by several medium components and other factors. Rooting efficiency enhancement was obtained by reduction of mineral salt concentration by half or even more (mainly macro-elements, especially ammonium nitrate) [Sriskandarajah et al 1990, Druart 1997 as well as medium supplementation with polyamines [Naija et al 2009], activated charcoal [Magyar-Tábori et al 2001a] and phenolic compounds [De Klerk et al 2011]. Zimmerman and Fordham [1985] proved that increased temperature to even 30°C and darkness during the induction phase lasting 3-7 days significantly enhanced shoot rooting frequency.…”

Strigolactones fine-tune the root system

“…Adventitious roots forming from Arabidopsis hypocotyls initiate from a cell layer proximate to the central cylinder and in this regard show similarity to the lateral roots that emerge from pericycle founder cells (Casimiro et al 2001). In many important crop species (including rice, maize and wheat), adventitious roots are formed via vascular cambial cell divisions whereby phloem initials start to divide to produce a primordium (Naija et al 2009) callus in which tracheids differentiate, elongate and eventually form the center of a complete root primordium (Bollmark et al 1988;Lorbiecke and Sauter 1999;Rasmussen and Hunt 2010).…”

The Physiology of Adventitious Roots

“…In many species, adventitious roots form from cambial cell divisions, which either develop directly into a new primordium or first divide into a callus tissue before tracheid differentiation and primordia establishment (Bollmark et al, 1988;Kevers et al, 1997;De Klerk et al, 1999;Naija et al, 2009;Rasmussen et al, 2009;Rasmussen and Hunt, 2010). As the root tissues form, hormone signaling changes with the restoration of higher strigolactone and cytokinin production, possibly preventing uncontrolled cell division and root initiation.…”