Effects of phenolic compounds on adventitious root formation and oxidative decarboxylation of applied indoleacetic acid in Malus ‘Jork 9’

Abstract

Stem slices (1-mm thick) cut from apple microshoots were cultured on a modified Murashige-Skoog medium with indole-3-acetic acid (IAA) or a-naphthaleneacetic acid (NAA), and increasing concentrations of various phenolic compounds. Both auxins were added at a concentration suboptimal for rooting. Indole-3-acetic acid is metabolized through oxidation and conjugation but NAA through conjugation only; which might have affected the results. With IAA, all tested orthodiphenols, paradiphenols and triphenols promoted adventitious root formation from the stem slices. Ferulic acid (FA, a methylated orthodiphenol) had the largest effect and increased the number of adventitious roots from 0.9 to 5.8. With NAA there was little or no promotion after addition of phenolics. Phloroglucinol (a triphenol) and FA were examined in detail. Their effects on the dose-response curve of IAA and the timing of their action indicated that both acted as antioxidants protecting IAA from decarboxylation and the tissue from oxidative stress. Experiments with carboxyl-labelled IAA showed that IAA was massively decarboxylated by the slices and that decarboxylation was strongly reduced by phenolics. Decarboxylation was to a great extent attributable to the wound response and did not occur to such an extent in non-wounded plant tissues. In shoots, FA promoted little rooting. Slices were cultured on top of the medium and shoots were stuck into the medium. Possibly, the anaerobic conditions in the medium near the basal part of the stem of shoots reduced the wound response and consequently decarboxylation of IAA. The monophenolic compound salicylic acid (SA) promoted IAA decarboxylation. Accordingly, SA reduced rooting when added during the initial days of the rooting process (the period during which auxin enhances rooting), and promoted outgrowth of root primordia later on (the period during which auxin inhibits rooting).

The Physiology of Adventitious Roots

“…More recently, however, it has been suggested that auxin degradation may also be responsible for changes in the rooting ability of pea or Prunus spp. cuttings (Liao et al, 2010;De Klerk et al, 2011;Osterc and Štampar, 2011;Rasmussen et al, 2015). De Klerk and others (2011) found that, at optimal concentrations of many of the phenolics tested, auxin degradation by decarboxylation was almost completely blocked, resulting in higher active auxin levels (Fig.…”

Physiological and developmental problems encountered by in vitro cultured plants

“…The problems range from abnormal growth to increased genetic variability/instability. Papers in this Special Issue report on micropropagation problems related to developmental and physiological aspects such as shoot-tip necrosis (Bairu et al 2011a), fasciation (Iliev and Kitin 2011), tissue proliferation (Brand 2011), epigenetic changes (Smulders and De Klerk 2011), somaclonal variation (Bairu et al 2011b), effect of phenolics on rooting (De Klerk et al 2011), alleviating problems related to caulogenic and rhizogenic processes (Moyo et al 2011) and assessment of the role of metatopolins in micropropagation and the control of culture abnormalities (Amoo et al 2011). …”

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

“…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.…”