Anatomy of Adventitious Root Formation in Microcuttings of Malus domestica Borkh. `Gala'

Abstract

Anatomical events of adventitious root formation in response to root induction medium, observing changes during induction and post-induction stages, were made with microcuttings of 'Gala' apples. Shoot explants on root induction medium containing water, 1.5 µM IBA, 44 mM sucrose, or 1.5 µM IBA + 44 mM sucrose after 4 days of treatment averaged 0, 0.2, 2.2, and 11.9 meristemoids per microcutting, respectively. Meristemoids formed in response to sucrose were confined to leaf gaps and traces. Time-course analysis of root induction with 1.5 µM IBA + 44 mM sucrose over 4 days revealed that some phloem parenchyma cells became densely cytoplasmic, having nuclei with prominent nucleoli within 1 day; meristematic activity in the phloem was widespread by 2 days; continued division of phloem parenchyma cells advanced into the cortex by 3 days; and that identifiable root primordia were present by 4 days. Cell division of pith, vascular cambium, and cortex did not lead to primordia formation. Meristematic activity was confined to the basal 1 mm of microcuttings. Timecourse analysis of post-induction treatment revealed differentiation of distinct cell layers at the distal end of primordia by 1 day; primordia with a conical shape and several cell layers at the distal end by 2 to 3 days; roots with organized tissue systems emerging from the stem by 4 days; and numerous emerged roots by 6 days. Root initiation was detectable within 24 hours and completed by day 4 of the root induction treatment and involved only phloem parenchyma cells. Chemical names used: 1 H -indole3-butryic acid (IBA).

Biology of Root Formation and Development

“…The medial zone of microcuttings roots of Cm and CT had lower diameters that seedlings. A continuous xylematic connection between the in vitro neo-formed root and the stem was observed in both species, as reported by Apter et al (1993) and Harbage et al (1993). Root growth rate was initially higher in seedlings than in in vitro rooted microcuttings of both species.…”

Reviewing current knowledge on olive (Olea europaea L.) adventitious root formation

“…Despite some differences in timing, the cytological events observed in olive by Macedo et al (2013), are in accordance with observations made in other temperate fruit species like Malus pumila 'KSC-3' (Hicks, 1987), Prunus avium x Prunus pseudocerasus (Ranjit et al, 1988), or Castanea sativa (Gonçalves et al, 1998). Timing differences were expected as the time required for root initiation varies among species from two to eight days (Auderset et al, 1994;Bressan et al, 1982;Gonçalves et al, 1998;Harbage et al, 1993;Ranjit et al, 1988;Samartin et al, 1986;San-José et al, 1992). Studies performed in apple (Hicks, 1987;Naija et al, 2008;Zhou et al, 1992), chestnut (Gonçalves et al, 1998;Vieitez et al, 1981), oak (Quercus robur) (San-José et al, 1992),…”

Ethylene Does Not Promote Adventitious Root Initiation on Apple Microcuttings

“…Root initiation treatment consisted of treating the basal end of five-node, 30-to 35day-old apical shoot microcuttings with liquid root initiation medium containing 1.5 µM IBA and 44 mM sucrose (pH 5.6). Dark incubation at 30 °C for 4 d (unless specified) was used to promote adventitious root primordia formation (Harbage et al, 1993).…”

“…After root initiation, root development treatment consisted of treating microcutting basal ends with liquid half-strength MS minerals (minus Fe) and 22 mM sucrose. Development occurred under continuous 30 µmol·m -2 ·s -1 cool-white fluorescent light at 23 °C (Harbage et al, 1993). Roots were counted after 14 d.…”