Journal
SCIENTIA HORTICULTURAE
Volume 204, Issue -, Pages 41-53Publisher
ELSEVIER
DOI: 10.1016/j.scienta.2016.03.029
Keywords
Indole-3-acetic acid (IAA); Indole-3-butyric acid (IBA); Oxidative enzymes; Phenylpropanoid biosynthetic pathway; Salicylhydroxamic acid (SHAM)
Categories
Funding
- Portuguese Foundation for Science and Technology (FCT) [PTDC/AGR-AM/103377/2008, PEst-C/AGR/UI0115/2011, SFRH/BD/80513/2011]
- Portuguese Foundation for Science and Technology (FCT) through the Programa Operational Regional do Alentejo (InAlentejo) Operation [ALENT-07-0262-FEDER-001871]
- FEDER funds through the Competitiveness Factors Operational Program (COMPETE)
- American Department of Energy (DOE) [DE-FG02-93ER20097]
- Fundação para a Ciência e a Tecnologia [SFRH/BD/80513/2011] Funding Source: FCT
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The activity of oxidative enzymes and the levels of free auxins were determined during adventitious root formation in olive explants. Rooting trials were performed both with in vitro-cultured microshoots of the cultivar 'Galega Vulgar', treated with indole-3-butyric acid (IBA) and with salicylhydroxamic acid (SHAM) + IBA, as well as with semi-hardwood cuttings of the cultivars 'Galega Vulgar' (difficult-to-root) and 'Cobrancosa' (easy-to-root), treated with IBA. The auxin (IBA) was used in all experiments as a rooting promoter, while SHAM was used in micropropagation trials as rooting inhibitor, providing a negative control. Free indole-3-acetic acid (IAA) and IBA concentrations were determined in microshoots, as well as in semi-hardwood cuttings, throughout the rooting period at pre-established time-points. At the same time-points, the enzymatic activity of polyphenol oxidases (PPO), peroxidases (PDX), and IAA oxidase (IAAox) was evaluated in the microshoots. Microshoots treated with SHAM + IBA revealed higher PDX and IAAox activity, as well as lower PPO activity, than those treated only with IBA. IAA levels were higher in IBA-treated microshoots during induction phase, but lower during early initiation phase. In contrast, free IBA levels were higher in microshoots treated with SHAM + IBA during induction, but lower during initiation. A similar pattern of free auxin levels was observed in semi-hardwood cuttings of the two contrasting cultivars under evaluation. The similarities found on the auxin patterns of microshoots treated with SHAM and those of semi-hardwood cuttings of the difficult-to-root olive cultivar allow considering SHAM a reliable control for when simulation of a difficult-to-root behavior is necessary. The inhibitory effect of SHAM in root formation could be related with 1) the inhibition of alternative oxidase (AOX), leading to a downregulation of phenylpropanoid biosynthetic pathways, which would decrease the concentration of phenolic substrates for PPO; 2) an increase in IAAox activity resulting in lower free IAA levels or; 3) a defective conversion of IBA into IAA. (C) 2016 Elsevier B.V. All rights reserved.
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