Cytokinin and Ethylene Affect Auxin Transport-Dependent Rhizogenesis in Hypocotyls of Common Ice Plant (<Emphasis Type="Italic">Mesembryanthemum crystallinum</Emphasis> L<Emphasis Type="Italic">.</Emphasis>) |
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Authors: | Robert Konieczny Jan Kępczyński Maria Pilarska Danuta Cembrowska Diedrik Menzel Jozef Šamaj |
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Institution: | 1.Department of Plant Cytology and Embryology,Jagiellonian University,Kraków,Poland;2.Department of Plant Physiology and Biotechnology,University of Szczecin,Szczecin,Poland;3.Institute of Cellular and Molecular Botany,University of Bonn,Bonn,Germany;4.Institute of Plant Genetics and Biotechnology,Slovak Academy of Sciences,Nitra,Slovak Republic;5.Faculty of Natural Sciences,Palacky University,Olomouc,Czech Republic |
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Abstract: | Hypocotyl explants of Mesembryanthemum crystallinum regenerated roots when cultured vertically with either the apical end (AE) or basal end (BE) in media containing indole-3-acetic
acid (IAA). IAA alone induced roots regularly from the basal end of the explants, either from the cut surface immersed in
the medium or from the opposite side. The inhibitors of auxin efflux carriers, α-naphthylphthalamic acid (NPA) and 2,3,5-triiodobenzoic
acid (TIBA), inhibited rhizogenesis only from AE-cultured explants, indicating the role of polar auxin transport in root regeneration
in this system. Cytokinin (zeatin, kinetin, BAP) added to auxin-containing medium reduced rhizogenesis from the explants maintained
with BE and AE and additionally changed the IAA-induced pattern of rooting in AE-cultured explants by favoring rooting from
the apical end and middle part of the hypocotyl with its concomitant reduction from the basal end. The addition of kinetin
did not influence the content of IAA in the explants maintained with AE, suggesting that the cytokinin effect on root patterning
was not dependent on auxin biosynthesis. Kinetin, however, strongly enhanced ethylene production. The importance of ethylene
in regulating PAT-dependent rhizogenesis was tested by using an ethylene antagonist AgNO3, an inhibitor of ethylene synthesis aminoethoxyvinylglycine (AVG), and a precursor of ethylene, 1-aminocyclopropane-1-carboxylic
acid (ACC). AgNO3 applied together with IAA or with IAA and kinetin strongly reduced the production of ethylene, inhibited rhizogenesis, and
induced nonregenerative callus from BE, suggesting the need for ethylene signaling to elicit the rhizogenic action of auxin.
A reduction of rhizogenesis and decrease of ethylene biosynthesis was also caused by AVG. In addition, AVG at 10 μM reversed
the effect of cytokinin on root patterning, resulting in roots emerging only from BE on the medium with IAA and kinetin. Conversely,
ACC at 200 μM markedly enhanced the production of ethylene and partly mimicked the effect of cytokinin when applied with IAA
alone, thus confirming that in cultured hypocotyls of ice plant, cytokinin affects IAA-induced rhizogenesis through an ethylene-dependent
pathway. |
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