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Published on September 28, 2007; 10.1104/pp.107.103176

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Received June 6, 2007
Accepted September 21, 2007

Cytokinins in the Bryophyte Physcomitrella Patens: Analyses of Activity, Distribution, and Cytokinin Oxidase/Dehydrogenase Overexpression Reveal Role of Extracellular Cytokinins

Klaus von Schwartzenberg *, Marta Fernandez Nunez , Hanna Blaschke , Petre I. Dobrev , Ondrej Novak , Vaclav Motyka , and Miroslav Strnad

Biozentrum Klein Flottbek, Universitat Hamburg, Ohnhorststr. 18, D-22609 Hamburg, Germany; Laboratory of Growth Regulators, Palacky University & Institute of Experimental Botany, Academy of Sciences of the Czech Republic, Slechtitelu 11, CZ-78371 Olomouc, Czech Republic; Institute of Experimental Botany, Academy of Sciences of the Czech Republic, Rozvojova 263, CZ-16502 Prague 6, Czech Republic

* Corresponding author; email: kvschwartzenberg{at}botanik.uni-hamburg.de.

Ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) was used to establish the cytokinin profile of the bryophyte Physcomitrella patens (Hedw.) B.S.G. and of 40 analysed cytokinins, 20 were detected. Cis-zeatin-riboside-O-glucoside, N6-({Delta}2-isopentenyl)adenosine-5'-monophosphate (iPRMP) and trans-zeatinriboside-O-glucoside were the most abundant intracellular cytokinins. In addition, the aromatic cytokinins N6-benzyladenosine (BAR), N6-benzyladenine (BA), meta- and ortho-topolin (mT, oT) were detected. Unexpectedly, the most abundant extracellular cytokinin was the nucleotide iPRMP and its identity was confirmed by Q-Tof mass spectrometry. The effects of overexpressing a heterologous cytokinin oxidase/dehydrogenase (CKX, EC 1.4.3.18/1.5.99.12) gene (AtCKX2 from Arabidopsis thaliana) on the intra- and extra-cellular distribution of cytokinins was assessed. In cultures of CKX-transformed plants UPLC-MS/MS measurements showed that there were pronounced reductions in the extracellular concentrations of N6-({Delta}2-isopentenyl)adenine (iP) and N6-({Delta}2-isopentenyl)adenosine (iPR), but their intracellular cytokinin concentrations were only slightly affected. In vitro and in vivo measured CKX activity was shown to be strongly increased in the transformants. Major phenotypic changes observed in the CKX-overexpressing plants included reduced and retarded budding, absence of sexual reproduction and abnormal protonema cells. In bud induction bioassays with wild type Physcomitrella the nucleotides iPRMP, tZRMP, BARMP, and the cis-zeatin forms cZ and cZR had no detectable effects, while the activities displayed by other selected cytokinins were in the following order: iP>tZ>BA>BAR>iPR>tZR>mT>DHZ>oT. The results on wild type and CKX transgenics suggest that extracellular iP and iPR are the main cytokinins responsible for inducing buds in the bryophyte Physcomitrella. Cytokinin profile is dicussed regarding the evolution of cytokinin biosynthetic pathways.




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B. Pils and A. Heyl
Unraveling the Evolution of Cytokinin Signaling
Plant Physiology, October 1, 2009; 151(2): 782 - 791.
[Abstract] [Full Text] [PDF]


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