Cytokinins or cytokinins are a group of plant hormones with multiple effects on the growth and development of plants . Its name is derived from its stimulating effect on cytokinesis ( Greek kytos = cell and kinesis = movement ). The cytokinins are present as phytohormones in all plants, but are also found in animal tissues as well as in bacteria , fungi and algae . Cytokinins are present in plant tissue in free form or bound in specific transfer ribonucleic acids (tRNA) . The concentration of cytokinins in plant tissue is extremely low and depends on the plant organ and its level of development.
The most important natural cytokinins are cis - and trans - zeatin , zeatin riboside and ribotide , dihydroceatin and N 6 -isopentenyladenine , as well as other derivatives of adenine with an isoprenoid C5 side chain (R) on the exocyclic nitrogen atom N6.
Zeatin was the first natural cytokinin to be isolated from unripe corn kernels and is widespread in higher plants. In addition to this basic cytokinin, corresponding ribonucleosides (9-ribosides) and ribonucleotides (9-riboside-5'-monophosphates) as well as N-7 or N-9 and O-4 glucosides also occur in plants.
Of the synthetic cytokinins, the so-called organic compounds with cytokinine activity, kinetin (6-furfurylaminopurine) and benzylaminopurine (6-benzyladenine) as well as some N , N -diphenylurea derivatives are of particular importance, e.g. B. Kinetin in phytohormone research as a model substance.
The first step in cytokinin biosynthesis is the transfer of an isopentenyl group ( dimethylallyl pyrophosphate / DMAPP, 1-hydroxy-2-methyl-2- ( E ) -butenyl-4-diphosphate / HMBDP) to an adenosine unit ( ATP / ADP / AMP ). In plants there is a transfer of DMAPP to ATP / ADP, bacteria such. B. Agrobacterium tumefaciens, however, transfer HMBDP to AMP. The steps are enzymatically catalyzed by various IPTs (isopentenyl transferases).
The biosynthesis of natural cytokinins is closely related to the RNA - metabolism connected and is provided either de novo from low molecular weight compounds on the purine ring cytokininhaltiger or by release of cytokinins by the degradation of t-RNA. The main biosynthesis site is the root tip as well as young fruits and seeds . The transport takes place in the xylem (conductive tissue).
The effects of the cytokinins overlap with those of other phytohormones. The stimulation of cytokinesis ( cell division , mitosis ) in callus tissues and the promotion of elongation growth of the plant are characteristic.
Cytokinins regulate in close interaction with other phytohormones, especially the auxins and abscisic acid , and environmental factors e.g. B. Light diverse plant growth and differentiation processes. This also includes delaying the aging process in plants.
While the effect of cytokinins in vascular plants often called pleiotropic describes induce the protonema of mosses the bud formation . This transition from the apical growth (apical growth) for growth by means of three-edged apical cell goes to the differentiation capacity of a single cell back and represents a specific cytokinin.
Current studies have described the role of cytokinins in plant defense. For example, it could be shown that cytokinins induce resistance to Pseudomonas syringae in Arabidopsis thaliana and Nicotiana tabacum . In addition, the production of cytokinins by Pseudomonas fluorescens has been shown to be a determinant of biological control of plant diseases.
- Lincoln Taiz: Plant Physiology: The Original with Translation Aids (Sav Biologie) (German Edition) . Spectrum Akademischer Verlag 2007, ISBN 978-3-8274-1865-4 , pp. 550–551.
- EL Decker, W. Frank, E. Sarnighausen, R. Reski : Moss Systems Biology en Route: Phytohormones in Physcomitrella Development . In: Plant Biology . tape 8 , no. 3 , May 2006, pp. 397-406 , doi : 10.1055 / s-2006-923952 ( PDF ). PDF ( Memento of the original from July 2, 2016 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
- Jaemyung Choi, Sung Un Huh, Mikiko Kojima, Hitoshi Sakakibara, Kyung-Hee Paek, Ildoo Hwang ,: The Cytokinin-Activated Transcription Factor ARR2 Promotes Plant Immunity via TGA3 / NPR1-Dependent Salicylic Acid Signaling in Arabidopsis . In: Developmental Cell . tape 19 , no. 2 , 2010, p. 284-295 , doi : 10.1016 / j.devcel.2010.07.011 .
- Dominik K. Großkinsky, Muhammad Naseem, Usama Ramadan Abdelmohsen, Nicole Plickert, Thomas Engelke, Thomas Griebel, Jürgen Zeier, Ondřej Novák, Miroslav Strnad, Hartwig Pfeifhofer, Eric van der Graaff, Uwe Simon, Thomas Roitsch: Cytokinins Mediate Resistance against Pseudomonas syringae in Tobacco through Increased Antimicrobial Phytoalexin Synthesis Independent of Salicylic Acid Signaling . In: Plant Physiology . tape 157 , no. 2 , October 1, 2011, p. 815-830 , doi : 10.1104 / pp.111.182931 , PMC 3192561 (free full text).
- Dominik K. Großkinsky, Richard Tafner, María V. Moreno, Sebastian A. Stenglein, Inés E. García de Salamone, Louise M. Nelson, Ondřej Novák, Miroslav Strnad, Eric van der Graaff, Thomas Roitsch: Cytokinin production by Pseudomonas fluorescens G20-18 determines biocontrol activity against Pseudomonas syringae in Arabidopsis . In: Scientific Reports . tape 6 , March 17, 2016, doi : 10.1038 / srep23310 , PMC 4794740 (free full text).