JXB Advance Access originally published online on May 31, 2008
Journal of Experimental Botany 2008 59(10):2659-2672; doi:10.1093/jxb/ern134
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© 2008 The Author(s).
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.0/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
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RESEARCH PAPER |
Cytokinin deficiency causes distinct changes of sink and source parameters in tobacco shoots and roots
Werner1 *
1Institute of Biology/Applied Genetics, Free University of Berlin, Berlin, Germany
2Institute of Biology/Plant Physiology, Humboldt University Berlin, Berlin, Germany
3Cytologie Expérimentale et Morphogenèse Végétale (CEMV), Université Pierre et Marie Curie, Paris, France
To whom correspondence should be addressed. E-mail: tschmue{at}zedat.fu-berlin.de
Cytokinin deficiency causes pleiotropic developmental changes such as reduced shoot and increased root growth. It was investigated whether cytokinin-deficient tobacco plants, which overproduce different cytokinin oxidase/dehydrogenase enzymes, show changes in different sink and source parameters, which could be causally related to the establishment of the cytokinin deficiency syndrome. Ultrastructural analysis revealed distinct changes in differentiating shoot tissues, including an increased vacuolation and an earlier differentiation of plastids, which showed partially disorganized thylakoid structures later in development. A comparison of the ploidy levels revealed an increased population of cells with a 4C DNA content during early stages of leaf development, indicating an inhibited progression from G2 to mitosis. To compare physiological characteristics of sink leaves, source leaves and roots of wild-type and cytokinin-deficient plants, several photosynthetic parameters, content of soluble sugars, starch and adenylates, as well as activities of enzymes of carbon assimilation and dissimilation were determined. Leaves of cytokinin-deficient plants contained less chlorophyll and non-photochemical quenching of young leaves was increased. However, absorption rate, photosynthetic capacity (Fv/Fm and JCO2max) and efficiency (
CO2app), as well as the content of soluble sugars, were not strongly altered in source leaves, indicating that chlorophyll is not limiting for photoassimilation and suggesting that source strength did not restrict shoot growth. By contrast, shoot sink tissues showed drastically reduced contents of soluble sugars, decreased activities of vacuolar invertases, and a reduced ATP content. These results strongly support a function of cytokinin in regulating shoot sink strength and its reduction may be a cause of the altered shoot phenotype. Roots of cytokinin-deficient plants contained less sugar compared with wild-type. However, this did not negatively affect glycolysis, ATP content, or root development. It is suggested that cytokinin-mediated regulation of the sink strength differs between roots and shoots.
Key words: Carbohydrates, cell cycle, cytokinin, cytokinin deficiency, differentiation, invertase, meristem, photosynthesis, sink, source
* These authors have contributed equally to this work.
Received 20 December 2007; Revised 19 March 2008 Accepted 7 April 2008
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