Affiliations: Institute of Experimental Botany, Academy of Sciences
of CR, Charles University, Prague, Czech Republic | Institute of Medical Chemistry and Biochemistry,
Charles University, Prague, Czech Republic | Institute of Physiology, 2nd Medical Faculty, Charles
University, Prague, Czech Republic
Note: [] Address for correspondence: Dr. Nad'a Wilhelmová,
Department of Stress Physiology, Institute of Experimental Botany, Academy of
Sciences of the Czech Republic, Na Karlovce 1a, 160 00 Prague 6, Czech
Republic. Tel.: +420 224 310 109; Fax: +420 224 310 113; E-mail:
wilhelmova@ueb.cas.cz
Abstract: Transgenic plants with genetically increased or decreased levels of
cytokinins were used to investigate the effect of cytokinin level on the
production of ethylene, a plant hormone with suggested role in senescence, and
the production of nitric oxide, potentially important signalling and regulatory
molecule. The production of these gases was followed during the course of leaf
development and senescence. The production of ethylene and nitric oxide is
under genetic control of genes other than those involved in regulation of
senescence. The difference in basic ethylene and NO levels in different tobacco
cultivars was higher than their changes in senescence. The results of this
study did not indicate a direct link between ethylene production and cytokinin
levels. However, there was a decreased production of NO in senescent leaves.
Low cytokinins level was associated with increased NO production during leaf
development. Protein nitrotyrosine proved to be a better indicator of the
reactive nitrogen species than measuring of the NO production. Higher
nitrotyrosine concentrations were found in insoluble proteins than in the
soluble ones, pointing to membrane proteins as the primary targets of the
reactive nitrogen species. In plants with elevated cytokinin levels the content
of nitrated proteins decreased both in soluble and insoluble fractions. This
finding indicates an antioxidative function of cytokinins against reactive
nitrogen species.
