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ENVIRONMENTAL STRESS AND ADAPTATION TO STRESS

Characterization of New Maize Genes Putatively Involved in Cytokinin Metabolism and Their Expression during Osmotic Stress in Relation to Cytokinin Levels^1,[W]

árka Vyroubalová, Kateina Václavíková, Veronika Tureková, Ondej Novák, Mária mehilová, Tomá Hluska, Ludmila Ohnoutková, Ivo Frébort and Petr Galuszka^*

Department of Biochemistry (.V., K.V., M.., T.H., I.F., P.G.) and Department of Cell Biology and Genetics (L.O.), Faculty of Science, Palack University, Olomouc CZ–78371, Czech Republic; and Laboratory of Growth Regulators, Palack University, and Institute of Experimental Botany, Academy of Sciences of the Czech Republic, Olomouc CZ–78371, Czech Republic (V.T., O.N.)

Plant hormones, cytokinins (CKs), have been for a long time considered to be involved in plant responses to stress. However, their exact roles in processes linked to stress signalization and acclimatization to adverse environmental conditions are unknown. In this study, expression profiles of the entire gene families of CK biosynthetic and degradation genes in maize (Zea mays) during development and stress responses are described. Transcript abundance of particular genes is discussed in relation to the levels of different CK metabolites. Salt and osmotic stresses induce expression of some CK biosynthetic genes in seedlings of maize, leading to a moderate increase of active forms of CKs lasting several days during acclimatization to stress. A direct effect of CKs to mediate activation of stress responses does not seem to be possible due to the slow changes in metabolite levels. However, expression of genes involved in cytokinin signal transduction is uniformly down-regulated within 0.5 h of stress induction by an unknown mechanism. cis-Zeatin and its derivatives were found to be the most abundant CKs in young maize seedlings. We demonstrate that levels of this zeatin isomer are significantly enhanced during early stress response and that it originates independently from de novo biosynthesis in stressed tissues, possibly by elevated specific RNA degradation. By enhancing their CK levels, plants could perhaps undergo a reduction of growth rates maintained by abscisic acid accumulation in stressed tissues. A second role for cytokinin receptors in sensing turgor response is hypothesized besides their documented function in CK signaling.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Petr Galuszka (petr.galuszka{at}upol.cz).

^[W] The online version of this article contains Web-only data.

www.plantphysiol.org/cgi/doi/10.1104/pp.109.142489

^* Corresponding author; e-mail petr.galuszka{at}upol.cz.

Received June 5, 2009; accepted July 27, 2009; published July 29, 2009.