Cytokinins (CKs) are phytohormones regulating plant growth and development as well as response to the environment. In order to evaluate their function in heat stress (HS) responses, the effect of CK elevation was determined during three types of HS - targeted to shoots, targeted to roots and applied to the whole plant. The early (30min) and longer term (3h) responses were followed at the hormonal, transcriptomic and proteomic levels in Arabidopsis transformants with dexamethasone-inducible expression of the CK biosynthetic gene isopentenyltransferase (ipt) and the corresponding wild-type (Col-0). Combination of hormonal and phenotypic analyses showed transient up-regulation of the CK/abscisic acid ratio, which controls stomatal aperture, to be more pronounced in the transformant. HS responses of the root proteome and Rubisco-immunodepleted leaf proteome were followed using 2-D gel electrophoresis and MALDI-TOF/TOF. More than 100 HS-responsive proteins were detected, most of them being modulated by CK increase. Proteome and transcriptome analyses demonstrated that CKs have longer term positive effects on the stress-related proteins and transcripts, as well as on the photosynthesis-related ones. Transient accumulation of CKs and stimulation of their signal transduction in tissue(s) not exposed to HS indicate that they are involved in plant stress responses.

Institute of Plant Molecular Biology Biology Centre AS CR Branišovská 31 1160 370 05 České Budějovice Czech Republic

Laboratory of Hormonal Regulations in Plants Institute of Experimental Botany AS CR Rozvojová 263 165 02 Praha Czech Republic

Laboratory of MS Faculty of Science Charles University Viničná 7 CZ 128 43 Prague Czech Republic

Laboratory of Plant Molecular Biology Institute of Biophysics AS CR v v i and Mendel University in Brno CEITEC Central European Institute of Technology Mendel University in Brno Zemědělská 1 CZ 613 00 Brno Czech Republic

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