No abstract

Phytohormones are important regulators of numerous developmental and physiological processes in plants. Spontaneous morphogenesis of the common centaury (Centaurium erythraea Rafn.) is possible on nutrition medium without addition of any plant growth regulator depending solely on endogenous phytohormone levels. Thus, this plant species represents a very good model system for the investigation of numerous physiological processes under phytohormonal control in vitro. We analysed the total amount of endogenous cytokinins (CKs) including the contents of their individual groups in shoots and roots of C. erythraea plants grown in vitro. The total amount of endogenous CKs was 1.4 times higher in shoots than in roots. Inactive or weakly active N-glucosides found to predominate in both organs of centaury plants, whereas free bases and O-glucosides represented only a small portion of the total CK pool. Consequently, centaury roots showed higher IAA content as well as IAA/ free CK base ratios compared to shoots. Centaury tissues also showed increased levels of ''stress hormones''. In contrast to SA, considerably higher levels of ABA were found in centaury shoots than in roots. Our results could serve as a basis for understanding and elucidating spontaneous de novo shoot organogenesis and further plant regeneration of C. erythraea in vitro. Abbreviations for CKs Adopted and Modified According to Kamínek and Others (2000) ADPAdenosine diphosphate AMP Adenosine monophosphate CK Cytokinin cisZ cis-zeatin cisZ7G cis-zeatin 7-glucoside cisZ9G cis-zeatin 9-glucoside cisZOG cis-zeatin O-glucoside cisZR cis-zeatin 9-riboside cisZRMP cis-zeatin 9-riboside-5 0 -monophosphate cisZROG cis-zeatin 9-riboside O-glucoside DHZ Dihydrozeatin DHZ7GDihydrozeatin 7-glucoside DHZ9GDihydrozeatin 9-glucoside DHZOG Dihydrozeatin O-glucoside DHZR Dihydrozeatin 9-riboside DHZRMP Dihydrozeatin 9-riboside-5 0 -monophosphate DHZROG Dihydrozeatin 9-riboside O-glucoside iP N 6 -(D 2 -isopentenyl)adenine iP7G N 6 -(D 2 -isopentenyl)adenine 7-glucoside iP9G N 6 -(D 2 -isopentenyl)adenine 9-glucoside iPR N 6 -(D 2 -isopentenyl)adenine 9-riboside Milana Trifunović-Momčilov and Václav Motyka have contributed equally to this work. Electronic supplementary materialThe online version of this article (iPRMP N 6 -(D 2 -isopentenyl)adenine 9-riboside-5 0 -monophosphate transZ trans-zeatin transZ7Gtrans-zeatin 7-glucoside transZ9G trans-zeatin 9-glucoside transZOG trans-zeatin O-glucoside transZR trans-zeatin 9-riboside transZRMP trans-zeatin 9-riboside-5 0 -monophosphate transZROG trans-zeatin 9-riboside O-glucoside

Common centaury (Centaurium erythraea Rafn.) is a plant species that can inhabit saline soils. It is known as plant with high spontaneous regeneration potential in vitro. In present work we evaluated shoots and roots salinity tolerance of non transformed and three AtCKX transgenic centaury lines to graded NaCl concentrations (0, 50, 100, 150, 200 mM) in vitro. Overexpression of AtCKX genes in transgenic centaury plants resulted in an altered cytokinins (CKs) profile leading to a decline of bioactive CK levels and, at the same time, increased contents of storage CK forms, inactive CK forms and/or CK nucleotides. Significant increment of fresh shoot weight was obtained in shoots of non transformed and AtCKX1 transgenic line only on medium supplemented with 50 mM NaCl. However two analyzed AtCKX2 transgenic lines reduced shoot growth at all NaCl concentrations. In general, centaury roots showed higher tolerance to salinity than shoots. Non transformed and AtCKX1 transgenic lines tolerated up to 100 mM NaCl without change in frequency of regeneration and number of regenerated plants. Roots of two analyzed AtCKX2 transgenic lines showed different regeneration potential under salt stress. Regeneration of transgenic AtCKX2-26 shoots even at 200 mM NaCl was recorded. Salinity stress response of centaury shoots and roots was also evaluated at biochemical level. Free proline, malondialdehyde and hydrogen peroxide content as well as antioxidative enzymes activities were investigated in shoots and roots after 1, 2, 4 and 8 weeks. In general, adition of NaCl in culture medium elevated all biochemical parametars in centaury shoots and in roots. Considering that all analyzed AtCKX transgenic centaury lines showed altered salt tolerance to graded NaCl concentrations in vitro it can be assumed that CKs might be involved in plant defence to salt stress conditions.

No abstract

No abstract