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Abstract Detail


Hormone Biology

Sýkorová, Blanka [1], Motyka, Václav [1], Raimanová, Ivana [2], Hoyerová, Klára [1], Trčková, Marie [2], Dobrev, Petre [1], Kamínek, Miroslav [3].

Cytokinin oxidase/dehydrogenase activity in oat xylem sap and its responses to exogenous nitrate.

The concentration of bioactive cytokinins in apoplast can be potentially modulated by extracellular cytokinin metabolism and cytokinin uptake. Addressing this issue we found the cytokinin oxidase/dehydrogenase (CKX) activity in xylem sap from oat plants. The enzyme exhibited pH optimum at 8.5 and its activity was associated with glycosylated protein. As the pH of root-sourced xylem sap is much lower (6.1) the activity of the CKX leaving the roots seems to be suppressed protecting the co-transported cytokinins from degradation. Testing the potential role of CKX in control of cytokinin concentration in root xylem exudates in response to environmental signals we exposed 14-d old oat plants for 48 h to nutrient solutions differing in NO3- concentration (16 - 1000 µM). The flux of the root-sourced CKX activity was increasing with increasing of NO3- supply up to 7-fold correlating well with increasing flux of bioactive cytokinins [trans-zeatin riboside, trans-zeatin and N6-(2-isopentenyl)adenine]. Interestingly, the flux of corresponding cis-isomers of zeatin, which exhibit very low cytokinin activity, was, with exception of cis-zeatin O-glucoside, not affected by the exogenous NO3-. Correspondingly, the accumulation of trans-zeatin and trans-zeatin riboside in roots and shoots was more than 2-fold increased in response to NO3- supply while the content of corresponding cis-isomers was lowered indicating different regulation of biosynthesis of these two isomers by nitrate. Results are discussed in relation to recently reported alkalization of xylem sap during its flow from roots to shoots and cytokinin accumulation at sites of high transpiration suggesting potential involvement of root-sourced CKX in down-regulation of co-transported cytokinins in the leaf apoplast.


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1 - Institute of Experimental Botany, Academy of Sciences, Hormonal Regulations in Plants
2 - Crop Research Institute, Department of Plant Physiology
3 - Institute of Experimental Botany, Hormonal Regulations in Plants, Rozvojová 135, Prague 6, CZ-165 02, Czech Republic

Keywords:
Cytokinin
cis- and trans-zeatin
nitrate
root xylem sap.

Presentation Type: Plant Biology Abstract
Session: P
Location: Exhibit Hall (Northeast, Southwest & Southeast)/Hilton
Date: Sunday, July 8th, 2007
Time: 8:00 AM
Number: P35022
Abstract ID:410


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