Increase in activity, glycosylation and expression of cytokinin oxidase/dehydrogenase during the senescence of barley leaf segments in the dark

Conrad, K.; Motyka, Václav; Schlüter, T.
PHYSIOLOGIA PLANTARUM 130 [4]: 572-579, 2007

Abstrakt: The aim of the study was to elucidate relations between senescence and cytokinin oxidase/dehydrogenase (CKX, EC Segments derived from first foliage leaves of Hordeum vulgare L. cv. Alexis were put with their bases into water and kept in darkness. Their senescence was characterized, e.g. by a 60% decline in chlorophyll within 5 days. During this time, the in vitro activity of CKX increased fast and markedly, e.g. 14-fold. Application of 10(-4) M kinetin (Kin), which slightly retarded the loss of chlorophyll, multiplied the enhancement of CKX activity strongly. Both in the presence and in the absence of Kin, the proportion of glycosylated to non-glycosylated CKX increased during senescence. By hybridization with an antisense RNA probe derived from a fragment of the CKX gene Zmckx1 of maize, an increase of the corresponding transcript of the barley gene Hvckx1 in segments incubated without Kin was shown. The content of base and riboside cytokinins slowly declined in such segments, which argues against triggering but for facilitating senescence processes by CKX.
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