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Cyto kinins in xanthium strumarium some aspects of the photoperiodic control of endogenous levels



Cyto kinins in xanthium strumarium some aspects of the photoperiodic control of endogenous levels



New Phytologist 78(1): 35-45



The effects of photoperiod on cytokinin levels in X. strumarium were examined using a single photoperiodic cycle. Increasing the night length from 6 to 16 h resulted in a progressive decline in cytokinin levels in leaf laminae and buds. Interruption of a 16-h dark period midway by either a 5- or 60-min light-break at least partially negated the depressive effect of the dark period on cytokinin levels. All peaks of cytokinin activity were similarly affected by short day treatment. The reduction of cytokinin levels in response to a long dark period was dependent upon the presence of leaves greater than 1.0 cm in length but not upon the presence of buds. While exposure of the entire plant to a single long dark period led to a marked reduction in cytokinin levels in the leaf laminae, no such reduction was apparent in leaves which were exposed individually to a long night (with the rest of the plant, including the majority of the leaves, left in long day). The latter treatment did lead to a partial reduction in the cytokinin flux from the detopped root system. Bark ringing of the stem between roots and leaves prior to photoperiodic treatment largely prevented the short day-induced decline in cytokinin levels in both leaf laminae and root exudate. These results are taken to indicate the existence of a shoot-to-root signal capable of moderating cytokinin production in the root system.

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Accession: 005082601

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