Novakova M., Motyka V., Dobrev P.I., Malbeck J., Gaudinova A., Vankova R.
JOURNAL OF EXPERIMENTAL BOTANY
56 (421):
2877-2883,
2005
Keywords:
abscisic acid; auxin; cytokinin; cytokinin oxidase/dehydrogenase; diurnal rhythm; beta-glucosidase; tobacco
Abstract:
As many processes are regulated by both light and cytokinins, potential involvement of cytokinins in light signal transduction pathway, manifested by direct effect of light on cytokinin metabolism, was tested in tobacco leaves (Nicotiana tabacum L. cv. Wisconsin 38) grown under 16h/8h photoperiod. The main peak of physiologically active cytokinins (cytokinin bases and ribosides) was found after 9 h of light, i.e. 1 h after the middle of light period. This peak coincided with the major auxin peak and was closely followed by a minor peak of abscisic acid. Free abscisic acid started to increase at the dusk and reached its maximum 3 h after dark initiation.
The content of total cytokinins (mainly N-glucosides, followed by cis-zeatin derivatives and nucleotides) exhibited the main peak after 9 h of light and minor peak after the transition to darkness. The main, midday peak of active cytokinins was preceded by the period of minimal metabolic conversion of tritiated trans-zeatin (less than 30%). The main cytokinin degrading enzyme, cytokinin oxidase/dehydrogenase (EC 1.5.99.12), exhibited maximal activity after dark/light transition and during diminishing of the midday cytokinin peak. The former peak might be connected with elimination of the long-distance cytokinin signal. These cytokinin oxidase/dehydrogenase peaks were accompanied with increased activity of β-glucosidase (EC 3.2.1.21.), which might be involved in hydrolysis of cytokinin O-glucosides (transport forms) and/or in fine-tuning of active cytokinin levels at their midday peak. The achieved data indicate that cytokinin metabolism is tightly regulated by circadian clock, however, not directly affected by light.
IEB authors: Radomíra Vanková
Čeština
English