Diurnal variation of cytokinin, auxin and abscisic acid levels in tobacco leaves

Abstract

As many processes are regulated by both light and plant hormones, evaluation of diurnal variations of their levels may contribute to the elucidation of the complex network of light and hormone signal transduction pathways. Diurnal variation of cytokinin, auxin, and abscisic acid levels was tested in tobacco leaves (Nicotiana tabacum L. cv. Wisconsin 38) grown under a 16/8 h 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 the 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 light/dark transition 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 the minor peak after the transition to darkness. The main, midday peak of active cytokinins was preceded by a period of minimal metabolic conversion of tritiated trans-zeatin (less than 30%). The major cytokinin-degrading enzyme, cytokinin oxidase/dehydrogenase (EC 1.5.99.12), exhibited maximal activity after the dark/light transition and during the diminishing of the midday cytokinin peak. The former peak might be connected with the elimination of the long-distance cytokinin signal. These cytokinin oxidase/dehydrogenase peaks were accompanied by increased activity of beta-glucosidase (EC 3.2.1.21), which might be involved in the hydrolysis of cytokinin O-glucosides and/or in fine-tuning of active cytokinin levels at their midday peak. The achieved data indicate that cytokinin metabolism is tightly regulated by the circadian clock.

The Plant Circadian Clock: From a Simple Timekeeper to a Complex Developmental Manager

“…The circadian regulation of several hormone signaling pathways was further confirmed by an array of other studies (Thain et al 2004;Bancos et al 2006;Covington and Harmer 2007;Mizuno and Yamashino 2008;Arana et al 2011;Shin et al 2012;Wang et al 2014;Zheng et al 2015). Furthermore, diel oscillations in phytohormone abundance have been determined (Thain et al 2004;Nováková et al 2005;Robertson et al 2009). Conversely, exogenously added cytokinin, auxin, brassinosteroids (BR), or abscisic acid (ABA), modifies at least one clock parameter, indicating that these molecules modulate the core oscillator activity (Hanano et al 2006).…”

The effectiveness of zinc in alleviating salinity stress on pistachio seedlings

“…Phytohormones were extracted and purified according to Novakova et al [25]. Frozen leaf samples (about 1 g FW) were ground in liquid nitrogen and extracted overnight with 10 cm 3 methanol/water/formic acid (15/4/1, by vol., pH ∼ 2.5, -20…”

TIME FOR COFFEE Represses Accumulation of the MYC2 Transcription Factor to Provide Time-of-Day Regulation of Jasmonate Signaling in Arabidopsis

“…A major part of phytohormone production, biosynthesis, and response gene expression oscillates under the control of diurnal signals and/or the circadian clock (Thain et al, 2004;Nováková et al, 2005;Salomé et al, 2006;Covington and Harmer, 2007;Yin et al 2007;Covington et al, 2008;Michael et al, 2008;Mizuno and Yamashino, 2008;Robertson et al, 2009;Goodspeed et al, 2012). Thereby, an array of hormone-signaling systems function as key circadian output pathways.…”