Circadian changes in endogenous concentrations of indole-3-acetic acid, melatonin, serotonin, abscisic acid and jasmonic acid in Characeae (Chara australis Brown)

Abstract

Giant-celled Characeae (Chara australis Brown), grown for 4 months on 12/12 hr day/night cycle and summer/autumn temperatures, exhibited distinct concentration maxima in auxin (indole-3-acetic acid; IAA), melatonin and serotonin about 4 hr after subjective daybreak. These concentration peaks persisted after 3 day pretreatment in continuous darkness: confirming a circadian rhythm, rather than a response to "light on." The plants pretreated for 3 d in continuous light exhibited several large IAA concentration maxima throughout the 24 hr. The melatonin and serotonin concentrations decreased and were less synchronized with IAA. Chara plants grown on 9/15 hr day/night cycle for 4 months and winter/spring temperatures contained much smaller concentrations of IAA, melatonin and serotonin. The IAA concentration maxima were observed in subjective dark phase. Serotonin concentration peaks were weakly correlated with those of IAA. Melatonin concentration was low and mostly independent of circadian cycle. The "dark" IAA concentration peaks persisted in plants treated for 3 d in the dark. The plants pretreated for 3 d in the light again developed more IAA concentration peaks. In this case the concentration maxima in melatonin and serotonin became more synchronous with those in IAA. The abscisic acid (ABA) and jasmonic acid (JA) concentrations were also measured in plants on winter regime. The ABA concentration did not exhibit circadian pattern, while JA concentration peaks were out of phase with those of IAA. The data are discussed in terms of crosstalk between metabolic pathways.

Keywords: Characeae; abscisic acid; circadian rhythm; indole-3-acetic acid; jasmonic acid; melatonin; metabolic pathways; serotonin.

Figure 1.

Chara australis plant (male, identified by orange antheridia). Scale bar = 50 mm. The circle shows the top part of the plant used in sampling (adapted from Beilby & Casanova).

Figure 2.

Diurnal concentration of IAA (green), melatonin (red) and serotonin (blue) in characean plants acclimated to different photoperiodic regimes: (A) 12/12 light/dark cycle, the gray rectangles indicate darkness (B) Explants pretreated 3 d in darkness, the dashed line rectangles indicate where plants experienced dark in the 12/12 hour regime, (C) Explants pretreated 3 d in light, the dashed line rectangles indicate where plants experienced dark in the 12/12 hour regime. Bars indicate standard error of the triplicate analysis of each sample.

Figure 3.

Diurnal concentration of IAA (green), melatonin (red) and serotonin (blue) in characean plants acclimated to different photoperiodic regimes: (A) 9/15 light/dark cycle, the gray rectangles indicate darkness. The melatonin and serotonin concentrations were low compared to IAA concentration and were multiplied by 100 and 20, respectively, to be visible on the graph (see Table 1b for the values of the concentration maxima). (B) Explants pretreated 3 d in darkness, the dashed line rectangles indicate where plants experienced dark in the 9/15 hour regime. Melatonin and serotonin concentrations were multiplied by 10 and 20, respectively, to be visible on the graph (see Table 1b for the values of the concentration maxima). (C) Explants pretreated 3 d in light, the dashed line rectangles indicate where plants experienced dark in the 9/12 hour regime. Melatonin and serotonin concentrations were multiplied by 50 and 50, respectively, to be visible on the graph (see Table 1b for the values of the concentration maxima).

Figure 4.

Diurnal concentration of IAA (green), JA (blue) and ABA (red) in characean plants acclimated to different photoperiodic regimes: (A) 9/15 light/dark cycle, the gray rectangles indicate darkness. (B) Explants pretreated 3 d in darkness, the dashed line rectangles indicate where plants experienced dark in the 9/15 hour regime. (C) Explants pretreated 3 d in light, the dashed line rectangles indicate where plants experienced dark in the 9/15 hour regime.

Figure 5.

Chromatographic separation of serotonin, melatonin, indole-3-acetic acid, abscisic acid, and jasmonic acid.