Circadian Rhythms of Chemotaxis to Ammonium and of Methylammonium Uptake in Chlamydomonas

Abstract

Chiamydomonas reinhardtii expresses a well-documented circadian rhythm of phototaxis, which peaks in the subjective daytime. We find that vegetative cells also express circadian rhythms of chemotaxis to ammonium and ammonium uptake (as gauged by uptake of [14C]methylammonium). The chemotaxis rhythm peaks in the subjective night. Methylammonium uptake is light dependent, and its rhythm peaks at subjective dawn. Unlike vegetative cells, gametes are not attracted to ammonium. We believe this to be the first report of a circadian rhythm of chemotaxis.The unicellular alga Chlamydomonas reinhardtii displays several circadian rhythms, including phototaxis (1) and "stickiness" to glass (24). Of these, the phototaxis rhythm has been investigated most extensively: Bruce and Bruce (2) isolated clock mutants, drugs have been assayed for their ability to phase shift the rhythm (4), and Kondo et al.(1 1) m-easured action spectra for light-induced phase resetting.Phototaxis of Chlamydomonas cells is high during the day phase ofan LD2 cycle and is low at night. This rhythm persists in DD or LL, i.e. phototaxis remains high in subjective daytime and low in the subjective night (1). The rhythm is truly a change in phototactic response per se and is not a daily change of motility (12,19

Real-Time Monitoring of Chloroplast Gene Expression by a Luciferase Reporter: Evidence for Nuclear Regulation of Chloroplast Circadian Period

“…The intracellular desynchronization of circadian oscillators has been demonstrated for the dinoflagellate Gonyaulux (38,49). It will be of interest to examine whether the chloroplast bioluminescence rhythm and other rhythms observed in Chlamydomonas (e.g., phototaxis, cell division cycle, stickiness to glass, and chemotaxis) (5,9,15,43) can be desynchronized under specific conditions. Surprisingly, the psbD-lucCP reporter strain exhibited a robust bioluminescence rhythm with sharp peaks and very low baseline even under DD on HSM agar (Fig.…”

Algal photoreceptors: in vivo functions and potential applications

“…In C. reinhardtii, vegetative cells and mating-incompetent pregametes are attracted to ammonium (Byrne et al 1992;Sjoblad and Frederikse 1981). However, at the late phase of gamete formation, exposure to light results in gaining of mating competence by a loss of chemotactic sensitivity for ammonium (Byrne et al 1992;Ermilova et al 2003). The shut-off of chemotaxis during sexual development of C. reinhardtii is mediated by blue light and it is also partially controlled by phototropin (Ermilova et al 2004).…”

“…Moreover, CrPhot is also involved in controlling changes in the sensitivity of chemotaxis during sexual differentiation (Ermilova et al 2004). In C. reinhardtii, vegetative cells and mating-incompetent pregametes are attracted to ammonium (Byrne et al 1992;Sjoblad and Frederikse 1981). However, at the late phase of gamete formation, exposure to light results in gaining of mating competence by a loss of chemotactic sensitivity for ammonium (Byrne et al 1992;Ermilova et al 2003).…”

Quantitative analysis of the chemotaxis of a green alga, Chlamydomonas reinhardtii, to bicarbonate using diffusion-based microfluidic device

“…4 A deeper understanding of algal physiology is crucial for the realization of biotechnological application of microalgae. 5,6 There have been a number of studies on the physiology related to photosynthesis, 7 circadian rhythm, 8 and tactic responses 9-12 using a unicellular motile green alga, Chlamydomonas reinhardtii, as a model organism of microalgae. Author to whom correspondence should be addressed.…”

“…Till date, the chemotactic responses in this microalga have been investigated using a limited number of chemicals, including ammonium (NH 4 þ ) ion. 8,10,12 Furthermore, the chemotaxis of C. reinhardtii to several chemicals (e.g., L-arginine and CoCl 2 ) is disputable. [10][11][12] Although HCO 3 À is an important inorganic carbon source in C. reinhardtii, it is not known that HCO 3 À triggers a chemotactic response of C. reinhardtii.…”