Blue Light Regulation of Cell Division in Chlamydomonas reinhardtii

Abstract

A delay in cell division was observed when synchronized cultures of the unicellular green alga Chiamydomonas reinhardtii growing under heterotrophic conditions were exposed to white light during the second half of the growth period. This effect was also observed when photosynthesis was blocked by addition of the photosystem 11 inhibitor 3-(3,4-dichlorophenyl)-1,1-dimethylurea. Light pulses of 10 minutes were sufficient to induce a delay in cell division in the presence or absence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea. A delay in cell division was induced by blue light but not by illumination with red or far-red light. The equal intensity action spectrum revealed two peaks at 400 and 500 nm.Photoautotrophically growing cultures of unicellular green algae can be synchronized by alternating periods of light and darkness (18,20,23). In the case of Chlamydomonas reinhardtii, synchronization by light/dark cycling was also achieved in the presence of acetate (8,26), which is metabolized by this phytoflagellate. C reinhardtii cultures synchronized in the presence of acetate continue to divide synchronously for one cell cycle period when transferred to heterotrophic growth conditions (26). This finding enabled us to investigate the differential effects of light on cell growth and cell division. Illumination at the beginning of the growth period caused an increased growth rate. As a consequence, the cells entered the division phase earlier than dark-grown cells (26). However, when the cultures were exposed to light after the cells had doubled their mass, a considerable delay in cell division was observed, which was accompanied by an extended growth period (26). The light-induced delay in cell division was also observed in the presence of DCMU, an inhibitor of PSII.These observations indicate that the transition from cell growth to cell division is regulated by a light/dark-responsive cell cycle switch in C. reinhardtii (26) and that photosynthesis is apparently not involved in this process. Therefore, we have investigated which wavelengths and intensities of light are effective in inducing a delay in cell division. The aim of these 'Supported by a grant (Vo 327/1) from the Deutsche Forschungsgemeinschaft.

Chloroplast division is regulated by the circadian expression ofFTSZandMINgenes inChlamydomonas reinhardtii

“…A delay in cell division was observed when synchronized cultures of C. reinhardtii growing under heterotrophic conditions in the dark were exposed to white light, during the second half of the growth period (Munzner & Voigt, 1992). Therefore, continuous light stimuli might disturb and reset the circadian clock, resulting in dampening of the rhythm.…”

Photobioreactors in Life Support Systems

“…Several hints in the literature suggest that blue light has an impact on cell division. Münzner and Voigt [61] described in 1992 that blue light (no specific wavelength mentioned) induced a delay in cell division in C. reinhardtii wildtype cultures (137C mt + ) compared to cultures grown with red and far-red light. Moreover, white light, with which formerly heterotrophically grown cells were illuminated, also caused that effect.…”

Cell Growth Control in an Algal Model

“…Interestingly, attainment of commitment can also be modulated by light properties. Blue light delays the attainment of commitment leading to a larger cell size at commitment followed by a delay in the cell division and division into more cells (Munzner and Voigt 1992;Oldenhof et al 2004aOldenhof et al ,b, 2006, while under red light cells attain commitment faster and divide sooner into fewer cells (Oldenhof et al 2004a(Oldenhof et al ,b, 2006. The attainment of commitment point/s and cell division probably involves active CDKs because CDK activity is correlated with the increase in the amount of p34 protein and its phosphorylation (John et al 1989) and also with the increase in CDK-like histone H1 kinase activity (Zachleder et al 1997).…”