Effects of 3-(3,4-Dichlorophenyl)-1,1-Dimethylurea on the Cell Cycle in Euglena gracilis

Abstract

The cell cycle of the photosynthetic unicellular alga Euglena gracilis growing in phototrophic medium is regulated by light. To investigate the relationship of this cell cycle response to light stimulated photosynthesis, we have tested the effect of the photosynthesis inhibitor 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) on Euglena cell cycle transit. While DCMU does not block light stimulated cells from entering the S phase of the cell cycle, it does inhibit the transit through G2/M. Triazine herbicides such as DCMU and atrazine have been shown to interrupt photosynthetic electron transfer at the PSII reaction center (6). The specificity of this inhibitor for photosynthesis has been demonstrated both biochemically as well as genetically. Binding studies using labeled atrazine have shown that the herbicides bind specifically to the DI polypeptide of the reaction center core complex (16). Furthermore, a mutant strain of Euglena has been isolated that is resistant to the effects of DCMU on its photosynthetic apparatus (12).The psbA gene encoding the DI protein has been sequenced from this strain (1 1), and has been shown to contain the same single base change found in the DCMU-resistant Chlamydomonas reinhardtii strain DCMU4 (6). The existence of these DCMU-resistant strains of algae and the studies associating resistance to a mutation in a component ofthe photosynthetic reaction center suggested that DCMU's effect on the cell cycle in DCMU-sensitive strains was directly attributable to its effect on photosynthetic electron transport. DCMU has, however, been shown to have many effects on cell metabolism aside from photosynthetic electron transport. Growth of Euglena in phototrophic medium in the presence of DCMU results in a reduction in the number ofchloroplasts per cell and structural changes in the remaining chloroplasts (21). Addition of DCMU to dark-grown resting Euglena exposed to light results in a decrease in ribulose bisphosphate carboxylase (RuBisco) activity (17). Removal of DCMU results in an increase in RuBisco activity even when chloroplast or cytoplasmic translation is inhibited. DCMU also partially inhibits the accumulation ofseveral chloroplast-encoded polypeptides in Euglena including the large subunit of RuBisco (13). The effects of DCMU on nuclear functions has not been well documented.We have found that DCMU at concentrations in the medium used to inhibit photosynthesis causes a decrease in the rate of transit through G2/M, but does not alter the efficiency with which light induced cells to enter the S phase of the cell cycle from Go. (23). Dark-grown Euglena were obtained by inoculating cells from a light-grown, phototrophic culture into organotrophic medium and allowing the culture to grow 10 d in a foil-wrapped flask. Two bleached strains of E. gracillis var bacillaris, W3BUL and W3BSmL, were obtained from Prof. Jerome Schiff, Brandeis University.Samples were prepared and analyzed on the flow cytometer by pelleting at 8000 rpm in an SM24 rotor (Sorvall) for 5 min, followed by tw...

Predicting the phytotoxic mechanism of action of LiCoO2 nanomaterials using a novel multiplexed algal cytological imaging (MACI) assay and machine learning

“…8 In this case, it may be possible that LCO had an impact on nuclear/cellular division through the impairment of photosynthetic electron transport. 53 These results are similar to that of DCMU treated cells, which, on average, had been reported to have significantly less nuclei/cell when compared to non-treated control cells, and had appeared to have inhibited nuclear division. 9 This would also be consistent with other photosynthetic organisms, like Euglena gracilis , in which similar impacts have been reported under impaired photosynthetic electron transport.…”

“…9 This would also be consistent with other photosynthetic organisms, like Euglena gracilis , in which similar impacts have been reported under impaired photosynthetic electron transport. 53…”

Novel Findings Regarding Photoinduced Commitments of G1-, S- and G2-phase Cells to Cell-cycle Transitions in Darkness and Dark-induced G1-, S- and G2-phase Arrests in Euglena¶

“…They were washed twice with saline buffer (3 mM Na 2 HPO 4 , 3 mM KH 2 PO 4 , 0.27 M NaCl, 10 mM KCl, pH 7.5) and then treated with ribonuclease A (100 g/mL) for 60 min at 37ЊC. Immediately before the FCM, they were stained with PI (40 g/mL) (3,7). The cell suspension was then filtered through Nytex screens (50 m pores) and analyzed with FACS .…”

“…The cell-division cycle in the photosynthetic algae Chlamydomonas and Euglena is thought to be made up of two consecutive processes: a precommitment stage and a commitment stage (1)(2)(3)(4)(5). Progression through the precommitment stage in cell-cycle phase G1 is dependent on photosynthetic growth.…”

Regulatory Functions of Cellular Energy Sensor SNF1-Related Kinase1 for Leaf Senescence Delay through ETHYLENE- INSENSITIVE3 Repression

“…Here we showed that DCMU treatment slows down senescence-associated chlorophyll degradation in detached leaves in the absence and presence of light. DCMU function in the dark was previously reported with regards to cell cycle regulation in a photosynthetic unicellular organism Euglena 38 . Furthermore, the regulatory mechanism of DCMU under light that blocks the early step of electron transport chain at PSII instructs that the more greening by DCMU treatment does not signify the more photosynthetically functional chloroplasts.…”