Plant Physiol, April 2003, Vol. 131, pp. 1681-1691

Cellulose Synthesis Is Coupled to Cell Cycle Progression at G₁ in the Dinoflagellate Crypthecodinium cohnii

Department of Biology, Hong Kong University of Science and Technology, Clearwater Bay, Kowloon, Hong Kong SAR, People's Republic of China

Cellulosic deposition in alveolar vesicles forms the "internal cell wall" in thecated dinoflagellates. The availability of synchronized single cells, the lack of secondary deposition, and the absence of cellulosic cell plates at division facilitate investigation of the possible roles of cellulose synthesis (CS) in the entire cell cycle. Flow cytograms of cellulosic contents revealed a stepwise process of CS in the dinoflagellate cell cycle, with the highest rate occurring at G₁. A cell cycle delay in G₁, but not G₂/M, was observed after inhibition of CS. A cell cycle inhibitor of G₁/S, but not G₂/M, was able to delay cell cycle progression with a corresponding reduction of CS. The increase of cellulose content in the cell cycle corresponded well to the expected increase of surface area. No differences were observed in the cellulose to surface area ratio between normal and fast-growing G₁ cells, implicating the significance of surface area in linking CS to the coupling of cell growth with cell cycle progression. The coupling of CS to G₁ implicates a novel link between CS and cell cycle control, and we postulate that the coupling mechanism might integrate cell wall integrity to the cell size checkpoint.