Paralytic shellfish toxins (PSTs) are a group of potent neurotoxic alkaloids produced by cyanobacteria and dinoflagellates.Accumulations of PST can induce mass death of fish,high mortalities of marine mammals and human paralytic shellfish poisonings (PSPs),which has become a threat to marine aquaculture and shellfish consumers due to the global increase of PST-producing algal blooms.The PST biosynthesis pathway has been unveiled in cyanobacteria,yet little is known about dinoflagellates.Previously,the toxin biosynthesis was found coupling closely with the cell cycle in dinoflagellates.Here,the colchicine is used to arrest the cell cycles of a toxigenic dinoflagellate A.catenella (ACHK-T) and its non-toxic mutant (ACHK-NT),and their protein profiles were compared with the control groups respectively using iTRAQ-based proteomic approach.Flow cytometry and toxin analysis showed that the cell cycles were arrested in G1 phase in both of these two strains and PST production was inhibited in ACHK-T.Moreover,a total of 113 (ACHK-T) and 253 (ACHK-NT) proteins were differentially expressed among the 6988 identified proteins.Colchicine treatment triggered the reactive oxygen species scavenging and protein degradation in both of these two strains while the chlorophyll biosynthesis and nitrogen metabolism responding diversely between them.A feedback regulation mechanism should be functioned between PST production and nitrogen metabolism and it keeps the expressions of nitrate reductase and glutamine synthetase away from down-regulated in the colchicine-treated ACHK-T.In order to balance the cellular nitrogen metabolism,the colchicine-treated ACHK-T utilizes the nitrogen originally for PST biosynthesis to the enhanced chlorophyll biosynthesis process.Our study extended the understanding of the PST biosynthesis process in dinoflagellates and provided new insights for the tangled relationship between toxin production and nitrogen metabolism.