Sexual life cycle of dinoflagellates could be induced by environmental stress such as limiting nutrient (nitrogen and/or phosphate limitation) and low temperature. However, the observed frequency of sexual reproduction is still very low. With the only diploid stage (2C DNA content) as a zygote, most of dinoflagllates are haploid (1C DNA content) throughout their vegetative life cycle. The heterotrophic dinoflagellates C. cohnii can be cultured to high density under laboratory condition and is the agent for the industrial production of omeaga-3 highly unsaturated fatty acids. C. cohnii is homothallic, which means that gametes can be formed and then fused to zygote within the same clonal culture. Previous studies based on genetic data extrapolate meiosis occurred in C.cohnii. There is n...[ Read more ]

Sexual life cycle of dinoflagellates could be induced by environmental stress such as limiting nutrient (nitrogen and/or phosphate limitation) and low temperature. However, the observed frequency of sexual reproduction is still very low. With the only diploid stage (2C DNA content) as a zygote, most of dinoflagllates are haploid (1C DNA content) throughout their vegetative life cycle. The heterotrophic dinoflagellates C. cohnii can be cultured to high density under laboratory condition and is the agent for the industrial production of omeaga-3 highly unsaturated fatty acids. C. cohnii is homothallic, which means that gametes can be formed and then fused to zygote within the same clonal culture. Previous studies based on genetic data extrapolate meiosis occurred in C.cohnii. There is no prior analysis of C. cohnii regarding sexual induction conditions.

C. cohnii strains have been found in tropical/subtropical region and cell proliferation rate decreased with reducing temperature from 28°C to 15°C. In present study, we investigated the effect of nutrient depletion (phosphate or nitrogen depletion), solid substrate and low temperature on sexual reproduction rate of C. cohnii. The optimum conditions for increasing the frequency of sexual reproduction were reported. This would allow the investigation of meiosis at biochemical and molecular level in order to produce synchronized meiotic populations. The actin inhibitor cytochalasin D and light-dark cycle treatment were also tested for the ability to postpone non-mitotic cell division of sexual reproduction. Transcript level of sexual reproduction specific gene Hap2, DMC1, MND1 was increased at low temperature, which further indicated that C. cohnii were undergoing sexual reproduction under these conditions.