Changes in intracellular and extracellular free polyamines during the growth cycle of Prorocentrum donghaiense

We used HPLC to measure the concentrations of free putrescine, spermidine, and spermine in cells and culture medium during the growth of Prorocentrum donghaiense. Spermine was the main intracellular free polyamines in Prorocentrum donghaiense. The intracellular concentration of free polyamines kept increasing during the growth cycle and the ratio of spermine to putrescine increased with cell density. Changes in the ratios of spermine/spermidine in Prorocentrum donghaiense, however, occurred before changes in cell density, suggesting that polyamines can regulate cell growth and replication. Putrescine was the most abundant free polyamine in the culture medium, followed by spermine and spermidine. Changes to the media polyamines contents implied that Prorocentrum donghaiense could absorb free polyamines from the culture solution as well as release free polyamines into the medium during different growth periods, especially during the decline phase. These results suggest that masses of dead algae in the population decline phase would release abundant free polyamines into the environment.