Excretion from the marine diatom Chaetoceros affinis was investigated in batch cultures. The rates of release of carbohydrates and amino acids per cell were higher in rapidly growing cells than in stationary phase cells. However, because photosynthesis per cell decreased significantly during nutrient depletion, excretion constituted 58% of total photosynthesis in stationary cells compared to 10% during exponential growth. The most prominent extracellular amino acids in the exponential phase were aspartic acid, glutamic acid, serine, glutamine, glycine, alanine, valine and leucine. In the stationary phase arginine, asparagine, tyrosine and isoleucine were also produced. Carbohydrate, of which polysaccharide constituted >80%, was the most abundant extracellular component released.
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Myklestad et al. (1989) studied this question.