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The relationship between O2 and an active oxygen scavenging system in Chlorella vulgaris var.vulgaris (IAM C-534) was investigated. When Chlorella vulgaris was exposed to 2% O2, only traces of active oxygen scavenging enzymes were found. When the Chlorella vulgaris was treated with 20% or 50% O2, it was shown that the level of enzyme activity increased as the O2 concentration increased. An increase in enzyme activity was not found in any specific enzyme but in all of the enzymes, but the level of glutathione and ascorbate remained the same in all the cases. In addition, the photosynthetic efficiency also decreased as the concentration of O2 was increased. These results suggest that an O2 enriched environment can lead to an increase in the production of active oxygen species such as O2.- and H2O2 and to a decrease in the photosynthetic efficiency in Chlorella vulgaris. The hydroxyl radical (.OH) was detected directly in the Chlorella vulgaris suspension with a spin trapping reagent. It was also clear that the increase in the .OH intensity as the visible light intensity increased was unrelated to the O2 concentration. It was suggested that the conditions for producting .OH and the other active oxygen species were different, and that two types of oxygen stress should exist in the Chlorella vulgaris.

Using ESR with 5,5-dimethyl-1-pyrroline N-oxide (DMPO) as a spin-trapping reagent, we measured the levels of free radical species generated from living cells of Chlorella vulgaris var. vulgails (IAM C-534). To investigate the production of free radicals in the living Chlorella vulgaris cells, the influence of DMPO toward the intact cells of the Chlorella vulgaris using the O2 evolution rate was first studied as a guide. Since the O2 evolution rate was not changed by DMPO, it was judged that DMPO has no toxicity toward the intact cells of Chlorella vulgaris. Only hydroxyl radicals (.OH) were detected as the DMPO-OH adduct in the suspension of intact cells of Chlorella vulgaris irradiated with visible light. Moreover, since production of .OH was inhibited by some hydroxyl radical scavengers such as KI and ethanol, production of .OH was proved to be due to hydroxyl radicals. It was also clear that the intensity of .OH increased with increasing irradiation intensity of visible light. Therefore, it was suggested that .OH might be one of the photoinhibition factors of the intact Chlorella vulgaris cells in severe light conditions.

Sterile Ulva, which is a macroalga, has the potential to grow stably; therefore, this seaweed is expected to be an efficient resource of functional food containing various nutrients such as sulfur amino acids, proteins, carbohydrates, and minerals. Ulva latuca was selected from the "Marine Park" in Tokyo Bay, and its growth rate (g-dry/[m2.d]) was measured using model reactors located on the land or on the surface of the sea at Yokohama. The growth rate of U. lactuca was recorded to be approx 20 g-dry/(m2.d), which is estimated to be 10 times greater than that in a natural field in the Marine Park. In addition, this growth rate was higher than that of conventional crops such as corn and rice on a farm or paddy. These data led us to newly design and propose a floating type of labor-efficient U. lactuca production system. d-Cysteinolic acid, which is included in U. lactuca as a major sulfur amino acid, inhibited the Fenton reaction, resulting in suppression of hydroxyl radical production and singlet oxygen. Addition of the sulfur amino acid (1 microM) to HepG2 cells markedly decreased the intracellular triglyceride level. Hence, this proposed facility also has the potential for industrial production of a valuable resource for the primary prevention of lifestyle-related diseases using enriched or eutrophied seawater.