Kiyoshi Sugata

Detection of Hydroxyl Radical in Intact Cells of 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.

Effect of hydroxyl radical on intact microalgal photosynthesis

Abstract Photosynthetic CO 2 fixation with microalgae for new energy and chemical sources is one of the potential method to mitigate CO 2 emission. To gain the more productivities for CO 2 mitigation, the enhancement of photosynthetic productivity is required. We focused on the active oxygen that is supposed to be produced in algal cells and causes harmful effects on photosynthesis under high irradiation that is the case of outdoor cultivation circumstances. In this report, we have challenged to detect the active oxygens in microalgal cells, and then the results were described. The levels of free radical species generated in the living cells of Chlorella vulgaris var. vulgaris (IAM C-534) were detected with electron spin resonance (ESR) spectrometer with 5,5 dimethyl-1-pyrroline N-oxide (DMPO) as a spin-trapping reagent. Before detecting the free radicals in the living Chlorella cells, the influence of DMPO concentration toward the photosynthetic growth rate of the cells was measured. Since the growth rate was not influenced by up to 130 mM DMPO, the DMPO concentration was adjusted to 90 mM during the measurement. Only one DMPO adduct, which is assigned as the hydroxyl radical (DMPO-OH; aN=1.49mT, aH=1.49mT) was detected in the solution of intact cells of Chlorella vulgaris irradiated with visible light (1). Moreover, the production of DMPO-OH adducts was inhibited by some hydroxyl radical ( − OH) scavengers such as KI and ethanol. It has been estimated that − OH is one of the photoinhibition factors of the photosynthetic organisms. But, − OH has never been detected in vivo. In this report, − OH was detected in vivo, and the − OH was increased according to the light intensity.

Evaluation of Active Oxygen Effect on Photosynthesis of Chlorella vulgaris

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.