PARENT SESSION
Posters P3B Photosynthetic acclimation: Ecophysiology, diverse environments. Abstracts (479-522)

Halophilic photosynthetic responses in the marine diatom Phaeodactylum tricornutum. Yuji Tanaka^*,1, Yusuke Matsuda¹, ¹ Department of Bioscience, School of Science and Engineering, Kwansei-Gakuin University, 2-1 Gakuen, Sanda, Hyogo, Japan

ABSTRACT- Physiological and biochemical responses of the marine diatom Phaeodactylum tricornutum to various salt conditions were investigated. Cells of the marine diatom P. tricornutum grown in f/2 enriched artificial seawater (F2ASW) containing 0.5 M NaCl were transferred to manipulated [NaCl] and cultured at 20 °C for 2 weeks under continuous illumination. Cells were grown well under 0.1 M to 1.0 M NaCl. Partial deprivation of Cl^- by replacement of NaCl with Na₂SO₄ under constant [Na⁺] of 1.0 M also exhibited little inhibitory effect on growth whereas the addition of 0.2 M LiCl, 0.2 M KCl, 1.0 M Sorbitol, or 0.9 M Cholinechloride to the F2ASW containing 0.1 M NaCl drastically inhibited growth. These inhibitory effects with probably Cl^-, osmotic and cationic stresses were reduced by the addition of Na₂SO₄ in a concentration dependent manner. Under above-described stressed conditions, activities of the linear electron transport and PSII were measured with oxygen evolution rate respectively under the absence and the presence of 1,4-p-benzoqinon. All these activities were stimulated upon the addition of 0.45 M Na₂SO₄ to the modified F2ASW containing 0.1 M NaCl, whereas these were inhibited upon the addition of 0.9 M cholinechloride. The addition of 0.2 M LiCl, 0.2 M KCl, or 1.0 M sorbitol exhibited little effect on photosystem. The results of Fv/Fm measurement also agreed well with these data. Given these results, unlike previous studies on phtosystems, Cl^- possesses a toxic effect on PSII and Na⁺ may protect PSII in the marine diatom P. ricornutum. Na⁺ was also shown to reduce osmotic and cationic stresses. These observations suggested a possible occurrence of novel halophilic systems in marine photoautotrophs.

KEY WORDS: salt, diatom, PSII