培養条件下における浮遊性珪藻Ｃｈａｅｔｏｃｅｒｏｓ ｄｉｄｙｍｕｓ ｖａｒ． ｐｒｏｔｕｂｅｒａｎｓの休眠胞子形成と発芽

Abstract

Resting spore formation and germination were investigated using a clonal culture of Chaetoceros didymus var. protuberans (LAUDER) GRAN & YENDO under laboratory conditions. The effects of nutrient depletion (N or P) and darkness were studied on resting spore formation. Ch. didymus cells were grown at a temperature of 22°C deg;, under a light intensity of 160μmol m-2 s-1 using cool white lamps with a photo-cycle of 14hL-10hD. Three types of modified medium, i.e. nutrient-repleted (SWM-3: 2mM NO3-N, 0.1mM PO4-P), phosphate-limited (2mM NO3-N, 1.25μM PO4-P), and nitrate-limited (25μM NO3-N, 0.1mM PO4-P), were used for the experiment. Resting spores were observed only in N-limited cultures, while formed resting spores were much more frequently observed in N-limited cultures which were transferred to the dark at the onset of the stationary phase. Newly formed resting spores were stored in the dark at 22°C. After 8-day storage, the spores did not germinate under adequate conditions for germination (22°C, 160μmol m-2 s-1 with 14hL-10hD phote-cycle). After 13-day storage, the spores germinated within 1-2 days under the same conditions. Resting spores of Ch. didymus var. protuberans seem to have a short period (8-13 days) of mandatory dormancy during which the spores will not germinate. The results obtained in this study suggest that N-limitation was necessary to trigger resting spore formation, and that darkness was essential for resting spore maturation (acquisition of germinability).