ECOPHYSIOLOGICAL CHARACTERIZATION OF 2 LIFE FORMS, RESTING SPORES AND RESTING CELLS, OF A MARINE PLANKTONIC DIATOM, CHAETOCEROS PSEUDOCURVISETUS, FORMED UNDER NUTRIENT DEPLETION

Ecophysiological characteristics of 2 life forms, resting spores and resting cells, produced from vegetative cells of the marine diatom Chaetoceros pseudocurvisetus (Mangin) under nitrogen depletion were investigated. Carbon and silicon were concentrated in resting spores to a greater extent than nitrogen and chlorophyll a (chi a) although the levels of nitrogen and chi a were similar to those in vegetative cells. Resting cells were similar in appearance to vegetative cells but with weakly pigmented, shrunken and fragmented chloroplasts, and contained slightly more silicon, reduced nitrogen and chl a and similar amounts of carbon in comparison with the vegetative cells. Respiratory and photosynthetic activity was depressed in both resting spores and resting cells. Net photosynthesis was slightly positive in resting spores and slightly negative in resting cells. Both resting spores and resting cells accumulated neutral lipids mainly composed of myristic (C-14.0), palmitic (C-16.0) and palmitoleic (C-16.1) acids as a stored energy source with increased unsaturation of fatty acids. Resting spores also stored large amounts of glucose in reserved polysaccharides. These characteristics indicate that each life form represents a different degree of the adaptive resting stage for survival under nutrient depletion.