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CHANGES IN CHLOROPHYLL A FLOURESCENCE AND PIGMENT RATIOS DURING DIFFERENT GROWTH PHASES OF A UNICELLULAR MARINE CHAETOCEROS (BACILLAROPHYCEAE) IN BATCH CULTURE
Citation:
Thursby, G B., A. F. Santos, AND A. Sigleo. CHANGES IN CHLOROPHYLL A FLOURESCENCE AND PIGMENT RATIOS DURING DIFFERENT GROWTH PHASES OF A UNICELLULAR MARINE CHAETOCEROS (BACILLAROPHYCEAE) IN BATCH CULTURE. Presented at U. of New Hampshire Northeast Algal Symposium, Durham, NH, April 19-21, 2002.
Description:
Interpretations of chlorophyll a fluorescence data are based largely on application with green algae and higher plants. This study evaluated the interpretation of fluorescence data for a unicellular marine diatom. Chaetoceros sp. was grown in 4-liter batch cultures on a 16:8, L:D cycle under 200 E m-2 s-1 of cool-white fluorescence light using medium f and 30 ppt natural seawater. Cultures were aerated to maintain cells in suspension and minimize inorganic carbon limitation. Cell number (haemocytometer?at end of dark cycle), pigment concentrations (HPLC?3 hours into light cycle), and chlorophyll a fluorescence induction (Plant Efficiency Analyzer?at end of dark cycle) were monitored for 38 days, following cells through log-phase and senescent-phase growth. Cell numbers increased steadily until around day 20 or 22 (depending on the culture), then began a steady decline, with little or no time in stationary-phase. An analysis of the fluorescence data suggested that the number of active Photosystem II reaction centers per cell decreased as the cultures began to decline. The degree of inactivation increased daily as the cell numbers continued to decrease. The concentration of chlorophyll a per cell and the ratio of the major accessory pigments to chlorophyll a (e.g., fucoxanthin, chlorophyll C1 + C2) remained relatively constant throughout the experiment. The ratio of chlorophyll C1 to chlorophyll C2, however, began to increase at about the time the cultures were senescing (ca. day 20). In addition, the sum of the xanthophylls diatoxanthin and diadinoxanthin per cell decreased during the course of the culture cycle and a xanthophyll tentatively identified as zeaxanthin unexpectedly appeared at the time the cell numbers were declining, and continued to increase until the end of the experiment. The basic interpretation of fluorescence induction kinetics for diatoms appeared to be similar to that for green plants, however, there were differences in the diatom response beyond the initial induction phase.