A comparative study of photoadaptation in four diatoms isolated as endosymbionts from larger foraminifera |
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Authors: | M J Lee R Ellis J J Lee |
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Institution: | (1) Department of Biology, Bucknell University, 17837 Lewisburg, Pennsylvania, USA;(2) Department of Biology, City College of City University of New York, Convent Avenue at 138 th Street, 10031 New York, NY, USA |
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Abstract: | Four endosymbiotic diatoms were isolated from 2 species of larger foraminifera collected in the Red Sea and Hawaii. The photoadaptive responses of the cultured diatoms were measured at 312, 19 and 7 W cm-2. Two of the diatoms (Fragilaria shiloi and Nitzschia laevis), both isolated from Amphistegina lessonii, grew fastest at 312 W cm-2. The other two diatoms (N. valdestriata and N. panduriformis) which were isolated from Heterostegina depressa, grew best at 19 W cm-2. Of the four diatoms, F. shiloi grew best at high light levels. Also in F. shiloi, chlorophyll c content per cell was directly proportional to light intensity; in contrast chlorophyll a and carotenoids increased to maxima at 19 W cm-2. The chlorophyll a and c and carotenoid content of N. valdestriata were also maximal at 19 W cm-2. Photosynthetic rates, measured by respirometry, suggested that the diatoms were photoinhibited at higher light intensities and did well at moderately low light intensities (175W cm-2). The photocompensation points of all 4 diatoms were about 2% of the light available in the spring at 1-m depth at Elat on the Red Sea. At Elat the photocompensation point would lie between 40 and 50 m if the algae were free in nature. The amount of attenuation of light by the shells of the host has not yet been measured. Presumably photocompensation of the algae within hosts is reached at depths less than 40 m. |
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