RESPIRATION AND PHOTOSYNTHESIS IN CONVOLUTA ROSCOFFENSIS GRAFF, INFECTED WITH VARIOUS SYMBIONTS

¹ Haskins Laboratories, Yale University, 165 Prospect Street, New Haven, Connecticut 06520

Measurements of oxygen balance were made with a recording polarographic electrode on 3 strains of worms reinfected with several natural and unnatural symbionts.

1. The photosynthesis/respiration (P/R) ratios and net photosynthesis varied with light intensity but were independent of worm strains or algal species: compensation light intensities were also similar.

2. However, the content in chlorophyll a/mm³ of worm varied and in worms reinfected with unnatural symbionts was - that found in natural symbiont reinfected worm. Consequently, worms with unnatural symbionts produced more O₂/µg chlorophyll a.

3. Cell size of different species of symbiont varied but average chl. a/cell was similar. Observations in vivo and with thick and thin EM sections showed that the number of symbionts/mm³ worm varied with symbiont species. Natural symbionts were more numerous, and more densely packed in superimposed tiers, mutual shading may be responsible for a less efficient photosynthesis.

4. However, adaptation to laboratory light intensities and the assumption implicit in the measurements and calculations of the P/R that dark respiration is equal to photorespiration may also account for the uniformity of results with different symbionts.

5. The P/R ratios appear to be an insensitive way to distinguish obligatory from faculitative symbionts. At best, positive P/R ratios indicate that excess photosynthate is produced but it does not indicate whether or not the photosynthate is released, taken up and/or utilized by the host, nor its nutritional contribution.