Symbiotic Chloroplasts; Their Photosynthetic Products and Contribution to Mucus Synthesis in Two Marine Slugs

The products of photosynthetic 14CO2 fixation by symbiotic chloroplasts in the marine sacoglossan opisthobranch gastropods Tridachia crispata (Mörch) and Tridachiella diomedea (Bergh) were compared with those of the siphonous green alga Caulerpa sertularioides. 2. After six hours photosynthesis in NaH14CO3, the distribution of 14C in organic compounds in the two slugs was similar, but different from that in the plant. 3. The major soluble 14C-labelled carbohydrates found were glucose and sucrose in the plant and glucose and galactose in the slugs. 4. The plant contained appreciable 14C-galactolipids, while little 14C could be detected in galactolipids in chloroplasts in the animals. In both slugs and alga large quantities of 14C were incorporated into polysaccharide. 5. After pulse-labelleing for one hour, 14C-galactose was the major soluble carbohydrate detected in Tridachia. Subsequently, the galactose decreased with a concomitant increase in 14C-glucose. Thereafter maximum 14C-glucose was detected in secreted 14C-mucus suggesting utilization of galactose and glucose in mucus synthesis. 6. It is estimated that the rate of turnover of 14C in the mucus-secreting pedal gland of Tridachia is 10-12 hours, suggesting that chloroplast products play an important role in animal mucus synthesis.