SYMBIOTIC CHLOROPLASTS; THEIR PHOTOSYNTHETIC PRODUCTS AND CONTRIBUTION TO MUCUS SYNTHESIS IN TWO MARINE SLUGS

¹ The Marine Laboratory, Discovery Bay, Jamaica; the Department of Agricultural Science, University of Oxford, England and the Zoology Department, University of California, Los Angeles, California 90024

1. 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.

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