In vivo and in vitro differences in chloroplast functionality in the two north Atlantic sacoglossans (Gastropoda, Opisthobranchia) Placida dendritica and Elysia viridis
- 319 Downloads
The photosynthetic functionality in chloroplasts in the two sacoglossan molluscs Placida dendritica and Elysia viridis from the Trondheim fjord in Norway was studied. P. dendritica and E. viridis with no functional chloroplasts in their digestive system were introduced to the green macroalgae Codium fragile. Our results showed that P. dendritica was not able to retain functional (photosynthetic) chloroplasts. Transmission electron microscopy (TEM) showed that chloroplasts were directly digested when phagocytosed into the digestive cells. Four stages of chloroplast degradation were observed. A corresponding operational quantum yield of chl a fluorescence (ΦPSII ~ 0) indicated autofluorescence, and the presence of highly degraded chl a supported these observations. In contrast, E. viridis was able to retain functional chloroplasts. For this species it took only 1 week for the chloroplasts inside the digestive cells to acquire the same ΦPSII and light utilisation coefficient (α) as C. fragile kept under the same light conditions. Data for 8 days showed a 2–6-fold increase in the maximum photosynthetic rate (Pmax) and light saturation index (Ek) relative to C. fragile. This increase in available light was probably caused by a reduced package effect in the digestive gland of E. viridis relative to C. fragile, resulting in a partial photoacclimation response by reducing the turnover time of electrons (τ). Isolated pigments from C. fragile compared to E. viridis showed the same levels of photosynthetic pigments (chl a and b, neoxanthin, violaxanthin, siphonaxanthin, siphonein and β,ε-carotene) relative to μg chl a (w:w), indicating that the chloroplasts in E. viridis did not synthesise any new pigments. After 73 days of starvation, it was estimated that chloroplasts in E. viridis were able to stay photosynthetic 5–9 months relative to the size of the slugs, corresponding to an RFC of level 8 (a retention ability to retain functional chloroplasts (RFC) for more than 3 months). The reduction in ΦPSII, Pmax and α as a function of time was caused by a reduction in chloroplast health and number (chloroplast thylakoid membranes and PSII are degraded). These observations therefore conclude that chloroplasts from C. fragile cannot divide or synthesise new pigments when retained by E. viridis, but are able to partially photoacclimate by decreasing τ as a response to more light. This study also points to the importance of siphonaxanthin and siphonein as chemotaxonomic markers for the identification of algal sources of functional chloroplasts.
KeywordsThylakoid Membrane Digestive Gland Digestive Cell Chloroplast Division Green Macroalgae
We would like to thank Torkild Bakken and Anita Kaltenborn for field assistance collecting sacoglossans and algae, Heike Wägele and Ingo Burghardt for assistance with the light microscopy sections at Spezielle Zoologie, Ruhr-Universität Bochum, Germany, and Kåre Tvedt and Linh Huoang at the Department of Laboratory Medicine, NTNU, for practical assistance with the TEM sections, and Kjersti Andresen at Trondhjem Biological Station, for HPLC pigment isolation. This study was supported by the Norwegian Research Council to J. Evertsen (NFR 153790/120). All experiments comply with the current laws of the country in which the experiments were performed.
- Burghardt I, Evertsen J, Johnsen G, Wägele H (2005) Solar powered seaslugs: mutualistic symbiosis of aeolid Nudibranchia (Mollusca, Gastropoda, Opisthobranchia) with Symbiodinium. Symbiosis 38:227–250Google Scholar
- Clark KB, Jensen KR, Stirts HM (1990) Survey for functional kleptoplasty among west Atlantic Ascoglossa (=Sacoglossa) (Mollusca: Opisthobrachia). Veliger 33(4):339–345Google Scholar
- Green BJ, Li W-Y, Manhart JR, Fox TC, Summer EL, Kennedy RA, Pierce SK, Rumpho ME (2000) Mollusc–algal chloroplast endosymbiosis: photosynthesis, thylakoid protein maintenance, and chloroplast gene expression continue for many months in the absence of the algal nucleus. Plant Physiol 124:331–342CrossRefGoogle Scholar
- Greene RW, Muscatine L (1972) Symbiosis in sacoglossan opisthobranchs: photosynthetic products of animal–chloroplast associations. Mar Biol 14:253–259Google Scholar
- Grzymbowski Y, Stemmer K, Wägele H (2007) On a new Ercolania Trinchese, 1872 (Opisthobranchia, Sacoglossa, Limapontiidae) living within Boergesenia Feldmann, 1950 (Cladophorales), with notes on anatomy, histology and biology. Zootaxa 1577:3–16Google Scholar
- Hinde R (1980) Chloroplast ‘‘symbiosis’’ in sacoglossans molluscs. In: Schwemmler W, Schenk HEA (eds) Endocytobiology, endosymbiosis and cell biology. Proceedings of the international colloquium on endosymbiosis and cell research, Tubingen, Germany, Walter de Gruyter, pp 729–736Google Scholar
- Jeffrey SW, Mantoura RFC, Bjørnland T (1997) Data for the identification of 47 key phytoplankton pigments. In: Jeffrey SW, Mantoura RFC, Wright SW (eds) Phytoplankton pigments in oceanography: guidelines to modern methods. UNESCO, Paris, pp 449–559Google Scholar
- Jensen KR (1980) A review of sacoglossan diets, with comparative notes on radular and buccal anatomy. Mal Rev 15:55–77Google Scholar
- Trench RK (1980) Uptake, retention and function of chloroplasts in animal cells. In: Schwemmler W, Schenk HEA (eds) Endocytobiology, endosymbiosis and cell biology. Proceedings of the international colloquium on endosymbiosis and cell research. Tubingen, Germany, Walter de Gruyter, pp 703–727Google Scholar
- Webb WL, Newton M, Starr D (1974) Carbon dioxide exchange of Alnus rubra: a mathematical model. Ecologia 17:281–291Google Scholar
- Yokohama Y (1981) Distribution of the green light-absorbing pigments siphonaxanthin and siphonein in marine green algae. Bot Mar 24:637–640Google Scholar