• chloroplasts
• Elysia
• ETR
• Fluorescence
• kleptoplasty
• light curves
• photoprotection
• photosynthesis
• pigments
• xanthophyll

Sacoglossa sea slugs feed on algae and maintained chloroplasts photosynthetically active inside their body. Photosynthetic organisms have evolved different ways to protect photosystem I and II (PSI and PSII respectively) from photodamage like adjusting light absorption, and the non-photochemical quenching (NPQ) processes but chloroplastic genome can encode only a small part of the proteins and pigments necessary for the protection against light stress (Edrhard et al. 2008). NPQ is related to the xantophyll cycle (XC): a reversible interconversion of zeaxanthin (Z) and violaxanthin (V) thank to the enzyme violaxanthin deepoxidase that converts violaxanthin to zeaxanthin (via antheraxanthin, A) and increases the depoxidation state of the XC pool. The zeaxanthin epoxidase catalyzes the reverse reaction. This work is divided into three parts. In the first experiment, Fv/Fm ratio (potential photochemical PSII efficiency) and rapid light curves (RLCs) were calculated in E. viridis and P. dendritica. The same was realised in E. timida and A. acetabulum. The Fv/Fm ratio and the RLCs remained constant regardless of the starvation period and of the morphotype except in P. dendritica. The second experiment was an analysis of the host-mediated photoprotection; B. hypnoides and of C. tomentosum were cultured under Low light (LL; 20 µmol of photons m-2 s-1) and High light (HL; 200 µmol of photons m-2 s-1). When the light curves showed a photoacclimation the animals were fed with the two algae The area of the dorsal surface of specimens of E. viridis and E. timida was measured via software after a fixed time of exposure to light before and after the feeding. Results suggested an influence of the acclimation light on the host-mediated photoprotection. The pigment composition of the animals and the algae was then analysed via HPLC. The pigment profile was maintained after one week of starvation in all the specimens except P. dendritica confirming the ability for a kleptoplastic animal not to digest the plastids immediately. An unknown carotenoid spotted only in E. viridis and E. timida could probably be implied to stabilize the chloroplast inside the animal cell. A build-up of the pigment trans-neoxanthin, that usually protect the LHCII from light, was observed in the HL acclimated organisms. An analysis of E. viridis treated with a Light-Stress-Recovery (LSR) allowed to identify this process as a long-term photoacclimation mechanism. The xantophyll cycle was analysed via HPLC in specimens of A. acetabulum and E. timida undergone the LSR protocol. The de-epoxidation state of the cycle [(A + Z)/(V + A + Z)] showed a normal cycle in the algal sample and in the fed slug while in the starved animals was reported an inability to reconvert Z to V probably related to an excessive damage of the chloroplast, so unable to influence the gene expression. This work provides a series of starting point to proceed with a deeper analysis, relying also on molecular tools. These knowledges, opportunely integrated, would be a great support for all the engineering project involved into artificial photosynthesis.