Ultraviolet screening by slug tissue and tight packing of plastids protect photosynthetic sea slugs from photoinhibition

AbstractOne of the main mysteries regarding photosynthetic sea slugs is how the slug plastids handle photoinhibition, the constant light-induced damage to Photosystem II of photosynthesis. Recovery from photoinhibition involves proteins encoded by both the nuclear and plastid genomes, and slugs with plastids isolated from the algal nucleus are therefore expected to be incapable of constantly repairing the damage as the plastids inside the slugs grow old. We studied photoinhibition-related properties of the sea slug Elysia timida that ingests its plastids from the green alga Acetabularia acetabulum. Spectral analysis of both the slugs and the algae revealed that there are two ways the slugs use to avoid major photoinhibition of their plastids. Firstly, highly photoinhibitory UV radiation is screened by the slug tissue or mucus before it reaches the plastids. Secondly, the slugs pack the plastids tightly in their thick bodies, and therefore plastids in the outer layers protect the inner ones from photoinhibition. Both properties are expected to greatly improve the longevity of the plastids inside the slugs, as the plastids do not need to repair excessive amounts of damage.

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Ultraviolet screening by slug tissue and tight packing of plastids protect photosynthetic sea slugs from photoinhibition

10.1101/2021.07.15.452583 ◽

2021 ◽

Author(s):

Vesa Havurinne ◽

Riina Aitokari ◽

Heta Mattila ◽

Ville Käpylä ◽

Esa Tyystjärvi

Keyword(s):

Photosystem Ii ◽

Uv Radiation ◽

Action Spectrum ◽

Light Response ◽

Sea Slug ◽

Acetabularia Acetabulum ◽

Sea Slugs

One of the main unsolved questions regarding photosynthetic sea slugs is how the slug plastids handle photoinhibition of Photosystem II. Photoinhibition has not been studied in detail in these animals although resilience against photoinhibition might obviously explain the longevity of plastids inside animal cytosol. Light response and action spectrum of photoinhibition were measured from the slug Elysia timida and its prey alga Acetabularia acetabulum. Plastid packing in the slugs and algae was compared with spectroscopic and microscopic methods. The importance of plastid concentration was also estimated by measuring photoinhibition from starved slugs. Compared to A. acetabulum, E. timida is highly resistant against photoinhibition. The resilience of the slugs is even more pronounced in the UV-region, as the slug tissue screens UV radiation. The plastids in the slug tissue are tightly packed, and the outer plastids protect the inner ones from photoinhibition. The sea slug E. timida protects its plastids from photoinhibition by screening UV radiation and packing the plastids tightly in its tissues. Both mechanisms enhance the longevity of the plastids in slug cytosol and ameliorate the need for repair of photoinhibited Photosystem II.

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Chloroplast Acclimation, Photodamage and Repair Reactions of Photosystem-II in the Model Green Alga Dunaliella salina

The Alga Dunaliella ◽

10.1201/b10300-12 ◽

2009 ◽

pp. 273-299 ◽

Cited By ~ 2

Author(s):

Kittisak Yokthongwattana ◽

EonSeon Jin ◽

Anastasios Melis

Keyword(s):

Photosystem Ii ◽

Green Alga ◽

Dunaliella Salina

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Pigment and Fatty Acid Heterogeneity in the Sea Slug Elysia crispata Is Not Shaped by Habitat Depth

Animals ◽

10.3390/ani11113157 ◽

2021 ◽

Vol 11 (11) ◽

pp. 3157

Author(s):

Xochitl Guadalupe Vital ◽

Felisa Rey ◽

Paulo Cartaxana ◽

Sónia Cruz ◽

Maria Rosário Domingues ◽

...

Keyword(s):

Fatty Acid ◽

Total Lipid ◽

Animal Cells ◽

Habitat Depth ◽

Sea Slug ◽

Chl A ◽

Sea Slugs ◽

Long Time ◽

Biochemical Condition

Long-term retention of functional chloroplasts in animal cells occurs only in sacoglossan sea slugs. Analysis of molecules related to the maintenance of these organelles can provide valuable information on this trait (kleptoplasty). The goal of our research was to characterize the pigment and fatty acid (FA) composition of the sea slug Elysia crispata and their associated chloroplasts that are kept functional for a long time, and to quantify total lipid, glycolipid and phospholipid contents, identifying differences between habitats: shallow (0–4 m) and deeper (8–12 m) waters. Specimens were sampled and analyzed after a month of food deprivation, through HPLC, GC-MS and colorimetric methods, to ensure an assessment of long-term kleptoplasty in relation to depth. Pigment signatures indicate that individuals retain chloroplasts from different macroalgal sources. FA classes, phospholipid and glycolipid contents displayed dissimilarities between depths. However, heterogeneities in pigment and FA profiles, as well as total lipid, glycolipid and phospholipid amounts in E. crispata were not related to habitat depth. The high content of chloroplast origin molecules, such as Chl a and glycolipids after a month of starvation, confirms that E. crispata retains chloroplasts in good biochemical condition. This characterization fills a knowledge gap of an animal model commonly employed to study kleptoplasty.

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