Light-induced oxidative damage in yellow-green algae Vaucheria litorea

Abstract

Sea slug Elysia chlorotica incorporates chloroplasts of yellow-green algae Vaucheria litorea into its digestive tract cells where the chloroplasts remain active up to 9 months. The mechanism how these incorporated chloroplasts, which are referred to as kleptoplasts, remain active inside the sea slug cells is still unknown. The absence of protein transportation from cytosol should cause problems to photosynthesis as many of the ancestral chloroplasts genes have transferred to algal genome. The reason why these chloroplasts are particularly robust could be due to effective photoprotection mechanisms that decreases reactive oxygen species production in the thylakoid membranes of V. litorea.

Studying the light-induced damage in thylakoids of V. litorea in comparison to thylakoids of higher plant Spinacia oleracea provides insight to photosynthesis of V. litorea and could possibly reveal mechanisms involved in chloroplast longevity. In this study, light induced oxidative damage to proteins and lipids was measured using methods that enable detection of oxidized proteins and lipids. In addition, the ratio between the two photosystems in thylakoids was determined and chloroplast isolation method was tested for future projects.

The results from oxidative damage experiments show that during a high light treatment lipids and proteins of V. litorea are more prone to oxidative damage by reactive oxygen species than those of S. oleracea. The Photosystem II/Photosystem I stoichiometry study showed that V. litorea had very similar ratio of photosystems compared to S. oleracea, indicating that the comparison of these two species is justified. These results establish a backbone for further studies of photosynthesis in V. litorea.