How do eyeless corals see light?
Akihisa Terakita, professor in the Graduate School of Science at Osaka Metropolitan University, dives in to find out more.
Akihisa Terakita and Mitsumasa Koyanagi are Professors at Osaka Metropolitan University’s Graduate School of Science with interest in photoreception.
Professor Mitsumasa Koyanagi and myself were lead authors for a study of light-sensing proteins, opsins, in corals. We obtained new insights into how corals and their symbiotic light-sensitive algae interact.
Most animals use retinal to absorb light, which forms a chemical bond with opsin, known as a Schiff base. Whether this bond carries a positive charge determines if the opsin absorbs visible light or UV. For visible light absorption, the positive charge is stabilized by negatively charged amino acids. However, reef-building corals lack these amino acids.
Our team found that Acropora tenuis corals use chloride ions from the environment instead. This suggests an association between environmental pH and light absorption. Under low pH conditions, the amount of positively charged particles increases, promoting the formation of positively charged Schiff bases and favoring visible-light detection. High pH means the opposite, favoring UV light.
This pH-dependent relationship is important for the coral’s partnership with algae. As the algae perform photosynthesis, carbon dioxide is consumed, raising the pH, which in turn, regulates the coral’s light sensing.
It’s a fascinating example of how symbiosis works in the complex reef ecosystem.
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[Osaka Metropolitan University - Research News] - How eye-less corals see the light
