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A research by University of Southampton has discovered a mechanism as to how corals use their pink and purple colors as sunscreen to shield them against damaging sunlight. Many reef corals are found to flourish in sunlight as their light dependent symbiotic algae produce sugars and lipids. However in shallow water where sunlight reaches in more than required intensity, harm is caused to the host and the algae. Apart from rise in temperature, stress due to excess light can also lead to coral bleaching color is lost from coral and the protective pinks and purples are destroyed.
While researching in the Great Barrier Reef and under compactly restricted conditions in the Coral Reef Laboratory of the University of Southampton, the team of researchers created experimental verification that the pink and purple chromoproteins can act as sunscreens for the symbiotic algae by removing parts of the light that might become otherwise harmful.
Dr Jörg Wiedenmann, Senior Lecturer of Biological Oceanography and Head of the University’s Coral Reef Laboratory, who directed the study, says: “The beautiful pink and purple hues that are produced by the coral host are often evoked by chromoproteins; pigments that are biochemically related to the green fluorescent protein (GFP) of the jellyfish Aequorea victoria. In contrast to their green glowing counterpart, the chromoproteins take up substantial amounts of light, but they don’t re-emit light.
“Our results suggest that the screening effect of the chromoproteins could help the algae to enter the new tissue. Once the symbiont population is fully established, the light levels in the tissue decrease as the algae use most of the light for photosynthesis. As a consequence, the genes of the chromoproteins are switched off again which allows the coral to save the energy required for their production.”
Green fluorescent proteins (GFP) similar to pigments are accountable for the brilliant coloration of many reef-building corals and have been anticipated to act as photoprotectants. However, their role remains divisive because the purposeful mechanism has not been clarified. Direct evidence to support a photoprotective role of the non-fluorescent chromoproteins (CPs) that form a biochemically and photo-physically distinct group of GFP-like proteins have been provided. Based on annotations of Acropora nobilis from the Great Barrier Reef, they explored the photoprotective role of CPs by analyzing five coral species under controlled conditions. In vitro and in hospite analyses of chlorophyll excitation show that screening by CPs leads to a fall in chlorophyll excitation corresponding to the spectral properties of the specific CPs present in the coral tissues. Between 562 and 586 nm, the CPs maximal absorption range, there was an up to 50 % reduction of chlorophyll excitation. The screening was steady for established and regenerating tissue and amongst symbiotic clades A, C and D. Moreover, among two differently pigmented morphs of Acropora valida grown under identical light conditions and hosting subclade type C3 symbionts, high CP expression correlated with reduced photodamage under acute light stress.
This study has helped a long way in providing knowledge about the impact of stress levels on corals due to loss of different pigments. Also in artificial set up when we are growing corals, we can use these evidences to study color change that might appear and the various consequences of the same.
