How the purple and pink sunscreens of reef corals work
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New
research by the University of Southampton has found a mechanism as to how
corals use their pink and purple hues as sunscreen to protect them against
harmful sunlight. Many reef corals need light to survive, as they benefit from
sugars and lipids that are produced by their light-dependent symbiotic algae.
However, in the shallow water of coral reefs, light levels are often higher
than required by the corals, so paradoxically, the vital sunlight can become
harmful for the algae and their hosts.
Apart
from temperature, light stress is a major driver of coral bleaching -- the loss
of the symbiotic algae that represents a threat to coral reef survival.
Working
in the Great Barrier Reef and under tightly controlled conditions in the Coral
Reef Laboratory of the University of Southampton, the team of researchers
produced experimental evidence 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 led 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.
"GFP-like
proteins were suggested to contribute to the protection of corals and their
symbionts from excess sunlight. This hypothesis has been controversially
discussed as the mechanism as to how these pigments function remained unclear.
At least for the chromoproteins we know now that they have indeed the capacity
to fulfill this function." The researchers also proposed an explanation
for the mysterious phenomenon that some corals accumulate exceptionally high
amounts of chromoproteins in growing areas, such as branch tips or in the
region of healing wounds.
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Dr
Wiedenmann, who is based at the National Oceanography Centre, Southampton,
explains: "These growing areas contain essentially no symbiotic algae, so
much of the light is reflected by the white coral skeleton instead of being
used by the algae. The resulting increased light intensities in the new parts
of the coral represent a potential danger for the algal cells that need to
colonise these areas. Hence, it seems that the corals use a clever trick to
help their symbionts. The higher light intensity switches on the genes that are
responsible for the production of the sunscreening chromoproteins.
"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."
The
research contributes to a better understanding of the coral's response to
environmental stress. Knowledge of the stress resilience of corals is an
important requirement to help predictions of the fate of coral reefs that are
exposed to climate change and various forms of anthropogenic disturbance.
The paper is published in the latest edition of the journal Coral Reefs.
Source: University of Southampton
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Posted by Unknown
on Friday, January 25, 2013.
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