Iridescent Thin Layer Provides Photoprotection

bright blue leaves are seen amongst lush green leaves and brown forest floor

Biological Strategy

Twinsorus ferns

AskNature Team

Image: Martin Adamek / Shutterstock / Some rights reserved

Capture, Absorb, or Filter Energy

Energy is naturally available in many forms, including kinetic, potential, thermal, elastic, radiant, chemical, and more. All living systems require energy to carry out their many activities, and have developed strategies appropriate to one or more of those forms. For example, some plants maximize their surface area available for capturing radiant energy from the sun while others have strategies to focus scattered light onto photosynthesizing areas.

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Regulate Cellular Processes

Cells are the basic building blocks of all living systems, so cellular processes dictate how physiological processes occur within those systems. Cells (whether entire unicellular organisms or parts of multicellular living systems) grow, metabolize nutrients (that is, chemically transform them), produce proteins and enzymes, replicate, and move. Cells as part of multicellular systems rarely act alone, instead having ways to signal to start and complete simple to quite complex interactions. How skin heals is a good example of the role of cellular processes. Blood cells called platelets release clotting factors to stop the bleeding; white blood cells rid the area of foreign materials and release molecules to coordinate healing; cells called fibroblasts start rebuilding using proteins called collagen; new blood vessels form; and skin cells called keratinocytes create the new surface.

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Protect From Light

Access to sunlight is crucial to living systems because it’s the primary energy source for life. However, too much sunlight in the form of ultraviolet radiation (UV) can cause damage to living tissues. Therefore, living systems have strategies to filter out some or all UV radiation. For example, some plants that live in areas exposed to long periods of direct sunlight have reflective surfaces (such as white hairs or powder) that reflect UV light.

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Ferns

Class Polypodiopsida (“many footed appearance”): Ferns, horsetails, whisk ferns

Ferns are a class of plants that reproduce without flowers or seeds, but by spores. With over 10,500 known species, ferns are the second most abundant group of vascular plants after angiosperms (flowering plants). Though they can be found in a variety of habitats, ferns prefer moist, humid environments. Ferns first evolved in the Carboniferous Period about 360 million years ago. Today, ferns are grown for food, medicine, ornamental landscaping, and hold importance in culture and folklore. Several species can also remove pollutants from the atmosphere.

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Leaves of tropical rainforest understory plants are protected from excess sun by blue iridescence.

“Iridescent blue-leaved plants grow in the most shady and protected
microclimates of tropical rainforests. Much speculation on the possible
adaptive significance of iridescence has not led to any viable
explanations, as such iridescence actually reduces leaf absorption in
these light-limited environments. We hypothesize that constructive
interference in the wavelengths of 460-485 nm may protect against
photoinhibition and damage via reduced light absorption at those
wavelengths, where other leaves are protected by anthocyanins and
variants of the xanthophyll cycle. We looked for such photoprotection
in three Malaysian understory species polymorphic for blue iridescence:
Begonia pavonina Ridl. (Begoniaceae), Diplazium tomentosum Bl. (Athyriaceae), and Phyllagathis rotundifolia
(Melastomataceae). We collected dark-acclimated leaves before dawn from
plants in Bukit Lanjang Forest Reserve. We tested for differences in
leaf mass, and nutrients in green and blue leaves, and for
increased photoprotection in blue leaves by subjecting both to 30 min
of high irradiance (~1000 µmol m-2 s-1, 400-700 nm) and testing for
differences in transient fluorescence as Fv/Fm for 90 min at 5 min
intervals. All leaves, particularly in B. pavonina had relatively low mass, chlorophyll and N per unit area. In B. pavonina and P. rotundifolia, blue leaves recovered significantly more rapidly from light exposure than green ones, but the differences for D. tomentosum
were not significant. Two of the three understory species thus provide
evidence for a photoprotective function by blue iridescence against
transient exposures to light flecks in these extreme-shade plants.” (Lee et al. 2008)

Lee, David [1], Kelley, John [2], Richards, J.H. [3].
Blue Leaf Iridescence as a By-product of Photoprotection in Tropical Rainforest Understory Plants
http://www.2008.botanyconference.org/engine/search/index.php?func=detail&aid=343

Last Updated September 27, 2017

References

“Iridescent blue-leaved plants grow in the most shady and protected microclimates of tropical rainforests. Much speculation on the possible adaptive significance of iridescence has not led to any viable explanations, as such iridescence actually reduces leaf absorption in these light-limited environments. We hypothesize that constructive interference in the wavelengths of 460-485 nm may protect against photoinhibition and damage via reduced light absorption at those wavelengths, where other leaves are protected by anthocyanins and variants of the xanthophyll cycle. We looked for such photoprotection in three Malaysian understory species polymorphic for blue iridescence: Begonia pavonina Ridl. (Begoniaceae), Diplazium tomentosum Bl. (Athyriaceae), and Phyllagathis rotundifolia (Melastomataceae). We collected dark-acclimated leaves before dawn from plants in Bukit Lanjang Forest Reserve. We tested for differences in leaf mass, chlorophyll and nutrients in green and blue leaves, and for increased photoprotection in blue leaves by subjecting both to 30 min
of high irradiance (~1000 µmol m-2 s-1, 400-700 nm) and testing for differences in transient fluorescence as Fv/Fm for 90 min at 5 min intervals. All leaves, particularly in B. pavonina had relatively low mass, chlorophyll and N per unit area. In B. pavonina and P. rotundifolia, blue leaves recovered significantly more rapidly from light exposure than green ones, but the differences for D. tomentosum were not significant. Two of the three understory species thus provide
evidence for a photoprotective function by blue iridescence against transient exposures to light flecks in these extreme-shade plants.” (Lee et al. 2008)

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