β-carotene Protects From Solar Radiation

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Biological Strategy

Halophile algae

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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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Protists

Kingdom Protista (“the very first”): slime molds, giant kelp, red and brown algae

Protists are a numerous, diverse group of organisms that, in the simplest definition, are defined by what they are not. Protists are not plants, animals, fungi, or bacteria. Some protists, like Plasmodium, are harmful parasites that cause malaria. While many are small, obscure, and go unnoticed, others are important foodstuffs. The largest protist in the world, giant kelp (Macrocystis pyrifera), is utilized by humans and marine species for food and shelter.

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Dunaliella salina algae protect themselves from the effects of solar ultraviolet radiation by producing immense quantities of β-carotene to quench the damaging effects of reactive oxygen radicals.

Dunaliella salina algae is bombarded with the full brunt of solar UV (ultraviolet) radiation and has evolved a novel mechanism for defending itself from the radiation’s damaging effects. More than 8% of its dry body mass is β-carotene, more than any other organism that produces the compound. The algae produces β-carotene in response to UV stress and localizes it to lipid droplets within its chloroplasts. In that location it is able to absorb and neutralize the damaging oxygen radicals produced from excessive UV and sun exposure.

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Last Updated October 5, 2016

References

“Dunaliella salina Teodoresco is a green alga capable of producing high concentrations of carotenoids, i.e. more than 8% of dry weight, when stressed. These carotenoids [mostly β-carotene] are stored in lipid globules.” (Kleinegris et al. 2010:645)

“When Dunaliella salina cells are stressed, they start to produce carotenoids. The green cell which is dominated by the chloroplast starts to turn orange. The chloroplast shrinks, chloroplast membranes decrease in size and carotenoid- containing lipid globules are formed.” (Kleinegris et al. 2010:646)

“Dunaliella salina stores secondary carotenoids (predominantly β-carotene) in lipid globules in the chloroplast when cultivated under stress conditions. Non-stressed cells are dominated by the chloroplast, emitting red fluorescence originating from the chlorophyll in the thylakoid membranes. When the cells are stressed, the red fluorescence from chlorophyll partly disappears as the thylakoid membranes are broken down. At the same time, the cells start to produce carotenoid globules and green fluorescence appears simultaneously. Dunaliella salina cells show this distinct difference in red and green fluorescence pattern between non-stressed and stressed cells.” (Kleinegris et al. 2010:648)

Journal article

Carotenoid fluorescence in Dunaliella salina

J Appl Phycol | 16/02/2010 | Dorinde M. M. Kleinegris, Marjon A. van Es, Marcel Janssen, Willem A. Brandenburg, René H. Wijffels

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