Fronds Hyperaccumulate Arsenic

a large bright green fern plant grows outwards

Biological Strategy

Ladder brake fern

AskNature Team

Image: Katie Wasserman / Unsplash / Some rights reserved

Detoxification/Purification of Air/Water/Waste

Ecosystems must be effective at cleaning air, water, and waste because so much of what is in the air, water, and waste is valuable to organisms as resources. In contrast to functions that detoxify or purify at the organism level, this is at a larger scale. To be effective at the ecosystem level, it isn’t the individual efforts of a few organisms that detoxifies and purifies, but the actions of a wide diversity of organisms each contributing to the whole. For example, as water flows through an ecosystem, either aboveground or in the soil, a diversity of organisms take different actions to slow it down, capture excess nutrients from it, and break down harmful chemicals into more benign ones.

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Protect From Chemicals

Chemicals are everywhere in the bodies of living organisms and their external environments. While most chemicals are valuable or benign, some are toxic, including those used for defense (such as the mucus that protects clownfish from an anemone’s stinging tentacles). Even naturally-occurring chemicals, such as arsenic, must be managed to reduce their impact. Some living systems have strategies to break down harmful chemicals, alter them into less toxic forms, physically prevent chemicals from harming sensitive tissues, and more. For example, some herbivorous mammals can digest toxic compounds in plants because they have a particular enzyme that helps them process poisonous plant compounds.

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Store Chemical Entities

Chemical entities include elements such as carbon and metals, and compounds such as nutrients and proteins. Living systems must often store chemical entities–for example, for food or protection–temporarily or for long periods; the latter is synonymous with sequestration. Because chemical entities can react with other chemicals, living systems must store these entities so that they are stable and out of the way (for long-term storage) or readily available when needed (for temporary storage). An example of temporary storage is found in crustaceans such as crabs, which must shed their external skeletons as they grow. But first, a crab must absorb as much calcium carbonate from its shell as possible, storing the compound in its blood until the crab can use it to grow a new exoskeleton.

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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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Fronds of ladder brake ferns hyperaccumulate toxic arsenic using a special transporter protein that spatially isolates the chemical in vacuoles.

“The fern Pteris vittata can tolerate 100 to 1,000 times more
arsenic than other plants. Jody Banks, a professor of botany and plant
pathology, and David Salt, a professor of horticulture, uncovered what
may have been an evolutionary genetic event that creates an arsenic pump
of sorts in the fern.

“‘It actually sucks the arsenic out of the soil and puts it in the
fronds,’ Banks said. ‘It’s the only multi-cellular organism that can do
this.’…

“Banks and Salt found that the encoded by [an isolated] gene ends up in
the membrane of the plant cell’s vacuole. Salt said the protein acts as
a pump, moving arsenic into the cell’s equivalent of a trashcan.

“‘It stores it away from the cytoplasm so that it can’t have an effect
on the plant,’ Salt said.

“Banks said understanding how the Pteris vittata functions
with arsenic could lead to ways to clean up arsenic-contaminated land…

“The plant might have evolved to accumulate arsenic, Banks and Salt
theorized, as a defense against animals or insects eating them.” (ScienceDaily 2010)