in the books of Harry Potter Plants and animals with surprising characteristics often appear, coming from the author’s imagination. In Nature we can also find examples of plants and animals that seem to defy established definitions. Many of them would be worthy of appearing in one of the young wizard’s books.
When we think about the differences between plants and animals, one of the first that comes to mind is the ability to carry out photosynthesis. During this process, plants (and some bacteria) use light energy to create organic compounds from carbon dioxide. Thus, plants release oxygen into the atmosphere.
Animals, for their part, obtain energy from chemical reactions and carbon comes from organic molecules.
Now, there are exceptions to everything. In this case, we have two very clear examples: the ghost orchid and the photosynthetic salamander.
The ghost orchid and other non-photosynthetic plants
Many orchid species are mixotrophic. This means that they obtain part of their nutrients from symbiosis with fungi. However, there are also certain plants that are obligate microheterotrophs. What does it mean? They do not photosynthesize and are totally dependent on these fungi for nutrients.
There are several species of ‘ghost orchids’. Some of them are able to grow in complete darkness. They do not have leaves or chlorophyll, so they do not carry out photosynthesis.
This phenomenon is not exclusive to orchids. It also appears in other groups of plants. Variants of orchids have even been found that have lost their pigments. It speaks of ‘plantas albinas‘ but, in such specimens, lack of pigments could mean the death of the plant, in case it could not obtain nutrients by symbiosis.
But photosynthesis is not an exclusive process of plants: there are animals that are also capable of carrying it out. Some ‘steal’ algae chloroplasts, the cellular organelles responsible for photosynthesis, in order to take advantage of sunlight.
It is a phenomenon called kleptoplasty. To achieve this, these animals ingest algae and partially digest them, without damaging the chloroplasts. After that, they store them, thus obtaining the ability to use them for a while. Of course, they cannot synthesize new chloroplasts.
For example, there is a sea hare of the genus Elysia that is capable of living for months using sunlight. But perhaps the most beautiful photosynthetic animals are the ‘leaf sheep’, sea slugs of the Costasiella genus.
Other animals, such as some corals, do not capture the chloroplasts, but the entire algae. The coral provides protection to the algae against predators and environmental changes. In return, you get nutrients.
This phenomenon has also been described in clams, anemones, jellyfish, etc.
The spotted salamander is an exceptional case. It is the only photosynthetic vertebrate. The algae enter the salamander eggs. They provide oxygen to the embryo and feed on its waste.
Later studies have shown that algae not only provide oxygen, but also glucose. And, in addition, algae are found within the cells of the spotted salamander embryo and are maintained throughout its life.
Photosynthesis in humans?
Various works have been published on the possible applications of photosynthesis in biomedicine, using microalgae or cyanobacteria.
One of the first contributions was the design of a photosynthetic artificial lung.
As we know, the absence of oxygen can cause serious and irreversible brain damage. In another study, by injecting algae or cyanobacteria into the circulatory system of tadpoles that had suffered from hypoxia, brain activity was restored.
Theoretically this ‘photosynthetic therapy‘ could be applied to various pathologies in which the supply of oxygen through the circulatory system is not sufficient. Even nonexistent. Its usefulness in the treatment of infarcts or ischemia, solid tumors and in tissue regeneration is being investigated. It could even help in organ transplants, in order to keep them viable.
There are already some clinical trials in humans in which photosynthetic biomaterials have been tested to recover damaged areas of the skin, especially in patients with diabetic ulcers.
At the moment, it does not seem that we are going to see ‘green’ human beings, capable of feeding on inorganic compounds and sunlight. It would be a spectacular advance, but we are a long way from that.
María Teresa Tejedor Junco is Professor of Microbiology, University of Las Palmas de Gran Canaria