Photosynthesis and Space Fungus
Two weeks ago I talked about howLin et al. modified tobacco plants toexpress cyanobacteria Rubisco, with the eventual goal of getting plants to perform photosynthesis as efficiently as cyanobacteria. This already seems to be fairly sci-fi-ish, and I think it will already be really neat when that succeeds, but why stop there? Photosynthesis in plants can be tinkered with a bit more. For instance, you could modify plants and use them to power your electronic devices. You could try to imitative photosynthesis to power your electronics. You could potentially modify plants so that they can use something other than visible light for photosynthesis.
Here is a very brief review of how the light-dependent reaction in photosynthesis works in plants. This becomes a bit more relevant later on. In chloroplasts, there are chlorophyll pigments. When a photon hits one of the pigments, the pigment absorbs the photon, loses an electron and passes it on to a primary acceptor. The electron keeps getting passed on, until it leads to NADP being reduced to NADPH to form a proton gradient – a form of energy harvested to make ATP.
College-level light reactions
These pigments together absorb light in the 400 to 700 nm range in the electromagnetic radiation spectrum. Although I can’t find the source anymore so I can’t guarantee the soundness of this theory, an interesting thought is that this range exists because the evolution of photosynthesis began underwater. Water is actually not very transparent – it only lets in light at wavelengths between 400 and 700 nm. Similarly, this is also likely why we call this the visible range – because the evolution of eyesight had also begun underwater.
If you want to make your plant work outside of the visible range, there is not much of a point in going towards longer wavelengths (for example infrared) since they just don’t provide as much energy as visible light. Absorbing an IR photon just won’t be enough to sufficiently excite an electron. Shorter electromagnetic radiation wavelengths, however, are higher in energy and much more effective. If you start off at the end of the UV radiation and go towards shorter wavelengths towards gamma radiation, this radiation is called ionizing radiation. On Earth, and also on the international space station we’re protected from a lot of it by the magnetosphere, which is a protective area formed by the Earth’s magnetic field, blocking away things like the solar winds. Further away from it though, ionizing radiation is essentially everywhere, so it may be worth looking into modifying plants so that they can make use of it. Perhaps these plants could be grown in greenhouses on other planets, or be used in terraforming.
Ionizing radiation is, unfortunately, ionizing. That is, it’s strong enough to remove electrons from atoms, leaving behind charged particles. When the radiation hits cells, it can leave them in a poor state, with free radicals and DNA damage. It can be hard to imagine a plant making use of it. However, there are fungi that can do just that.
Plants usually heed the warning
They are called radiotrophic fungi, and they use gamma radiation as their source of energy. The ionizing radiation of the ionizing radiation, and we’re not entirely sure yet about how they do it.
These fungi were originally found growing around and inside the Chernobyl Nuclear Power Plant. Some were growing on the walls of the damaged reactor, and some were growing in the old cooling water for the reactor core. They also happily grow around space stations, no matter how much they’re unwanted there. They grow on walls. They grow on electronic equipment.
The radiotrophic fungi have also been around for quite a while. There are a lot of their spores in the sedimentary layer from the early Cretaceous period, which happened over 65 million years ago.
Despite all this gamma radiation, so far the fungi look nothing like The Hulk. Instead, they just look like mold. Mold that evolves very quickly and ruins cleaning efforts. Black mold, due to it using melanin as a pigment.
Unfortunately these fungi appear in quite a few human diseases, so it doesn’t seem like some strains might be edible, no matter how much one would want to consume black mold. However, if instead of mold coating spaceship walls it were, say, strawberries, or really any plant that’d probably actually be pretty cool.
These radiotrophic fungi are called melanized fungi because they use the melanin to harvest the energy from the gamma rays. But how is this not damaging the fungus? And how are they harvesting this energy - are they using the gamma radiation in photosynthesis? In chemosynthesis?
The key component is the melanin. It’s actually a pretty neat pigment. For one, it actually protects against UV light and solar radiation, which helps explain why these fungi are so resilient. Melanin is really good at this; it can absorb all visible and UV radiation, and now it also seems to be able to do this for gamma radiation. It also arranges itself into a sphere to body-block the inside of the fungus from radiation, and it also quenches free radicals.
If the melanin were used as a pigment in photosynthesis, like earlier with the chlorophyll, it would absorb the gamma radiation, which would excite an electron, which would further go into photosynthesis. So far, instead of the gamma radiation just being captured for use in photosynthesis and kicking off an electron, the absorption of gamma radiation also seems to change the structure of the melanin, which improves its electronic configuration of melanin so that it becomes even better at energy transduction. What happens next is a complete mystery.
So the bottom line is, we’re still not sure how the space fungus does what it does, but the melanin is very useful to it. It protects the fungus from damage from ionizing radiation, and it also lets the fungus thrive on gamma radiation as an energy source. It looks like melanin has a lot of promise in the modification of plants, so hopefully we’ll see some research going in that direction.