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Well, Luminescence really but I liked the alliteration.

Would there be any reason or mechanic why plants may develop that glow in the dark? Ideally they would do so in response to stimulus such as touch, but continual or periodic glowing would also be acceptable.

Is there a plausible mechanism through which they both could develop the ability and have an evolutionary reason to do so. Most of the reasons why animals do it (such as distracting predators, luring in food, or attracting a mate) do not apply to plants.

I know we've genetically engineered plants to glow through bioluminescence, but I'm not aware of any cases where they have naturally developed the idea. Really I'm looking for a scenario where a "glowing forest" (or at least some glowing plants within a forest) could evolve naturally and be relatively widespread on a world.

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First off, there are lots of different ways organisms can glow, luminescence, fluorescence, and phosphorescence are all subtly different ways for organisms to produce light. I'm going to assume you just care about having glowing plants of any sort and so will focus on evolutionary reasons for "why" they might glow instead of "how". (Although the "how" is pretty easy, they just make the appropriate proteins).

Light is primarily used as a signal by living things. The most likely reason for plants to make light is to try to communicate a message to other organisms. But what would a plant want to say? Lots of things! I'll give a few examples that came to mind below.

Attracting symbionts: Many plants already produce flowers with bright colors in order to attract insect pollinators. It's not a far stretch to suggest they might emit light at night in order to attract nocturnal insects.

Warning predators: Aposematism is a fancy term for the use of warning colors. Lots of animals utilize bright coloration to advertise the fact that they are poisonous, or foul-tasting, or otherwise unpleasant to potential predators. Some plants use their coloration in this way already. Plants could step up their warning game by emitting light as well if they felt so inclined.

While the two above suggestions would work, they are simply extrapolating from existing visual cues that plants use. The following are some more... creative suggestions.

Self-defense: Plants suffer from all sorts of small parasitic insects like aphids and caterpillars. Imagine if in response to injury plants glowed in the affected area. The glow would serve to attract predators that would eat the insects eating the plant. The dark insects would be highlighted against the glowing plant leaf or stalk.

Synchronizing something: Another suggestion is for plants to communicate with each other. Perhaps they want to synchronize their flowering times, or pollen release. Plants are known to be sensitive to light in many ways already, from phototropism to knowing what time of year it is. A glowing forest could help synchronize them all.

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Evolving light generation is not that difficult an issue, it seems fairly common. The reason is more difficult.

Maybe a tree that is pollinated exclusively by something similar to hummingbirds? A light generating tree would allow the birds to feed during night, this would be of great value to the birds as hummingbirds have fast metabolisms and low energy reserves. Thus the birds would end up spending nights at the tree. Hummingbirds are generally assumed to be worthwhile to trees as they provide pollination and eat insects to get proteins.

A touch response version might make sense if that attracted predators eating herbivores the plant wants to get rid of. Alternately the leaves could explode, creating a brief flash. The plant could use nitrocellulose or other nitrated compounds for this for this. The benefit would be that a herbivore trying to eat such plants would simply fail and given how jumpy most herbivores are probably be scared enough to avoid such plant in the future. Nitrocellulose (or other explosive) would also act as energy and nitrogen storage. Usually high energy compounds attract herbivores, but not if they explode on contact.

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  • $\begingroup$ Just in case, it is not obvious. I wrote the pollinator part before reading Samuels answer. I didn't think it is necessary to remove to avoid duplication. $\endgroup$ – Ville Niemi Mar 5 '15 at 22:23
  • $\begingroup$ It's a fairly different example of a pollinator. I certainly think it adds to the discussion. $\endgroup$ – Samuel Mar 5 '15 at 22:33
  • $\begingroup$ @Samuel Well, I also wrote the comment before reading your answer... But yes, having two separate ideas how light might improve pollination is an improvement. $\endgroup$ – Ville Niemi Mar 5 '15 at 22:37
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They would do it for the same reason plants flower: to attract pollinators.

Imagine there is a place where fireflies are ubiquitous. If a plant develops the ability to be bioluminescent, it can attract fireflies looking for a mate, similar to the mimicry seen with existing plants. Flashing, touch sensitivity, or continual glowing could all evolve depending on the pollinator that is co-evolving with the plant.

enter image description here

Bee orchid flower resembles a female bee closely enough to attract males in search of a mate

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If a planet had a slow rotation and so a long day and a long night, it might make sense that a plant might need to harvest as much light as possible during the day.

One possible mechanism to harvest and store extra energy during the long days would be to charge glow-in-the-dark pigments within those plant.

During the long days, the pigments not only could function as a sun-screen, but also convert harmful ultraviolet into useful (for photosynthesis) visible light.

During the night, the glow gives a small amount of light for the plant to harvest for photosynthesis.

Photosynthesis tends to be optimized for certain frequencies of light. Some articles suggest that red and blue light have the best efficiencies for photosynthesis. Although we think of glow in the dark as just the green-white glow, but there are pigments that produce a variety of colors, including red and blue, which is what our plant might do to further boost the efficiency of this process.

The plant would glow, then, as a bi-product of this energy storage, and so it wouldn't take energy away from a plant's metabolism.

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