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Comment by eutropia | Hacker News Reader

TFA also acknowledges this:

  > There could well be many other functions that have since joined in with the sleep cycle (such as memory consolidation), but the authors hypothesize that mitochondrial function is the process that underlies all of them. If you need oxygen, then you need sleep!

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> If you need oxygen, then you need sleep!

Do plants sleep? Don't some insects, like flies, live without any sleep?

Plants breathe out oxygen, like we breathe out the other one.

That's true for photosynthesis but don't they still have oxygen respiration (i.e. oxidizing sugar for energy?)

yes, at night they breath oxygen. Maybe they sleep during the day.

But their cells still consume oxygen during the day, don't they? In sunshine they produce more oxygen than they consume, but the cells are still fundamentally powered by mitochondria oxidizing glucose

Perhaps different regions of the plant "sleep" at different times? The plant has no need for high response synchronized behavior at all.

You still consume oxygen when sleeping.

Plants respire oxygen continually, day and night. It's a myth that they only respire at night.

Like every other organism except for anaerobes (mostly microbes, some fungi) they need oxygen in order to burn fuel for cellular processes. Plant cells are doing things day and night.

The origin of the myth is simply that they produce more oxygen via photosynthesis than they respire, and so are net producers of oxygen during the day.

yes, I meant net.

They need oxygen for the mitochondrial electron transport chain to produce ATP. The vast majority of multicellular organisms need oxygen for that reason, and I can count the exceptions on one or two hands (i.e. Pogonophoran tube worms, some anaerobic sponges, a few parasitic helminths).

Plants have chloroplasts that produce oxygen and sugar. But plants also have mitochondria that consume oxygen and sugar and run many of the same metabolic functions as in animals.

Insects do sleep, the paper we're discussing is a study of flies.

No, plants don't sleep, and neither do fungi or single celled organisms. Sleep seems to be a property specifically of animals.

Maybe plants are "always asleep" ?

And pray they never wake

Some plants do change to a "night" configuration though (closing leaves or petals, etc). Not sure if you could call it sleep.

I would be surprised by any organism that can sense its environment and doesn’t change behaviour at night. The difference is pretty extreme, whether its temperature, light or just all other beings changing what they’re doing. Even if you don’t notice yourself, you’ll probably be affected by second-order effects.

The simplest example that seems like it would be an exception to your criteria would be an amoeba.

By which criteria? They do respond to daily cycles. How do you know they do not sleep?

> Across the animal kingdom sleep satisfies most, though not necessarily all, of the following criteria: (1) decreased brain arousal and its behavioral correlate, decreased responsiveness to an animal’s surroundings, which distinguishes sleep from immobile wakefulness (also known as rest); (2) electrical changes in the brain’s activity patterns relative to the waking state; (3) behavioral quiescence, often accompanied by a preferred location and characteristic posture; (4) rapid reversibility, which distinguishes sleep from hibernation, anesthesia and coma; (5) homeostatic regulation, in which lost episodes of behavioral quiescence and low arousal are followed by compensatory (rebound) episodes [10].

https://pmc.ncbi.nlm.nih.gov/articles/PMC5120870/

4 and 5 don't seem to be exemplified by plants.

Across animal kingdom.

And you don't think different criteria might apply to plants? I mean, look, we are just discovering how plants function as a society. They are immobile and 4 and 5 might be caused by the fact that an animal is mobile, at least for the most examples, but where not, it can at least react in some manner. Plants have a very very slow reaction time so to them 4 and 5 don't apply even in waking condition, I mean unless you consider several hours to be a reaction. Let's be frank: we don't know (yet).

What I don't appreciate is an outright dismissal "plants do not sleep".

Would you call it sleep still, if it is so different from what we call sleep?

We know plants have a diurnal cycle and react to sun/day and some visibly change between night and day. If we say that one of these states is less active, we may decide to call it dormant. Dormant comes from latin dormire, which is sleep. So... why not?

Animals have a sleep-wake cycle that is usually synchronized with the day-night (24 hour) cycle of the Earth. But this synchronization is not essential. All animals with nervous system have a sleep-wake cycle, even if they live underground or in the deep ocean, where the day-night cycle has no significant effect. So there must be an actual need for the sleep-wake cycle that is independent of the rotation of the Earth.

I think it should have been “If you need oxygen and have a CNS, then you need sleep.” Other tissues can take oxidative break during wakefulness, but since CNS is _generating_ wakefulness, if it takes a break, by construction there is sleep.

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