Thread: Photosynthesis by starlight.

Just an idle question here.
Is photosynthesis by starlight possible?
I don't mean any significant or even useful amount of photosynthesis, just like maybe one or two phosphates bound to one or two ADP's over the course of an evening.
I'm going to guess yes. But that's assuming that photosynthesis is like the photoelectric effect, and is dependent on wavelength, not intensity.

Giantevil.

The answer is no. Green plants are adapted to using sunlight. They close down their photosynthetic mechanisms at night. In addition, most of the starlight is the wrong wavelength. In addition, the intensity of starlight is about a million times lower than sunlight. I seriously doubt even single molecules of ATP are produced.

But given enough time and/or altering the genes you could probably breed some to use it? Then again they would likely lose more energy than they gain.

Starlight likely wouldn't be able to make it through the cuticle to the mesophyll where the chloroplast are located.

Originally Posted by GiantEvil

Just an idle question here.
Is photosynthesis by starlight possible?
I don't mean any significant or even useful amount of photosynthesis, just like maybe one or two phosphates bound to one or two ADP's over the course of an evening.
I'm going to guess yes. But that's assuming that photosynthesis is like the photoelectric effect, and is dependent on wavelength, not intensity.

The intensity of the light and its wavelength are both important factors to consider. I think that in plants and cyanobacteria the proton gradient across the thylakoid membrane will collapse or dissipate below a certain threshold intensity and so there will be no synthesis of ATP by the CF1FO-ATP synthase complex. I'm rusty here, but I recall that the magnitude of this gradient is substantial and definitely couldn't be supported by the sort of night time starlight we have here on earth. It is entirely possible that photons from distant stars are absorbed by the photosystems during the day (the stars are still there, afterall). Starlight photons would/could perhaps make an infinitesimally small contribution - one photon in a "jazillion" or whatever. Certainly a fun maths problem for someone to play with. The photon flux is so low at night that we could essentially describe it as being non-existent and certainly useless to the plant since it would be incapable of supporting the massive proton gradient required for ATP synthesis.

Take the next bit with a large pinch of salt: green sulphur bacteria are renowned as the ultimate photon scavengers. They have the ability to photosynthesise in what to our eyes could be described as near darkness or by utilising the black body radiation emitted by deep sea thermal vents. Their bacteriochlorophylls may absorb as little as one photon every eight hours or so. Maybe in an experimental setup we could get them do something in moonlight? The same experiment in starlight has my gut saying "no" quite loudly (I can't back up this claim with data though).