Autofluorescence in plants

Question

I recently found myself on the Wikipedia page for autofluorescence and got confused. I saw a picture of a hazel flower under a microscope that seemed to be glowing. What is causing the cells to produce light? How does that work?

In: Biology

Answer 1

Autofluorescence, as you may have read on the wiki page, happens when certain molecules absorb light (a photon) and re-emit a photon. In reality that’s *fluorescence* but since scientists sometimes artificially add fluorescent dyes, the molecules’ own fluorescence (without any added stuff) is called *autofluorescence* just to differentiate between the two.

Normally, when light shines on an object (or molecule, etc) some wavelengths (think of them as “some colors”) get absorbed and some get reflected. The reflected colors are the ones you see, and the rest of the light that got absorbed is converted to heat, etc.

For certain molecules, when light shines on them there is an additional step (other than the absorption and reflection I discussed above). Some light still gets reflected, but the light that gets absorbed can do one of 2 things: either it just gets converted to heat as above, or if it is *juuust* the right wavelength, it can get re-emitted as a different wavelength. That’s fluorescence.

As a side note, the wavelength is usually higher, meaning the photon lost energy in the process of being absorbed and re-emitted. So if purple light was absorbed, the molecule might re-emit a red or yellow or green photon.

Certain molecules, particularly cyclic/aromatic ones (aromatic in the chemical sense, not the common sense), are good at fluorescing. This is because aromatic molecules contain double bonds that have the ability to shift around, and those shifting double bonds are really good at absorbing light, dissipating a little bit of its energy, and re-emitting the light.

So in a sense, your answer for what is fluorescing is right there on the wiki page: it gives you a list of molecules. Many of them, like NADH/NADPH, melanin, chlorophyll, retinol, tyrosine, etc are aromatic, which accounts for their fluorescence.