Nanoparticles could turn soon trees into streetlights, according to recent internet stories. Chlorophyll naturally absorbs light of one wavelength of light (400 nm) and gives off some of it as red light. The reason we don't normally see plants glowing is that the amount of 400 nm light they get is too small.
Yen Hsun Su and coworkers have now apparently shown that if you soak aquatic plants in gold nanoparticles, some of the nanoparticles get into the cells. Then when you expose the plants to UV light, the nanoparticles aborb it and emit light at 400 nm, which the chlorophyll in turn absorbs and emits as red light. So leaves could be lit for Christmas all year long, no electricity required.
Despite huge amounts of recent hoopla (stories in RSC's Chemistry World, New Scientist, ElectroIQ, The Cool Gadgets, Earth Times and hundreds of others), the trees in your neighborhood aren't going to be fluorescing any time soon. The system isn't efficient enough to use large scale, they haven't tested any plants except water weeds (Bacopa caroliniana), and gold nanoparticles aren't exactly cheap (although neither are current LED phosphors). I think like GFP-pets, this is far more likely to become a niche toy than an important commercial enterprise, but it's still fun to think about.