At least in they project the plant would glow forever. In this project they add the reactives submerging the leaves in a liquid with nanoparticles that have the reactives, so it locks like they will glow only once.

Also, in spite of the photoshoped tree and the photo that has the brightness so high that the noise level is evident

> The light generated by one ten centimetre (four inch) watercress seedling is currently about one-thousandth of the amount needed to properly read by, but it was enough to illuminate the words on a page of John Milton's Paradise Lost.

this generates a tiny amount of light, don't expect to use it to illuminate the streets like they hope in the article.