You can pretty much insert GFP into anything. This is the outside of a leaf with GFP tagged to an aquaporin that localizes to the plasma membrane. The cells are known as pavement cells, but look like puzzle pieces. When I first saw this image, I admit my first thought was that it kind of looked like a brain, though clearly there are many differences in appearance between this and a brain- I just see brains everywhere. There are so many amazing images with GFP- I strongly encourage you to google them and check it all out if you want to see some beautiful scientific images. For basic info about GFP, see here.
[Image is by Susan Schiffer and found here]