Thanks, folks. Lemons - how simple!

As suggested above, a little lemon juice will do the trick. This is useful to keep in mind for a lot of things that go brown.

Yes, acidulated water should work fine although you will probably have to weigh them down to keep them submerged, Normally though it's only the chokes that will turn brown when exposed to air. my method for cooking them is normally to braise them with mint. Carciofi alla romana.

Acidulated water! After trimming just make sure to keep them in a bowl of cold tap water with a couple lemons squeezed into it, then added. The acid in the water will stop the artichokes from browning, and when it comes time to cook them, sauteed in olive oil, bacon fat, or roasted in a 400 degree F oven will do the trick.