Looks like edema. If so, not a problem.

GardenWeb has a Hydroponics Forum you might like to investigate -
http://forums.gardenweb.com/forums/hydro/

Here is a link that might be useful: Hydroponics Forum

on one leaf???

one leaf does not make a disease...

and would support jeans suggestion.. of a boo boo ..lol ...

ken

Here is a link that might be useful: Edema means swelling caused by fluid in your body's tissues.

I so totally agree with your philosophy of not freaking out when one finds ONE bug, or a couple of questionable leaves on outdoor plants or gardens. However, one is particularly careful when growing crops in g'houses where there is little to no room for error when first sees a disturbing sign. I've seen whole g'house crops go to expensive, and sometimes ineffective treatment to cure crop of diseased plants simply because the operator did not do due diligence in scouting and catching a disease when it was present in just a few plants sitting on benches of a monoculture. I scouted daily, but when I found something I thought wasn't 'right' but was unsure of the reason, it got quarantined away from other plants until I could ascertain what was going on, or treat it. It allowed me to run my operation without a lot of failure or chemicals. The poster should keep an eye on this, as my first take is if it isn't minor insect damage or environmental, it may be virus.

One leaf with bumps doesn't suggest virus.

As for edema, use this search phrase "edema in plants" -- but no quotes

Here is a link that might be useful: edema in plants

That is why I suggested environmental first. Oedema is environmental.