There are no rules or regulations which prohibit you from teaching any subject at secondary level (assuming your PGCE relates to secondary level). As long as you can convince the school that you're the right person for the job, you're qualified to teach art, maths, english, french, . . .etc, etc. (i.e. your PGCE is a qualification to teach secondary level pupils and, irrespective of your degree studies, is not subject specific).
Any difficulties which might arise in obtaining a post would relate to your ability (or lack of ability) to convince the school that you can do the job. I'm fairly sure that, after a suitable period of study, I could gain qualifications in Art History - andI'm already a qualified teacher - but I think that my total inability to draw or paint even the simplest of subjects would be good reason to refuse me a job teaching Art! You'll need something more than just qualifications if you want to get an art-teaching job. A portfolio of your own work might impress a selection panel but nowhere near as much as experience working on youth art projects (e.g. in a youth club or on a summer scheme) would.
Chris