Access Control in Group and Professional Editions

Group Edition doesn’t support field-level security or custom profiles. You can manage field-level security by using the page layout for each object instead. When customers install your app, they can’t define which profiles have access to what. Ensure that your design works for the Standard User Profile. Permission sets can be installed but not updated in GE and PE orgs.

Because field level security is handled by the page layout, any fields you want to be visible must be added to the page layout. This means that for fields to be accessible via the API or Visualforce, they must be added to the page layout.