If you have a valid permit to carry weapons issued by ANY state (you do not have to be a resident of that state), it is now honored by Iowa. Your defensive weapon (it can be a knife or a long gun, as well as a handgun, but no "offensive weapons") does NOT have to be concealed, though I recommend it. There is very little experience here with open carry other than in hunting areas.
If you have a PCW then manner of carry in your vehicle (a motorcycle in this case) is immaterial. If, however, you DON'T have a permit, the gun will have to be transported unloaded, in a closed and fastened case (does not have to be locked) that is too large to be concealed on your person - or in a separate compartment (trunk) not accessible by an occupant.
Iowa has no special "no guns" zones. Just stay off school property (felony) and out of the buildings in the Capitol Complex in Des Moines. Also, federally prohibited zones, such as the Post Office, Federal Buildings and facilities and the Corps of Engineers federal reservoirs (Saylorville, Rathbun and Red Rock. (The locks and dams on the Mississippi too, I believe.) Some local governments have recently passed local resolutions or ordinances "banning" weapons on some or all of their property, but these local rules are illegal and void under the state preemption clause of state law. That doesn't mean you couldn't get hassled, but chances are slim. "No Guns" signs at businesses have no force of law in Iowa, though you could be charged with trespass if you don't leave when asked.
I believe this information to be accurate. Check Iowa Code Section 724 or www.handgunlaw.us for more details.