Sun has made a recommendation of tire width for what they feel is safe for that rim. You may be able to put a 32 on it but it's not recommended because your pushing the edge, but anything beyond 32 is asking for trouble. Go to this web site and check out the rim chart:
http://www.sheldonbrown.com/tire-sizing.html Keep in mind this chart is conservative just as Suns recommendations are, but they do that for safety. Another way to look at it is by a mathematical rule of thumb for tire sizing is 1.8-2.2 times your rim width
Note, that just as Sun, the Chart recommends nothing more then two sizes under and two sizes over of the middle size; again you could go an additional one size, but should not go more then that.
If you want to squeeze a 45 onto rim with a max size rating of 28 then you do so at your own risk, I am not recommending you do that under any circumstance. And a 35? Well some manufactures 35 may be closer to 32 then a true 35 and those will fit, but so what? you still have a 32 it's just marked 35.