No. Do not try to use a 450W PSU on a card that requires reccommended of 500W. First: you'd have some performance problems, your GPU wouldn't be using its full potential. Even 500W is questionable. I'd get something OVER 500W as they're more capable and hey, it doesn't hurt if you have a bigger PSU.
what will happen if i connect to the pci-express slot.
Its not recommended to hook up a card that recommends 500Watts. If you connect it to a PCI-E slot it will not even work because it needs power, and if it does work it will be performing at its lowest. You may even run into damaging your system.
Try to find an Antec VP series >500watt or a seasonic >500watt psu.The corsiar VS >550watt or CX >500watt should do fine too. if the other brands aren't available.