Inter-company po : storage location of the supplying plant

Dear.

For an inter-company purchase order I have this problem : after saving the po the system donu2019t determine any storage location for the supplying plant.

I need to determine a specific storage location after creating the po because this location is linked to an mrp area.

I know that I can determine storage location using shipping point but only when I create the delivery for the inter-company po.

How can determine the storage location of the supplying plant after creating the po ?

Thanks for your help.