If I am understanding the original question correctly...
A PO and it's items are data objects. They describe some piece of business data (not logic). While I suppose that you could wire up a PO and its items in a Spring container, it doesn't make much sense. These items belong in the database.
The types of objects you wire up in Spring are service objects. This includes any service layer objects, DAOs, utility objects, etc. These object
do something.
So, to answer your question, you wouldn't likely wire up a PO and its related line items in Spring. Those would be kept in a database and retrieve using
JDBC or some ORM solution (like Hibernate).
If (let's say) you decide to use Hibernate. In that case you would wire up (in Spring) a Hibernate session factory and any DAO and service layer objects you need to retrieve the PO and its line items from the database. But the PO and its line items aren't wired...they're in the database.
Does that make sense?