If you meant defaulting Purchase Order distribution accounts from the (backing) requisition, then the accounts from requisitions will default into the autocreated PO.
If you seek to default distribution accounts for Purchase Requisition using Projects, then the account generator need to have customized rules defined to default account for project enabled distributions based on the Project/Task/Organization/Expenditure Type/Date combination entered.
This note is an extract from the user's guide, and has good detail on defaulting rules of accounts for Purchase Documents:
How Does The Account Generator Default The Accounts In Oracle Purchasing? (Doc ID 1067139.1)
Hope this helps.