What responsibilities can a product owner NOT delegate?

The PO often instructs/requests the DT to help him/her in prioritising the product backlog, and also write user stories from time to time (if required or necessary). This means the PO can delegate his/her work to the team. I would like to know what the PO cannot delegate to the team - which activities the Scrum team cannot/should not perform on behalf of the PO.

Posted By - Gabriel