Add purchase_requisition_line_id field, it is id of purchase requisition line from where purchase order line is created, overwrite the make_purchase_order method for add value of purchase_requisition_line_id to record purchase order line, it is help to make best inherit and modification of make_purchase_order method, as can be seen in purchase_requisition_line_description, purchase_requisition_line_analytic and purchase_requisition_requisitor modules.
