related fields of profile2

i am using profile2 module
every user has a department and a designation of that department and both are to be selected from respective dropdowns.
both dropdown are created with content type entities not by taxonomy.

department has 2 fields:
department name, node module element(field type).
department code, text(field type), textfield(widget)

designtion has 2 fields:
Department, Node reference(field type), selecting list(widget)
Designation Name, Node module element(field type)

In Home » Administration » Structure » Profile types » Main profile » Manage fields
it has 2 fields

Department, Node reference(field type), select list(widget) ->displays all departments
Designation, Node reference(field type), select list(widget) ->displays all designations

i want designation list to display designations according to department only not all designations.

Any Drupal Expert. Really Appreciate!