Simple NSPopupButton and NSTextField bindings question

[Decoder]

Hi All,

I have an array of dictionary which contains two keys- firstName and
lastName and their values, eg.

firstName/ lastName

Steve/ Jobs
Andre/ Agassi
Christiano/ Ronaldo

User interface consists of a pop up button and a text field.

I am displaying first name of users in pop up button. I am able to
show first name of the user selected in pop button in the text field
by using following bindings:

NSArrayController

Content Array - AppDelegate - myArray

NSPopUpButton

content - Array Controller - arrangedObjects - firstName
selected value - AppDelegate - selectionValue

NSTextField

Value - AppDelegate - selectionValue

Here myArray is a property declared as NSArray and selectionValue is a
property declared as NSString declared in AppDelegate class.

Now I am getting clue less to implement this through bindings:
Text field should show last name of user whose first name is selected
in pop up button.

Can anyone suggest me some solution to implement it or is it possible
through bindings?

Thanks,