How to declare several primary zones

[ELISABETH.CHORQUES at ALCATEL.FR]

Hello !
 I work with Bind 8.2.3. But I have a question about definitions of
zones. Is it possible  to declare two PRIMARY zones in the Bind like this
?
 First zone:       branch.toto.root
 second zone: leaf.branch.toto.root
My two zones are declared master zones in my named.conf file and the DNS
name is entered in the SOA records.
My problem is that I cannot update my two zones correctly. When I perform
a "nsupdate" on the second one, the first one is updated.
I know that my two zones are a little odd but I need this cut to separate
two different functions.

Thank you in advance for your answers.

Elisabeth Chorques
Alcatel