Server :: Ownership For Multiple Groups To A Single Share?

I have configured a file server with samba and winbind in RHEL5.I am able to allot permission for the active directory groups to my Linux folder.No issues.But i want to set multiple groups of active directory to get ownership to a single directory. Say there are 3 groups a,b,c to have permissions to a folder of the Linux machine.

Code:

chown -R root:Active_directory_group_name path_to_linux directory

I have set

Code:

chmod 770 /myshare

meaning that user and group would have full rights to /myshare

Code:

chown root:a

works great I tried with the option of

Code:

chown -R --reference=/etc/shares_own.txt /myshare

In reference file(shares_own.txt) i gave the entry as

Code:

root:a,b,c

This is not working.