Google+ availability for Google Apps accounts
Google+ is available to Google Apps users whose domains are on the new Google Apps infrastructure. You can use your Google Apps account with Google+ only if your domain administrator has enabled the service for your domain. Note that it is up to your domain administrator to determine which products will be made available for your entire domain.
It’s important to note that your administrator has access to any data you store in this account, including your email. Please read the Google Apps Important Privacy Notice for more information.