Using simple Google chrome extension developed by Crossrider, you can now integrate your Facebook and Twitter stream into Google+. You can get these extension Crossrider.com or directly from Google Web Store.
If you want to integrate Twitter into Google+ you need to install Google+Tweet chrome extension which allows you to tweet, share photos, videos and location directly from Google+.
And if you choose to integrate Facebook into Google+ then you should install Google+Facebook chrome extension.
NOTE: You must connect your Facebook/Twitter account with Google+(Learn how to connect). Secondly, buttons might not display if you are using Internet explorer.