Yes, actually post - not simply comment on another user's post or share another user's post, but create your own post on the topic for which you searched. They say it's all about "starting conversations," making it so that it's easier for users to join the discussion about certain topics in real-time.
Here's what they had to say:
Today we're introducing a new feature that lets you share directly from Google+ search results, and contribute to a topical Google+ stream. For example, if you search for basketball and then want to make a post about how your favorite team or player is doing, you can share right from the search results.
Just look for the sharebox after searching on Google+, and you'll see an opportunity to "join the discussion" about whatever you've searched for.
When you post from the search results page, it automatically includes a link back to the original search stream. This way others can join the active conversation as it unfolds.
When you search a topic (in this case "SOPA") within Google+, you'll now see a new box above the activity stream. It will prompt you to "Join the discussion" about your topic. From there, you can make a post - photo, link, video, plain text, whatever.
Each post made from the search results include a link back to the activity stream on the specific topic - they'll say "Shared from the Google+ ________ stream." Presumably, this will prompt others to join in on the conversation about hot, trending topics.
Considering that Google is adding more Google+ content to regular Google searches in order to "personalize" these results (Search Plus Your World), is it only a matter of time before people can post to their Google+ page straight from the the main Google SERP?