Plants are living yes, and hormone signals etc happen in them sure. It's not known what causes consciousness though, hell we don't even know why general anesthetics work in humans and we generally only believe them to disrupt consciousness because you ask people about it later and they say they have no recollection, except sometimes when they do so amnesics are often administered as a failsafe.
What do you mean when you say anesthetise a tree? And why is that evidence of sentience? Like lignocaine will work on the nerves in my arm. You could keep my arm alive after removing it from me (at least for a while) and inject lignocaine and observe interrupted nerve signals. Most people don't believe amputated arms to be sentient though.