Brian makes a good point but I think the main thing is what you are talking about is an organism's ability to react to the environment. this is not intelligence. Or sentience. The acid test is: does the organism have neurons?
BTW, some of your phrases bring up the stuff in
The Secret Life of Plants. Keep in mind that none of those experiments were ever replicated. the book has been debunked over and over. And even the authors have admitted to making up the whole thing.
Speaking of something reacting to the environment, just reminded me of something my biology prof showed the class (shoot it must have been 40 years ago). He had an overhead projector and something set up so the class could not see what was on the overhead. He had a glass Petrie dish and we could see a "blob" in a solution. when he added "food" to the Petrie dish the blob reacted to it, moved towards it, and "ate" it. It even left a little trail of excretions. (I think the food was a potassium compound and the solution was an acid, thus causing a strong chemical reaction).
Anyway, the point was there are chemical reactions and then there are conscious reactions. What you see in plants are just chemical reactions
Beegans and bivalve vegans use this same line of reasoning but flip it on its head. Oysters and bees react to the environment. but strictly speaking, have no brains. But this is a can of worms and creates some real puzzles. A good simple approach is that they are biologically classified as animals so they are off the menu. Or you could say that we can't prove they don't feel pain - we do know they have sensory organs. and react to stimuli.
Another thing that people who wish to argue with vegans brings up is the mycorrhizal networks that exist under forests. These even resemble nervous systems.
How animals meet the challenges of surviving in the most iconic habitats on earth.
www.bbc.com