I have known that plants have a CNS for ages. Its well accepted in plant biology. Thats why plants have chemicals that get us high, because these chemicals are part of the plants CNS.
One example, is they most certainly have an endocannabinoid system, like animals, to deal with shock, toxicity and adaption, like in animals.
In that sense, they definately "detect" pain. Whether they feel it or not is as philosophical as asking the same question of animals, or even other people - you cant directly know..
Of course any animal that is a lower mammal or less cannot anticipate pain, in the way a primate or dolphin/whale/elephant/human can. We can actually prove this, via behaviours (unlike with plants, which have no behaviours per se).
That in itself is a reason vegans should check their heads:-
Lower mammals, birds and fish, do not think and feel like us. They certainly feel, and think, but not exactly like us -there are proven differences...
And plants - we cannot tell what they feel, short of complex studies of their CNS, electrochemical communications, and other abstract things..So whether they feel things is simply a mystery...
The assumption that plants feel less, and lower mammals feel more is simply an overextension of a biological empathy intended for other humans. In other words, its easier to feel sorry for, or close to, something human like, than something un human like. Anthrocentric thinking, and biological empathy run amok..
Thats why nobody has any major problem killing insects, but anything cute, fluffy with big eyes is close enough to a human baby to get the neurochemical reaction.
Ever thought about why they are always saving the koala or the dolphins but no one gives an arse about the giant weta, or the vampire bat?
and whats freakier -many plants are still alive when you chop them up, or eat them...so if they do feel pain, unlike animals we have no sensitivity towards it (we dont ensure the plant dies quickly, or if its even dead before we eat it...we just mercilessly hack and chew)
From a purely objective point of veiw, I cannot say I know one way or another if plants feel. They have no behaviours (other than electrochemical signals and growth patterns), so its impossible to tell without very detailed science. They have all the rudimentary NT elements chemically of a CNS, and they have receptors, so they do have a CNS of some kind, and its somewhat similar to that in animals - the chemicals have similar roles as with animals. Beyond that, who knows....
Animals (lower), I know they feel, but also that they dont feel all the same things as people, such as anticipation of pain.
As such, objectivily, i would never choose to be vegan for ethical reasons.
I can certainly choose not to eat monkeys, whales or elephants on the grounds they are most likely more sensitive than lower mammals, and if I was more concerned about the suffering of my food than my own health (which seems pretty dumb), i would perhaps eat lower on the evolutionary scale (like fish for example), but theres not evidence for anything else, and not all that much good comparitive science on the experiences of animals or their intelligence anyway...
(its hard science to perform, lets face it, especially without assumptions galore - a good example is that some primates are smarter in the wild for tool use, because they teach each other - but isolate one in a lab, and you dont see that same range of behaviours...and primates are better with sign language or icons, but cant vocalise - yet they can still learn language to some degree, similar to a 7 ish year old human...by imposing human limitations on how they learn - such as taking them from their peer group, or using vocalised words, weve already missed a great deal of their intelligence...I imagine those obstacles get greater the further from human an animal or plant is)
However, even though id never be vegan, if I had to eat a baby to survive, trapped in the artic, I am sure my chemicals would give me trouble!!! :P :D..
Lets just hope the baby has horns, mandibles, bug eyes, six legs, is green, or has a trunk and leaves, and then ill be fine..:D