... Objective research based on a subjective experience is not going to end well.
Pain is a sensation that is subjective. Yes, there are objective things you can measure that say "This should be painful", but you cannot actually judge, through any objective means if that is actually the case or not.
And that's just with another human being involved.
Since we have a reasonable understanding on what a human being means when they say they're in pain (by inference to our on personal experience), and we can objectively measure biological responses that correlate with what most people describe as things that cause pain, we can infer that these objectively measurable physiological responses have some relationship to the completely subjective experience that is referred to as pain.
In studying animals, we don't even have the ability to ask if they feel pain, but we can typically infer from their reactions that they do, mostly insofar as they resemble the reactions of a person that is in pain.
To ask if a plant feels pain however, leaves us with little to go on.
You are asking what the subjective experience of a plant is, when it suffers damage, when a lot of the physiological responses correlating with the subjective experience of pain in humans (and animals), are missing.
I could well ask, does a rock feel pain?
Here, there aren't even measurable biological processes. But since I've asked a question in terms of what the subjective experience of being a rock is, and can find no objectively measurable process that correlates with anything I know of that can be called a 'feeling' (which is a subjective, not objective statement), I am left with two possible conclusions, but no way of verifying them.
1. - The rock has no 'feelings', and does not experience anything at all, of any description. Thus, talking about what it is like to be a rock is rather meaningless.
2. - The rock does feel or experience something, but this is so far removed from the subjective experience of being human, that no meaningful comparison can be made, and thus there is no possible way for a human being to gain any meaningful insight into what it's like to be a rock.
Now, I realise you're talking about plants, but that is rather my point. Subjective experience cannot be measured. You cannot know what it is like to be anything other than yourself, and thus, objective measurements can only identify processes which appear to correlate with such subjective experiences.
If you find such a correlation, you can then use it to infer things about the nature of the subjective experience for another, but only insofar as the measurable traits bear similarities with something that correlates with your own experience.
Inherently, this causes two problems:
Firstly, correlation of objectively measurable traits does not actually imply that your experience is anything like that of another with similar traits, and there is no real way of knowing how similar the experiences actually are, even if the objectively measurable correlated traits are identical.
Secondly, as the subject of your hypothesis becomes further removed from your own physical characteristics, the probability of it's experience resembling your own becomes increasingly unlikely. Thus, the less you have in common with something you are experimenting on, the more difficult it becomes to make meaningful statements about what it's subjective experiences might be like.
And thus, this experiment is, realistically, outside the scope of what science can really answer.
Since you are framing a question on the subjective experience of plants in terms of their objectively measurable physiological responses, all you can realistically note, is that plants respond to being damaged. But that tells you very little about what that experience is like for the plant.
And 'feeling' pain is not an objectively measurable trait. That goes against what it means to 'feel' something.
I can quantify my pain, because I can talk. But nothing I can say, and nothing that I can measure can let you experience what it means when I say I'm in pain.
Now consider what that means for measuring pain in animals, who cannot talk...
Or in plants, who cannot even react in a way a human being would recognise...
Sometimes, I think scientists don't understand the limitations of their own field.
