Can plants feel pain?
I think before discussing "pain", we'd probably have to discuss whether plants actually can "feel". 

This is also down to how one wants to define this (hence "opinion based"), but I assume most people (?) would equal the lack of a brain/neurons with the lack of the capability to feel. And I presume so do you, as you show by using the tag "neuroscience". 

In which case the answer to your question "Can plants feel pain?" is "no", regardless of whether plants react to damage through the release of chemicals or not, and whether one would like to classify this as "pain" or not.