Plants respond to anesthetics, some can react to touch/electricity/heat with rapid movement(thigmonasty), they can sense when they are being damaged, some can even display short-term memory.
But do they feel pain? They have no pain receptors. They have no nervous system. They can feel pressure/vibrations, and even respond to it, but that's it.
I feel that we should presume consciousness, pain, emotions, etc, in all living beings, until most rigorously proven otherwise, because just because we may not understand non-human, non-mammalian or non-animal living beings as well as ourselves does not mean that they cannot experience whatever equivalents their consciousness, bodies or minds allow them to.
My argument is that all living things can feel pain, regardless of how it manifests for them.
Eating animals is trickier. You’re eating processed plants, so you’re still harming plants by eating them, but you’re harming an order of magnitude more plants (due to the inefficient conversion from plant to meat), and you’re harming animals as well. There’s therefore a very strong argument to be made that eating meat is immoral.