Subject: Plants suffer? Vegan = less/more plants suffer? How do plants respond?

I've wrestled with these questions since I saw videos on the net of the cruelty 
inflicted on amimals in many slaughterhouses. (There's a video at 
http://www.youtube.com/watch?v=VIjanhKqVC4, but WARNING, IT'S GRAPHIC). I 
became vegan to avoid contributing to the pain that I think those animals are 
probably feeling. It's been sugested to me, however, that plants might feel 
pain as well, causing me to wonder if there's a point in being vegan after all. 
I've read in many places (including here at madsci) that plants don't have 
nervous systems, but someone asked me how they respond to light, predators, and 
other aspects of their environment without nervous systems and I admit I don't 
know. So my questions are:

1. What are the chances that plants can feel pain?

2. If plants can feel pain, would a vegan contribute to more or less plants 
suffering as compared to someone who eats both meat and plants (I know animals 
eat plants to, but I would think that if one were to measure it, they would 
probably find that vegans eat more plants to replace the meat they don't eat 
and meat eaters eat less vegetables because they can get the same amount of 
food by eating some meat instead).

3. In what ways to plants respond to their environment and how do they do so 
without a nervous system (assuming what I've read about them not having a 
nervous system is true). If they can't "know", for instance, that a predator is 
eating them (as in being able to think "ow, someone's eating me, I'd better 
fight back") how are they able to respond at the right time?

I'm afraid I've obsessed over these questions because I want to do what I think 
is right, and knowing the right answers to the questions would help give me 
some peace of mind.

Re: Plants suffer? Vegan = less/more plants suffer? How do plants respond?