Reddit reviews Plant Survival: Adapting to a Hostile World

To piggy back a little; the chemical components of which you speak are collectively refereed to as secondary metabolites. These are also where humans get many other intoxicants, from opium to marijuana; cocaine to kat.

Then some plants, notably grasses, have a mutualism with endopytic fungi that also produce secondary metabolites for the plant in exchange for sugars.

Another plant, notably the sensitive plant literally closes it's leaves.

For more very cool stuff, check out David Attenborough's the Private Life of Plants episode 5.

Also, try Plant Survival by Brian Capon (author of Botany for Gardeners).