Plant Suffering
Branches and stems should be looked at for swelling, bumps etc. Roots should be looked at for insect damage. Also look at other plants in the environment: growing conditions, maintenance, has it been pruned lately, animal damage, sunlight, etc. Plants need to be manicured just as you do.
Also, plants feel stressed by vehicle traffic, construction, gas leaks, excavation, spraying in the area, spills of some kind. These are all the same thing that stress you and other humans out.
Plants, too, recoil from detrimental sensations. Research by Alan Bown of Brock University in Canada showed that, ten seconds after an insect crawls on to a leaf, the plant secretes a paralysing agent (called gamma aminobutyric acid) that attacks the intruder’s nervous system. Bown explained that plants distinguish between harmless contact from raindrops and the action of caterpillar feet. Not only that, but having been attacked by insects, plants repair their wounds by releasing the chemical superoxide, which helps to prevent infection.
But in June 2002, researchers in Bonn found that plants emit ethylene gas when under attack. The scientists also attached microphones to the vegetation and observed that whereas the plants normally emitted a bubbling sound, under attack from insects, they gave off piercing screeches. Scientists at the Baylor University Medical Centre in Dallas have measured the chemical response of plants to being pulled up, peeled, cooked and eaten. The results, said Professor Barry Lindzer, showed that “plants initiate a massive hormone and chemical barrage internally when they suffer any kind of injury”. He continued: “This response is akin to the nerve response and endorphin release when an animal is injured. We cannot ignore the similarities.” Scientists from Michigan State University say that plants have a rudimentary nerve structure that allows them to feel pain. “The nervous system is un[der]developed, but it is there.”
They even respond similarly in that aspirin blocks pain in plants as well: http://www.scienceblog.com/community/older/1998/A/199800488.html
Sources:
http://www.pioneerthinking.com/plantdiagnosis.html
http://brianoconnor.typepad.com/animal_crackers/2004/08/lobsters_plant_.html