A plant hormone called jasmonate has been found to cause plants to react to touch and control plant growth as a defence against insects and fungal infections.
Jasmonate is released on touch and causes several plant defences, such as increased production of metabolites that make herbivores ill, and stunted growth of certain plants including Arabidopsis, which grows shorter and more slowly when frequently touched.
Researchers from Rice University say that touch is just one signal that causes high levels of jasmonate. They found that plants also release jasmonate according to the plants’ internal circadian rhythm.
Read more at Rice University