Plants Respond to Attacks from Herbivores
Recent research on plants has elucidated their multiple defense mechanisms. Plants have physical structures that protect them against herbivores. One of my favorite are glandular trichomes which “secrete secondary metabolites including flavonoids, terpenoids, and alkaloids that can be poisonous, repellent, or trap insects and other organisms, thus forming a combination of structural and chemical defense.”
Plants respond to attacks by herbivores by creating more of these little organelles. Scientists know this is happening by examining the numbers of trichomes before and after an insect attack. They have studied both trees (gray willows and gray alders) and herbaceous plants (wild radish and pepper grass). The range of increase is usually between 25 to 100 percent; however, induction of 5 to 10 times as many trichomes has been observed.
Trichomes have important social and economic effects on our society. THC, the psychoactive chemical in marijuana is secreted by trichomes. Consequently, if you search for trichomes on the web you will find many articles on how to increase the number of trichomes on cannabis plants.
This fact raises interesting evolutionary questions. For example, did cannabis survive and flourish because the plants wigged-out herbivores or did they survive because gardeners embraced them due to them chilling-out farmers and gardeners.
Quote from: War, Abdul Rashid, et.al. (2012) “Mechanisms of Plant Defense against Insect Herbivores” Plant Signaling & Behavior 7:10, 1306-1320; October 2012