When a caterpillar   feeds on a tomato leaf , the plant moves rapidly to meet with a defensive response , systematically releasing " proteinase inhibitors " -- proteins that interfere   with the caterpillar's digestion -- throughout the plant , especially in the leaves .  But how does the message get from the wounded leaf to the rest of the plant ?        Most scientists believed the alarm was spread by chemical messengers until a team of researchers headed by David Weldon-- a biologist at the University of East Anglia in Norwich , England -- made a shocking discovery .  An injured leaf , the researchers found , sends an electrical signal to warn neighboring leaves of upcoming danger . It's a " terribly tiny current " driven by an electrical potential difference of only 20 millvolts   , says Weldon , who measured the voltage after electrodes were attached to the plant's surface .          " Right now , all we can say is that there is a correlation , " Weldon notes . " If you wound the plant , you'll see an electrical signal accompanied by a biochemical response . " To learn more about the reaction , Weldon's team plans to insert electrodes within the pant tissue ( rather than on the surface ) to determine what's going on at the cellular level . The findings may help explain other mysteries surrounding plants . For example , many plants start to flower in springtime , as days grow longer , but plants sense the change in the day length through their leaves , while flowers begin to bloom at the buds   .  " There must be a signal from the leaf to the growing points , " Weldon says . " So far , no one has come up with a convincing chemical mechanism . Maybe an electrical signal is involved . " What is the function of the " proteinase inhibitors " in tomato plants ?
They create nutritional matter They produce electrical signals They protect the plant from insects They cure diseases by changing chemicals