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 . " The researchers discovered that   _
the alarm was increased by chemical messengers the wounded leaf raised danger signals by tiny currents the whole plant was aware of the risk through different signals proteinase inhibitors expanded the warning to the plant's surface