To minimize the fitness-imperiling stress caused by phytophageous insects, plants have evolved many defensive adaptations. These plant defenses against herbivory are generally categorized as either tolerance or resistance. Tolerance traits reduce the detrimental effects of herbivore damage on plant fitness without affecting the herbivore. In contrast, resistance traits either directly or indirectly reduce the amount of damage a plant receives by repelling potential herbivores or impairing their performance. While tolerance mechanisms in plants remain nearly uncharacterized on the molecular level, the signal pathways leading to herbivore resistance have been extensively studied. As plants areellknown to show resistance responses to herbivory in not only locally attacked but also distal, undamaged leaves, the signals mediating these so-called systemic responses have received extensive attention. Among the signals proposed to be capable of transmitting information about herbivore attack from the site of wounding to the rest of the plant is the 18-aa polypeptide systemin. Systemin has long been thought to be the mobile wound signal in tomato (Solanum lycopersicum), but according to the revised model, it plays a central role in tomato’s wound response acting at or near the site of wounding by amplifying the jasmonate-derived mobile wound signal. So far, resistance responses to insect herbivory have been studied mainly in crop plants such as tomato. An important question thus arises: do the above-mentioned findings apply to related but undomesticated species. The present thesis aimed to address this question by studying the defense responses of an undomesticated relative of tomato, black nightshade (Solanum nigrum), in general, and the role of systemin, in particular.