Calcium dynamics during trap closure visualized in transgenic Venus flytrap.

The leaves of the carnivorous plant Venus flytrap, Dionaea muscipula (Dionaea) close rapidly to capture insect prey. The closure response usually requires two successive mechanical stimuli to sensory hairs on the leaf blade within approximately 30 s (refs. 1-4). An unknown biological system in Dionaea is thought to memorize the first stimulus and transduce the signal from the sensory hair to the leaf blade2. Here, we link signal memory to calcium dynamics using transgenic Dionaea expressing a Ca2+ sensor. Stimulation of a sensory hair caused an increase in cytosolic Ca2+ concentration ([Ca2+]cyt) starting in the sensory hair and spreading to the leaf blade. A second stimulus increased [Ca2+]cyt to an even higher level, meeting a threshold that is correlated to the leaf blade closure. Because [Ca2+]cyt gradually decreased after the first stimulus, the [Ca2+]cyt increase induced by the second stimulus was insufficient to meet the putative threshold for movement after about 30 s. The Ca2+ wave triggered by mechanical stimulation moved an order of magnitude faster than that induced by wounding in petioles of Arabidopsis thaliana5 and Dionaea. The capacity for rapid movement has evolved repeatedly in flowering plants. This study opens a path to investigate the role of Ca2+ in plant movement mechanisms and their evolution.