Trigger hair thermoreceptors provide for heat-induced calcium-electrical excitability in Venus flytrap

Abstract

Most plants suffer greatly from heat in general and fire in particular, but some can profit from what is called fire ecology.1Dionaea muscipula, the Venus flytrap, is one such plant. In its natural habitat in the Green Swamps, Dionaea often faces challenges from excessive growth of grass and evergreen shrubs that overshadow the plant.2 Without natural fire, the Dionaea populations would decline.3 How does Dionaea survive and even thrive after swamp fires? Here, we ask whether flytraps recognize heat waves at the forefront of swamp fires and demonstrate that a heat-sensor-based alarm may provide a fire survival strategy for them. In this study, we show that flytraps become electrically excited and close in response to a heat wave. Over a critical temperature of 38°C, traps fire action potentials (APs), which are interconnected with cytosolic Ca2+ transients. The heat-induced Ca2+-AP has a 3-min refractory period, yet traps still respond to cold, voltage, and glutamate. The heat responses were trap specific, emerging only when the trap became excitable. Upon heat stimulation, the Ca2+ wave originates in the trigger hair podium, indicating that the mechanosensory zone serves as a heat receptor organ. In contrast to the human heat receptor, the flytrap sensor detects temperature change rather than the absolute body temperature. We propose that by sensing the temperature differential, flytraps can recognize the heat of an approaching fire, thus closing before the trigger hairs are burned, while they can continue to catch prey throughout hot summers.