Calcium dynamics during trap closure visualized in transgenic Venus flytrap

Area of Science:

• Plant biology
• Biochemistry
• Mechanobiology

Background:

• The Venus flytrap (Dionaea muscipula) exhibits rapid leaf closure in response to mechanical stimuli.
• This response typically requires two stimuli within 30 seconds, suggesting a memory mechanism.
• The precise biological system and signaling pathway for this memory remain largely unknown.

Purpose of the Study:

• To investigate the role of calcium dynamics in the Venus flytrap's stimulus memory and leaf closure response.
• To link the observed signal memory to specific changes in cytosolic calcium concentration ([Ca2+]cyt).

Main Methods:

• Utilized transgenic Venus flytraps engineered with a calcium (Ca2+) sensor.
• Applied controlled mechanical stimuli to sensory hairs on the leaf blade.
• Monitored changes in cytosolic calcium concentration ([Ca2+]cyt) using the Ca2+ sensor.
• Compared calcium wave propagation speeds with other plant species and stimuli.

Main Results:

• A single mechanical stimulus initiated a calcium (Ca2+) wave spreading from the sensory hair to the leaf blade.
• A second stimulus, if applied within approximately 30 seconds, elevated [Ca2+]cyt to a threshold level, inducing leaf closure.
• The cytosolic calcium concentration ([Ca2+]cyt) decayed over time, and a delayed second stimulus failed to reach the closure threshold.
• Calcium waves from mechanical stimulation in Dionaea were significantly faster than those induced by wounding in other plants.

Conclusions:

• Calcium dynamics are directly linked to the stimulus memory mechanism in Venus flytraps.
• The threshold-based calcium increase is crucial for triggering the rapid leaf closure response.
• This study provides insights into the rapid movement mechanisms in plants and their evolutionary basis, highlighting the role of calcium signaling.