Mechanosensation in leaf veins

Diethyl ether anaesthesia does not block local touch response in Arabidopsis thaliana

Plants can sense and respond to non-damaging mechanical stimulation such as touch, rain, or wind. Mechanical stimulation induces an increase of cytosolic calcium ([Ca2+]cyt), accumulation of phytohormones from the group of jasmonates (JAs) and activation of gene expression, which can be JAs-dependent or JAs-independent. Response to touch shares similar properties with reactions to stresses such as wounding or pathogen attack, and regular mechanical stimulation leads to changes in growth and development called thigmomorphogenesis. Previous studies showed that well-known seismonastic plants such as Venus flytrap (Dionaea muscipula) or sensitive plant (Mimosa pudica) lost their touch-induced motive responses during exposure to general volatile anaesthetic (GVA) diethyl ether. Here, we investigated the effect of diethyl ether anaesthesia on touch response in Arabidopsis thaliana. We monitored [Ca2+]cyt level, accumulation of JAs and expression of touch-responsive genes. Our results showed that none of the investigated responses was affected by diethyl ether. However, diethyl ether alone increased [Ca2+]cyt and modulated JAs-independent touch-responsive genes, thus partially activating touch response non-specifically. Together with our previous studies, we concluded that GVA diethyl ether cannot block the local rise of [Ca2+]cyt but only its systemic propagation dependent on GLUTAMATE LIKE RECEPTOR 3s (GLR3s) channels.

Revisiting plant electric signaling: Challenging an old phenomenon with novel discoveries

Higher plants efficiently orchestrate rapid systemic responses to diverse environmental stimuli through electric signaling. This review explores the mechanisms underlying two main types of electric signals in plants, action potentials (APs) and slow wave potentials (SWPs), and how new discoveries challenge conventional neurophysiological paradigms traditionally forming their theoretical foundations. Animal APs are biophysically well-defined, whereas plant APs are often classified based on their shape, lacking thorough characterization. SWPs are depolarizing electric signals deviating from this shape, leading to an oversimplified classification of plant electric signals. Indeed, investigating the generation and propagation of plant APs and SWPs showcases a complex interplay of mechanisms that sustain self-propagating signals and internally propagating stimuli, resulting in membrane depolarization, cytosolic calcium increase, and alterations in reactive oxygen species and pH. A holistic understanding of plant electric signaling will rely on unraveling the network of ion-conducting proteins, signaling molecules, and mechanisms for signal generation and propagation.

Early signaling enhance heat tolerance in Arabidopsis through modulating jasmonic acid synthesis mediated by HSFA2

Given the detrimental impact of global warming on crop production, it is particularly important to understand how plants respond and adapt to higher temperatures. Using the non-invasive micro-test technique and laser confocal microscopy, we found that the cascade process of early signals (K+, H2O2, H+, and Ca2+) ultimately resulted in an increase in the cytoplasmic Ca2+ concentration when Arabidopsis was exposed to heat stress. Quantitative real-time PCR demonstrated that heat stress significantly up-regulated the expression of CAM1, CAM3 and HSFA2; however, after CAM1 and CAM3 mutation, the upregulation of HSFA2 was reduced. In addition, heat stress affected the expression of LOX3 and OPR3, which was not observed when HSFA2 was mutated. Luciferase reporter gene expression assay and electrophoretic mobility shift assay showed that HSFA2 regulated the expression of both genes. Determination of jasmonic acid (JA) content showed that JA synthesis was promoted by heat stress, but was damaged when HSFA2 and OPR3 were mutated. Finally, physiological experiments showed that JA reduced the relative electrical conductivity of leaves, enhanced chlorophyll content and relative water content, and improved the survival rate of Arabidopsis under heat stress. Together, our results reveal a new pathway for Arabidopsis to sense and transmit heat signals; HSFA2 is involved in the JA synthesis, which can act as a defensive compound improving Arabidopsis heat tolerance.