Plant hormones (Literature sources on phytohormones and plant signalling)

Author: Leonie Verhage.

The Plant Journal (2021)

Excerpts: "At least four systemic signals travel through the vascular bundles of the plant: the electric wave, the calcium wave, the reactive oxygen species (ROS) wave, and the hydraulic wave."

"However, there is still a lot unknown about the interactions between the different signals. Therefore, Mittler and his group wanted to do something that had not been achieved before: measure all four waves under the same experimental conditions and find out how they interact. In this issue, they present their results (Fichman and Mittler, 2021)."

"These findings show that RBODH, PDLP5, and GLR are differentially involved in systemic signaling in response to wounding or high light stress, at least in the ROS and hydraulic waves. This suggests that different stress signals trigger different types of systemic signals."

Authors: Ralf Oelmüller

International Journal of Molecular Sciences (2021)

Abstract: "Adaptation and response to environmental changes require dynamic and fast information distribution within the plant body. If one part of a plant is exposed to stress, attacked by other organisms or exposed to any other kind of threat, the information travels to neighboring organs and even neighboring plants and activates appropriate responses. The information flow is mediated by fast-traveling small metabolites, hormones, proteins/peptides, RNAs or volatiles. Electric and hydraulic waves also participate in signal propagation. The signaling molecules move from one cell to the neighboring cell, via the plasmodesmata, through the apoplast, within the vascular tissue or—as volatiles—through the air. A threat-specific response in a systemic tissue probably requires a combination of different traveling compounds. The propagating signals must travel over long distances and multiple barriers, and the signal intensity declines with increasing distance. This requires permanent amplification processes, feedback loops and cross-talks among the different traveling molecules and probably a short-term memory, to refresh the propagation process. Recent studies show that volatiles activate defense responses in systemic tissues but also play important roles in the maintenance of the propagation of traveling signals within the plant. The distal organs can respond immediately to the systemic signals or memorize the threat information and respond faster and stronger when they are exposed again to the same or even another threat. Transmission and storage of information is accompanied by loss of specificity about the threat that activated the process. I summarize our knowledge about the proposed long-distance traveling compounds and discuss their possible connections."