Threat at One End of the Plant: What Travels to Inform the Other Parts?

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.

Advances about the Roles of Membranes in Cotton Fiber Development

“…Plasmodesmata (PD) are intercellular pores connecting most plant cells and controlling the entry and exit of molecules at cell boundaries [ 49 ]. The fiber PD were initially permeable at 0–9 DPA, closed at 10 DPA, and re-opened at 16 DPA.…”

Lipid peroxidation and stress-induced signalling molecules in systemic resistance mediated by azelaic acid/AZELAIC ACID INDUCED1: signal initiation and propagation

“…In primed tissues, the defense responses are not activated yet. However, if primed tissue is exposed to the same or similar threat, that induced the primed state, the response differs from that of the unprimed tissue, since it activates induced systemic resistance or SAR programs (Conrath et al 2015 ; Fu and Dong 2013 ; Oelmüller 2021 ). Defense priming mediated the AZA/AZI1 results in a faster and stronger activation of defense and antioxidant genes, genes for phytohormones and enzymes involved in the synthesis of defense-related metabolites including volatiles.…”

Signals and Their Perception for Remodelling, Adjustment and Repair of the Plant Cell Wall

“…Extracellular adenosine 5′-triphosphate (eATP) can be considered as an inter-kingdom signaling molecule [ 272 ] and participates in the information transfer between cells from different organisms and systemic signal propagation within the plant [ 273 , 274 ]. Although eATP has long been discussed as a signaling molecule in animals [ 275 , 276 , 277 , 278 ] and plants [ 279 , 280 ], it is not yet clear how ATP is transferred from the cytoplasm to the extracellular space in response to specific signals.…”