Integration of Electrical Signals and Phytohormones in the Control of Systemic Response

pH change accompanying long-distance electrical signal controls systemic jasmonate biosynthesis

Local damaging stimuli cause a rapid increase in the content of the defense phytohormone jasmonic acid (JA) and its biologically active derivative jasmonoyl-L-isoleucine (JA-Ile) in undamaged distal tissues. The increase in JA and JA-Ile levels was coincident with a rapid decrease in the levels of the precursor 12-oxo-phytodienoic acid (OPDA). The propagation of a stimulus-induced long-distance electrical signal, variation potential (VP), which is accompanied by intracellular changes in pH and Ca2+ levels, preceded systemic changes in jasmonate content. The decrease in pH during VP, mediated by transient inactivation of the plasma membrane H+-ATPase, induced the conversion of OPDA to JA, probably by regulating the availability of the OPDA substrate to JA biosynthetic enzymes. The regulation of systemic synthesis of JA and JA-Ile by the Ca2+ wave accompanying VP most likely occurs by the same mechanism of pH-induced conversion of OPDA to JA due to Ca2+-mediated decrease in pH as a result of H+-ATPase inactivation. Thus, the transient increase in intracellular Ca2+ levels and the transient decrease in intracellular pH are most likely the key mechanisms of VP-mediated regulation of jasmonate production in systemic tissues upon local stimulation.

The Long-Distance Transport of Some Plant Hormones and Possible Involvement of Lipid-Binding and Transfer Proteins in Hormonal Transport

Adaptation to changes in the environment depends, in part, on signaling between plant organs to integrate adaptive response at the level of the whole organism. Changes in the delivery of hormones from one organ to another through the vascular system strongly suggest that hormone transport is involved in the transmission of signals over long distances. However, there is evidence that, alternatively, systemic responses may be brought about by other kinds of signals (e.g., hydraulic or electrical) capable of inducing changes in hormone metabolism in distant organs. Long-distance transport of hormones is therefore a matter of debate. This review summarizes arguments for and against the involvement of the long-distance transport of cytokinins in signaling mineral nutrient availability from roots to the shoot. It also assesses the evidence for the role of abscisic acid (ABA) and jasmonates in long-distance signaling of water deficiency and the possibility that Lipid-Binding and Transfer Proteins (LBTPs) facilitate the long-distance transport of hormones. It is assumed that proteins of this type raise the solubility of hydrophobic substances such as ABA and jasmonates in hydrophilic spaces, thereby enabling their movement in solution throughout the plant. This review collates evidence that LBTPs bind to cytokinins, ABA, and jasmonates and that cytokinins, ABA, and LBTPs are present in xylem and phloem sap and co-localize at sites of loading into vascular tissues and at sites of unloading from the phloem. The available evidence indicates a functional interaction between LBTPs and these hormones.

Special Issue "Phytohormones: Important Participators in Plant Growth and Development"

The articles published in the IJMS Special Issue "Phytohormones" are devoted to various aspects of hormonal control of plant growth and development promoting adaptation to normal and stress conditions [...].

Electrical signalling and plant response to herbivory: A short review

For a long time, electrical signaling was neglected at the expense of signaling studies in plants being concentrated with chemical and hydraulic signals. Studies conducted in recent years have revealed that plants are capable of emitting, processing, and transmitting bioelectrical signals to regulate a wide variety of physiological functions. Many important biological and physiological phenomena are accompanied by these cellular electrical manifestations, which supports the hypothesis about the importance of bioelectricity as a fundamental 'model' for response the stresses environmental and for activities regeneration of these organisms. Electrical signals have also been characterized and discriminated against in genetically modified plants under stress mediated by sucking insects and/or by the application of systemic insecticides. Such results can guide future studies that aim to elucidate the factors involved in the processes of resistance to stress and plant defense, thus aiding in the development of successful strategies in integrated pest management. Therefore, this mini review includes the results of studies aimed at electrical signaling in response to biotic stress. We also demonstrated how the generation and propagation of electrical signals takes place and included a description of how these electrical potentials are measured.

Ion Channels in Electrical Signaling in Higher Plants

Electrical signals (ESs) appearing in plants under the action of various external factors play an important role in adaptation to changing environmental conditions. Generation of ES in higher plant cells is associated with activation of Ca2+, K+, and anion fluxes, as well as with changes in the activity of plasma membrane H+-ATPase. In the present review, molecular nature of the ion channels contributing to ESs transmission in higher plants is analyzed based on comparison of the data from molecular-genetic and electrophysiological studies. Based on such characteristics of ion channels as selectivity, activation mechanism, and intracellular and tissue localization, those ion channels that meet the requirements for potential participation in ES generation were selected from a wide variety of ion channels in higher plants. Analysis of the data of experimental studies performed on mutants with suppressed or enhanced expression of a certain channel gene revealed those channels whose activation contributes to ESs formation. The channels responsible for Ca2+ flux during generation of ESs include channels of the GLR family, for K+ flux - GORK, for anions - MSL. Consideration of the prospects of further studies suggests the need to combine electrophysiological and genetic approaches along with analysis of ion concentrations in intact plants within a single study.