Spatial and Temporal Dynamics of Electrical and Photosynthetic Activity and the Content of Phytohormones Induced by Local Stimulation of Pea Plants

Abstract

A local leaf burning causes variation potential (VP) propagation, a decrease in photosynthesis activity, and changes in the content of phytohormones in unstimulated leaves in pea plants. The VP-induced photosynthesis response develops in two phases: fast inactivation and long-term inactivation. Along with a decrease in photosynthetic activity, there is a transpiration suppression in unstimulated pea leaves, which corresponds to the long-term phase of photosynthesis response. Phytohormone level analysis showed an increase in the concentration of jasmonic acid (JA) preceding a transpiration suppression and a long-term phase of the photosynthesis response. Analysis of the spatial and temporal dynamics of electrical signals, phytohormone levels, photosynthesis, and transpiration activity showed the most pronounced changes in the more distant leaf from the area of local stimulation. The established features are related to the architecture of the vascular bundles in the pea stem.

Keywords: Pisum sativum; abiotic stress; electrical signal; photosynthesis; phytohormones.

Figure 1

Scheme of the experiment: local stimulation by burning tip of the upper fully developed leaf (L_S), recording of electrical signals, measurement of photosynthetic parameters, transpiration intensity measurement, quantification of phytohormones in unstimulated leaves (L₁, L₂, L₃). E₁, E₂, and E₃ are electrodes, which were placed on the petioles of the first, second and third leaves, respectively; E_R is the reference electrode.

Figure 2

Variation potential (VP) induced by local burning of a pea leaf: (A) the typical record of electrical reaction; (B) VP amplitude in the first, second and third leaves, located below the stimulated leaf; (C) the time interval between stimulation and the VP occurrence in the first, second and third leaves. (A): the red arrow indicates the moment of stimulation. (B,C): different letters denote significant differences between columns, p < 0.05.

Figure 3

Changes in photosynthesis activity induced by variation potential (VP) in the first, second and third leaves, located below the stimulated leaf: (A) the typical records of non-photochemical quenching (NPQ) changes in the first, second and third leaves; (B) amplitudes of NPQ changes in the first, second and third leaves; (C) the typical records of Φ_PSII changes in the first, second and third leaves; (D) amplitudes of Φ_PSII changes in the first, second and third leaves; (E) correlations between the amplitude of the photosynthesis response and the VP amplitude. Correlations were determined for simultaneous recording of electrical signals and photosynthesis responses on separate plants (n = 8). Different uppercase letters denote significant differences between columns of fast phase, different lowercase letters denote significant differences between columns of long-term phase, p < 0.05.

Figure 4

Dynamics of leaf temperature induced by local burning. The moment of stimulation corresponds to the point of 0 min. ∆t is the temperature difference between the corresponding leaves of stimulated and unstimulated plants.

Figure 5

Time course of changes in the phytohormones abscisic acid (ABA) and jasmonic acid (JA) induced by local burning. The moment of stimulation corresponds to the point of 0 min. * indicates that difference from control value (0 min) were significant (p < 0.05).

Figure 6

Hypothetical scheme of long-distance signal propagation. Three-dimensional diagram of the vascular bundles in the stem of Pisum sativum and schematic cross sections of internodes and nodes. All the changes in the vascular bundle system occur at the nodal region and this is the reason for omitting the internodes in the figure. Dotted line indicates the pathway of long-distance signal from the stimulated leaf (L_S) to the second unstimulated leaf (L₂). Dashed line indicates the pathway of long-distance signal from the stimulated leaf (L_S) to the first unstimulated leaf (L₁).

Figure 7

Dependence of the VP amplitude, VP velocity, the amplitude of the hormonal response and the photosynthesis response on the distance from the area of local stimulation according to the hypothetical scheme of long-distance signal propagation.