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.

A Theoretical Analysis of Relations between Pressure Changes along Xylem Vessels and Propagation of Variation Potential in Higher Plants

“…This high value of D is hypothesized to be related to the non-laminar water flow in the xylem and the induction of turbulent diffusion [ 5 , 62 ]. However, it is unlikely that turbulent diffusion can transmit a wound substance by tens of centimeters (we simulated the propagation of the wound substance and VP for 10–15 cm using our previous models [ 62 , 63 , 64 ]; the radioactive marker was transmitted for less than 15 cm for 200 s [ 62 ]); in contrast, VP can propagate for 28 [ 65 ]-40 cm [ 46 ] and more.…”

“…Theoretical analysis shows that VP propagation can be stimulated by an increase in the length of the xylem vessel (increase in the rate of VP propagation, decrease in the V VP decrement with an increase in the distance from the damaged zone, increase in x max ). It seems to be unusual and requires further verification; however, it can explain VP propagation over long distances (tens of centimeters [ 15 , 46 , 65 ]) and experimentally detected high rates of VP propagation over such distances (e.g., 20 mm s −1 at a 17–20 cm distance from the burned zone [ 15 ]).…”

“…(i) The single tube is a very simple description of xylem vessels. It does not consider the complicated connections between xylem vessels in plants [ 65 , 72 , 73 ] or the decreasing vessel radius with increasing distance from the basal part of the plant shoot [ 67 ]. Potentially, the last point can be important for simulation of VP propagation in trees (on distances equaling several meters).…”

“…(ii) The model is based on a minimal description of the threshold for VP (as a function of integral of pressure changes) and does not simulate the amplitude of VP, which can be strongly correlated to magnitudes of physiological responses (e.g., photosynthetic response [ 30 ]). It is known that there are differences in the dependence of the VP amplitude on the distance from the damaged zone: the amplitude is not significantly dependent on the distance [ 30 , 46 , 63 ], and the amplitude significantly decreases with an increase in the distance [ 64 , 65 , 69 ]. The type of dependence can be related to the type of stressor: significant changes in the VP amplitude with an increase in the distance are absent after burning and heating but are observed after crushing of leaves in pea seedlings [ 63 ].…”

“…These combined hypotheses can potentially explain the propagation of a wound substance for 10–15 cm [ 62 , 63 , 64 ]; however, it is shown [ 46 ] that VP can propagate for at least 45 cm, with a moderate decrease in the propagation rate and amplitude in grape plants. A high VP propagation rate a long distance from the damaged zone (e.g., 14 mm s −1 at 15 cm from this zone in pea seedlings [ 65 ]) is not in accordance with the combined hypotheses, too.…”