Figure 1.

(a) Schematic of plant burning, locations of electrodes, and measurements of photosynthetic and spectral parameters. E_L² and E_L² are electrodes, which were placed on the leaflet of the second and fourth leaves, respectively; E_R is the reference electrode. The local burning of the first mature leaf (flame, 3–4 s, approximately 1 cm²) was used for the induction of electrical signals and physiological responses (arrow). A PAM fluorometer Dual-PAM-100, including detector block Dual-DB and emitter block Dual-E, was used for measurements of the quantum yield of photosystem II (Ф_PSII) and non-photochemical quenching of chlorophyll fluorescence (NPQ). A spectrometer S-100 was used for measurement of the reflected light. AL is the actinic light (halogen lamp Osram Decostar, white light, about 630 μmol m⁻²s⁻¹); SPs is the saturation pulses (Dual-PAM-100, 630 nm, 10 000 μmol m⁻²s⁻¹, 300 ms); ML is the measuring light (Dual-PAM-100, 460 nm, 24 μmol m⁻²s⁻¹, 2.5 µs pulses); RL is the reflected light. $WI=\frac{R_{900}}{R_{970}}$ is the water index; R₉₀₀ and R₉₇₀ are intensities of the reflected light at 895–905 nm and 965–975 nm; R_400–500, R_500–600, R_600–700, and R_700–800 are average intensities of the reflected light at broad spectral bands (400–500, 500–600, 600–700, and 700–800 nm, respectively). (b) A spectrum of the reflected light in the pea leaf. (c) Connection between average decrease in WI (ΔWI) and average decrease in the relative water content during soil drought (1–5 d without irrigation). ΔWI was calculated as difference between WI in experiment (under the soil drought) and WI in control; change in the water contents was calculated analogically. R is the linear correlation coefficient.