Systemic Signaling in the Regulation of Stomatal Conductance

Abstract

Systemic signaling is involved in the regulation of stomatal conductance in response to rapid changes in ambient light and intercellular CO₂ concentration.

Figure 1.

Experimental setup and stomatal conductance measurements. A, Schematic representation of the experimental setup. Boxes with dashed borders represent the cuvette of the gas exchange measuring system and black indicates the treated tissues. A 1-h acclimation period in constant conditions (PAR 600/200 µmol photons m⁻² s⁻¹, relative humidity 60%, temperature 20°C/22°C, and CO₂ concentration 400 µL L⁻¹) was followed by either of the two treatments: darkness after the light period or a rapid increase in CO₂ concentration from 400 to 1,100 µL L⁻¹. Treatments were conducted in three different combinations: treatment simultaneously in the cuvette and the chamber (orange), only in the chamber (yellow), or only in the cuvette (gray). Blue indicates the control treatment. Relative stomatal conductance of the measured (cuvette) leaf (normalized to pretreatment steady-state values) of B. pendula (n = 4), P. tremula × tremuloides (n = 4), and Arabidopsis (n = 6) in response to (B) sudden darkness (lights switched off) or (C) a rapid increase in CO₂ concentration (from 400 to 1,100 µL L⁻¹ over ∼4.5 min). Black and white bars above the figures illustrate the onset and duration of the indicated treatment. Stomatal responses were statistically analyzed by fitting generalized additive mixed models (Wood, 2006) on the treatment responses as functions of time using the software package mgcv (v1.8-17) in R (v3.4.2; R Core Team; http://www.r-project.org/). Generalized additive mixed models are well suited for the analysis of gas exchange data as they do not assume linearity for the response and can take into account the nonindependence of the measuring points. Lines represent the model fits (predicted values) with 95% confidence intervals and dots are the observed relative stomatal conductance values. Asterisks indicate significant differences (adjusted P value < 0.004) between the treatments. The color of the asterisk shows the subject of the pairwise comparison.