Measures of stomatal size, density, and index in Kl-4, Ga-0, Chi-1, and Col-0.

<p>(A) Guard cell lengths, which were used as a measure of stomatal size. (B) Stomatal densities. (C) Stomatal index. Data presented are means ± SE (<i>n</i> = 3). No significant differences were observed between the four ecotypes.</p

Relative sensitivities to environmental factors among Kl-4, Ga-0, Chi-1, and Col-0.

<p>The diagram summarizes the relative sensitivities of Kl-4, Ga-0, Chi-1, and the reference ecotype Col-0 to CO₂, light, humidity, and ABA. Kl-4 and Col-0 show similar levels of sensitivity to changes in RH. Chi-1 and Ga-0 show similar levels of sensitivity to ABA.</p

Stomatal conductance in <i>Arabidopsis</i> ecotypes that have demonstrated a low CO₂ responsiveness.

<p>The plants were exposed to 0 ppm CO₂ for 2 h and then transferred to 1,000 ppm CO₂ for 1.5 h at 40% RH. Relative conductance levels (Relative <i>g</i>_<i>s</i>) were calculated as (<i>g</i>_<i>s</i> at 1,000 ppm CO₂)/(<i>g</i>_<i>s</i> at 0 ppm CO₂); large values represent small responses. Data presented are means ± SE (<i>n</i> = 3). The commonly used model ecotype Col-0 is highlighted in red and three particularly unresponsive ecotypes that were selected for further experiments are shown in yellow.</p

The phenotype of Kl-4, Ga-0, and Chi-1, which exhibit low CO₂ responsiveness.

<p>(A) Thermal imaging of the three selected ecotypes Kl-4, Ga-0, Chi-1, and the commonly used ecotype Col-0. Plants were subjected to 0 ppm CO₂ for 2 h and then 1,000 ppm CO₂ for 1 h at 40% RH. The subtractive image on the right shows that the largest temperature changes were exhibited by Col-0. (B) Time courses of stomatal conductance (<i>g</i>_<i>s</i>) in response to changes in CO₂ concentration in Kl-4, Ga-0, Chi-1, and Col-0. Col-0 is more responsive to changes in CO₂ concentration than Kl-4, Ga-0, Chi-1. (C) Sizes of stomatal apertures at low and high CO₂ concentrations. Plants were subjected to 0 ppm CO₂ for 2 h and then transferred to 700 ppm CO₂ for 1 h at 40% RH with 150 μmol m^-2 s^-1 photosynthetically active radiation. (D) The relative changes in stomatal aperture (relative stomatal aperture) were calculated as (stomatal aperture in 0 ppm CO₂)/(stomatal aperture in 700 ppm CO₂). Large values represent small responses. Data presented are means ± SE (<i>n</i> = 60) of five independent experiments. Significant differences from Col-0 at <i>p</i> < 0.05 (Student’s t test) are indicated by asterisks.</p

Natural Variation in Stomatal Responses to Environmental Changes among <i>Arabidopsis thaliana</i> Ecotypes

<div><p>Stomata are small pores surrounded by guard cells that regulate gas exchange between plants and the atmosphere. Guard cells integrate multiple environmental signals and control the aperture width to ensure appropriate stomatal function for plant survival. Leaf temperature can be used as an indirect indicator of stomatal conductance to environmental signals. In this study, leaf thermal imaging of 374 <i>Arabidopsis</i> ecotypes was performed to assess their stomatal responses to changes in environmental CO2 concentrations. We identified three ecotypes, Köln (Kl-4), Gabelstein (Ga-0), and Chisdra (Chi-1), that have particularly low responsiveness to changes in CO2 concentrations. We next investigated stomatal responses to other environmental signals in these selected ecotypes, with Col-0 as the reference. The stomatal responses to light were also reduced in the three selected ecotypes when compared with Col-0. In contrast, their stomatal responses to changes in humidity were similar to those of Col-0. Of note, the responses to abscisic acid, a plant hormone involved in the adaptation of plants to reduced water availability, were not entirely consistent with the responses to humidity. This study demonstrates that the stomatal responses to CO2 and light share closely associated signaling mechanisms that are not generally correlated with humidity signaling pathways in these ecotypes. The results might reflect differences between ecotypes in intrinsic response mechanisms to environmental signals.</p></div