New Approaches to the Biology of Stomatal Guard Cells

Abstract

CO2 acts as an environmental signal that regulates stomatal movements. High CO2 concentrations reduce stomatal aperture, whereas low concentrations trigger stomatal opening. In contrast to our advanced understanding of light and drought stress responses in guard cells, the molecular mechanisms underlying stomatal CO2 sensing and signaling are largely unknown. Leaf temperature provides a convenient indicator of transpiration, and can be used to detect mutants with altered stomatal control. To identify genes that function in CO2 responses in guard cells, CO2-insensitive mutants were isolated through high-throughput leaf thermal imaging. The isolated mutants are categorized into three groups according to their phenotypes: (i) impaired in stomatal opening under low CO2 concentrations; (ii) impaired in stomatal closing under high CO2 concentrations; and (iii) impaired in stomatal development. Characterization of these mutants has begun to yield insights into the mechanisms of stomatal CO2 responses. In this review, we summarize the current status of the field and discuss future prospects.

CIRCADIAN CLOCK ASSOCIATED1 (CCA1) and the Circadian Control of Stomatal Aperture

“…The maximum stomatal aperture for both SGC2 and SGC24 was similar to wild type but occurred later, at ZT4. Leaf temperature is a useful indicator of transpiration (Negi et al, 2014), and Figure 2C and Supplemental Table S1 show that wild-type leaf temperatures decreased well before lights-on, consistent with increased stomatal opening and transpiration, while temperatures of SGC leaves remained high until lights-on. Together, these results strongly suggest that SGC guard cells are unable to predict daily dark-to-light changes.…”

Enhanced Stomatal Conductance by a Spontaneous Arabidopsis Tetraploid, Me-0, Results from Increased Stomatal Size and Greater Stomatal Aperture

“…Leaf temperature is a convenient indicator of transpiration and can quickly reveal phenotypes with altered stomatal behavior (Negi et al, 2014). We used infrared thermal imaging to investigate stomatal responsiveness to changes in [CO 2 ] in 374 Arabidopsis ecotypes (Takahashi et al, 2015).…”

“…Investigating mutants provides abundant knowledge about the genes involved in the stomatal opening or closure response (Negi et al, 2014) and development (Pillitteri and Torii, 2012) and relationships among these genes. On the other hand, natural accessions like Me-0 have desirable traits for studies of stomatal movement and anatomy.…”

The Transmembrane Region of Guard Cell SLAC1 Channels Perceives CO2 Signals via an ABA-Independent Pathway in Arabidopsis

“…Blue light activates a H + -ATPase that induces plasma membrane hyperpolarization to drive K + uptake through inward K + channels, causing stomatal opening (Kinoshita and Hayashi, 2011). By contrast, when guard cells perceive a high CO 2 concentration, ozone, and the plant hormone abscisic acid (ABA), anion channels are activated and the efflux of anions induces plasma membrane depolarization that activates outward K + channels, causing stomatal closure (Kim et al, 2010;Kollist et al, 2011;Negi et al, 2014).…”