title: Guard cell photosynthesis is critical for stomatal turgor production, yet does not directly mediate CO2 - and ABA-induced stomatal closing.
abstract: Stomata mediate gas exchange between the inter-cellular spaces of leaves and the atmosphere. CO2 levels in leaves (Ci) are determined by respiration, photosynthesis, stomatal conductance and atmospheric [CO2 ]. [CO2 ] in leaves mediates stomatal movements. The role of guard cell photosynthesis in stomatal conductance responses is a matter of debate, and genetic approaches are needed. We have generated transgenic Arabidopsis plants that are chlorophyll-deficient in guard cells only, expressing a constitutively active chlorophyllase in a guard cell specific enhancer trap line. Our data show that more than 90% of guard cells were chlorophyll-deficient. Interestingly, approximately 45% of stomata had an unusual, previously not-described, morphology of thin-shaped chlorophyll-less stomata. Nevertheless, stomatal size, stomatal index, plant morphology, and whole-leaf photosynthetic parameters (PSII, qP, qN, FV '/FM' ) were comparable with wild-type plants. Time-resolved intact leaf gas-exchange analyses showed a reduction in stomatal conductance and CO2 -assimilation rates of the transgenic plants. Normalization of CO2 responses showed that stomata of transgenic plants respond to [CO2 ] shifts. Detailed stomatal aperture measurements of normal kidney-shaped stomata, which lack chlorophyll, showed stomatal closing responses to [CO2 ] elevation and abscisic acid (ABA), while thin-shaped stomata were continuously closed. Our present findings show that stomatal movement responses to [CO2 ] and ABA are functional in guard cells that lack chlorophyll. These data suggest that guard cell CO2 and ABA signal transduction are not directly modulated by guard cell photosynthesis/electron transport. Moreover, the finding that chlorophyll-less stomata cause a 'deflated' thin-shaped phenotype, suggests that photosynthesis in guard cells is critical for energization and guard cell turgor production.
authors.affiliation: Division of Biological Sciences, Cell and Developmental Biology Section, University of California San Diego, La Jolla, CA, 92093-0116, USA.
authors.forename: Tamar
authors.initials: T
authors.lastname: Azoulay-Shemer
authors.affiliation: Division of Biological Sciences, Cell and Developmental Biology Section, University of California San Diego, La Jolla, CA, 92093-0116, USA.
authors.forename: Axxell
authors.initials: A
authors.lastname: Palomares
authors.affiliation: Division of Biological Sciences, Cell and Developmental Biology Section, University of California San Diego, La Jolla, CA, 92093-0116, USA.
authors.forename: Andisheh
authors.initials: A
authors.lastname: Bagheri
authors.affiliation: Umeå Plant Science Centr, Department of Forest Genetics and Plant Physiology, Swedish University of Agricultural Sciences, S901 83, Umeå, Sweden.
authors.forename: Maria
authors.initials: M
authors.lastname: Israelsson-Nordstrom
authors.affiliation: Division of Biological Sciences, Cell and Developmental Biology Section, University of California San Diego, La Jolla, CA, 92093-0116, USA.
authors.forename: Cawas B
authors.initials: CB
authors.lastname: Engineer
authors.affiliation: Biology Department, Center for Genomics and Systems Biology, New York University, New York, NY, 10003, USA.
authors.forename: Bastiaan O R
authors.initials: BO
authors.lastname: Bargmann
authors.affiliation: Division of Biological Sciences, Cell and Developmental Biology Section, University of California San Diego, La Jolla, CA, 92093-0116, USA.
authors.forename: Aaron B
authors.initials: AB
authors.lastname: Stephan
authors.affiliation: Division of Biological Sciences, Cell and Developmental Biology Section, University of California San Diego, La Jolla, CA, 92093-0116, USA.
authors.forename: Julian I
authors.initials: JI
authors.lastname: Schroeder
mesh_terms: D000040:Abscisic Acid / Q000378:metabolism*; D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D002245:Carbon Dioxide / Q000378:metabolism*; D002734:Chlorophyll / Q000378:metabolism; D010788:Photosynthesis / Q000235:genetics / Q000502:physiology*; D018515:Plant Leaves / Q000378:metabolism / Q000502:physiology; D054046:Plant Stomata / Q000235:genetics / Q000378:metabolism* / Q000502:physiology*; D030821:Plants, Genetically Modified / Q000235:genetics / Q000378:metabolism / Q000502:physiology
chemical_list: D002734:Chlorophyll; D002245:Carbon Dioxide; D000040:Abscisic Acid
keywords: Arabidopsis thaliana; CO
  2; abscisic acid; chlorophyll; chlorophyllase; guard cell; photosynthesis; stomata; turgor