Guard cell photosynthesis is critical for stomatal turgor production,yet does not directly mediate CO2‐ and ABA‐induced stomatal closing |
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| Authors: | Tamar Azoulay‐Shemer Axxell Palomares Andisheh Bagheri Maria Israelsson‐Nordstrom Cawas B Engineer Bastiaan O R Bargmann Aaron B Stephan Julian I Schroeder |
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| Affiliation: | 1. Division of Biological Sciences, Cell and Developmental Biology Section, University of California San Diego, La Jolla, CA, USA;2. Ume? Plant Science Centr, Department of Forest Genetics and Plant Physiology, Swedish University of Agricultural Sciences, Ume?, Sweden;3. Biology Department, Center for Genomics and Systems Biology, New York University, New York, NY, USA |
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| 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. |
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| Keywords: | guard cell chlorophyll chlorophyllase photosynthesis
CO
2
abscisic acid stomata turgor
Arabidopsis thaliana
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