Guard Cell Starch Degradation Yields Glucose for Rapid Stomatal Opening in Arabidopsis
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2020-07-01
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Journal Article
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Abstract
Starch in Arabidopsis (Arabidopsis thaliana) guard cells is rapidly degraded at the start of the day by the glucan hydrolases α-AMYLASE3 (AMY3) and β-AMYLASE1 (BAM1) to promote stomatal opening. This process is activated via phototropin-mediated blue light signaling downstream of the plasma membrane H+-ATPase. It remains unknown how guard cell starch degradation integrates with light-regulated membrane transport processes in the fine control of stomatal opening kinetics. We report that H+, K+, and Cl− transport across the guard cell plasma membrane is unaltered in the amy3 bam1 mutant, suggesting that starch degradation products do not directly affect the capacity to transport ions. Enzymatic quantification revealed that after 30 min of blue light illumination, amy3 bam1 guard cells had similar malate levels as the wild type, but had dramatically altered sugar homeostasis, with almost undetectable amounts of Glc. Thus, Glc, not malate, is the major starch-derived metabolite in Arabidopsis guard cells. We further show that impaired starch degradation in the amy3 bam1 mutant resulted in an increase in the time constant for opening of 40 min. We conclude that rapid starch degradation at dawn is required to maintain the cytoplasmic sugar pool, clearly needed for fast stomatal opening. The conversion and exchange of metabolites between subcellular compartments therefore coordinates the energetic and metabolic status of the cell with membrane ion transport.
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published
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32 (7)
Pages / Article No.
2325 - 2344
Publisher
American Society of Plant Physiologists
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08715 - Gruppe Mol. Physiologie der Pflanzen / Plant Molecular Physiology Group
03706 - Widmer, Alexander / Widmer, Alexander
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Funding
166539 - Mechanistic insights into the adaptive plasticity of plant starch metabolism (SNF)
185241 - Rewiring starch metabolism for plant environmental adaptation (SNF)
185241 - Rewiring starch metabolism for plant environmental adaptation (SNF)