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.

拟南芥 ( Arabidopsis thaliana ) 保卫细胞中的淀粉在一天开始时被葡聚糖水解酶 α-AMYLASE3 (AMY3) 和 β-AMYLASE1 (BAM1) 迅速降解，以促进气孔打开。该过程通过质膜 H ⁺ -ATP 酶下游的趋光素介导的蓝光信号激活。目前尚不清楚保卫细胞淀粉降解如何与光调节膜运输过程结合以精细控制气孔打开动力学。我们报告说，在amy3 bam1突变体中，穿过保卫细胞质膜的 H ⁺ 、K ⁺和 Cl ^-转运没有改变，这表明淀粉降解产物不会直接影响转运离子的能力。酶定量显示，蓝光照射 30 分钟后， amy3 bam1保卫细胞具有与野生型相似的苹果酸水平，但显着改变了糖稳态，几乎检测不到 Glc 的量。因此，Glc，而不是苹果酸，是拟南芥保卫细胞中主要的淀粉衍生代谢物。我们进一步表明， amy3 bam1突变体中淀粉降解受损导致打开 40 分钟的时间常数增加。我们得出的结论是，黎明时淀粉的快速降解是维持细胞质糖库所必需的，这显然是快速气孔打开所必需的。因此，亚细胞区室之间代谢物的转化和交换通过膜离子转运协调细胞的能量和代谢状态。