Stomatal guard cells are unique in that they have more mitochondria than chloroplasts. Several reports emphasized the importance of mitochondria as the major energy source during stomatal opening. We re-examined their role during stomatal closure. The marked sensitivity of stomata to both menadione (MD) and methyl viologen (MV) demonstrated that both mitochondria and chloroplasts helped to promote stomatal closure in Arabidopsis. As in the case of abscisic acid (ABA), a plant stress hormone, MD and MV induced stomatal closure at micromolar concentration. All three compounds generated superoxide and H₂O₂, as indicated by fluorescence probes, BES-So-AM and CM-H₂DCFDA, respectively. Results from tiron (a superoxide scavenger) and catalase (an H₂O₂ scavenger) confirmed that both the superoxide and H₂O₂ were requisites for stomatal closure. Co-localization of the superoxide and H₂O₂ in mitochondria and chloroplasts using fluorescent probes revealed that exposure to MV initially triggered higher superoxide and H₂O₂ generation in mitochondria. In contrast, MD elevated superoxide/H₂O₂ levels in chloroplasts. However, with prolonged exposure, MD and MV induced ROS production in other organelles. We conclude that ROS production in mitochondria and chloroplasts leads to stomatal closure. We propose that stomatal guard cells can be good models for examining inter-organellar interactions.

气孔保卫细胞的独特之处在于它们比叶绿体具有更多的线粒体。一些报告强调了线粒体作为气孔开放过程中主要能量来源的重要性。我们重新检查了它们在气孔关闭过程中的作用。气孔对甲萘醌（MD）和甲基紫精（MV）的显着敏感性表明线粒体和叶绿体都有助于促进拟南芥中的气孔关闭。与脱落酸 (ABA)（一种植物应激激素）一样，MD 和 MV 在微摩尔浓度下诱导气孔关闭。_{荧光探针 BES-So-AM 和 CM-H 2} DCFDA 分别表明，所有三种化合物均产生超氧化物和 H ₂ O ₂。钛试剂（一种超氧化物清除剂）和过氧化氢酶（一种H ₂ O ₂清除剂）的结果证实，超氧化物和H ₂ O ₂都是气孔关闭所必需的。使用荧光探针对线粒体和叶绿体中的超氧化物和 H ₂ O ₂进行共定位表明，暴露于 MV 最初会引发线粒体中更高的超氧化物和 H ₂ O ₂生成。相反，MD 提高了叶绿体中的超氧化物/H ₂ O ₂水平。然而，随着长时间暴露，MD 和 MV 会诱导其他细胞器产生 ROS。我们得出结论，线粒体和叶绿体中 ROS 的产生导致气孔关闭。我们认为气孔保卫细胞可以成为检查细胞器间相互作用的良好模型。