Abstract The endoplasmic reticulum (ER) forms contact sites with the chloroplast. Exposing contact sites that contain both the chloroplast and the ER to localised high‐fluence, wavelength specific, 405 nm violet light, hereinafter referred to as photostimulation, induces multiple, potentially interacting intra‐ and intercellular responses. The responses vary depending on the tissue type of the cell and the chloroplast. Photostimulating the ER‐chloroplast contact sites in growing epidermal cells of the hypocotyl of Arabidopsis thaliana , produces a wave of cytoplasmic ionic calcium that traverses the cell, spreading radially to other cells around the circumference of the hypocotyl. A transient ER stress accompanies the calcium wave. These responses occur in older epidermal cells (5–8 days post‐germination) with nonmotile chloroplasts tethered to the ER and the cell cortex but do not occur with motile or dividing chloroplasts. Dividing chloroplasts show a markedly different association with the ER, which forms a ring around the fission plane, similar to that of dividing mitochondria. Inhibition of calcium channels with lanthanum has no effect. Photostimulation of only the ER results in no ER stress and a calcium wave with a different spatiotemporal signature: delayed release and lower magnitude, with no accompanying ER stress response. Likewise, photostimulation of the chloroplast only, without the ER, produces no calcium wave or ER stress. General chloroplast photobleaching or restructuring caused by photostimulation is not the cause of this response; photostimulation with 488 nm of the same intensity and power as 405 nm photostimulation produces no change in cytosolic calcium levels. The pH of the ER decreases, indicating the involvement of ER ion transporters in the response. A wave of increased reactive oxygen species (ROS) in mitochondria and nuclei accompanies photostimulation. Together, these data support a model by which tethered ER‐chloroplast contact sites constitute a unique subcellular photosensitive region and are part of an ER‐mediated signalling network. Lay Abstract: The endoplasmic reticulum (ER) forms contact sites with the chloroplast. Shining violet (405 nm) light on the chloroplast with its associated ER produces a calcium wave through the cell that is communicated to other cells. This is correlated with a wave of transient denaturation of the luminal proteins of the ER (ER stress) and increased reactive oxygen species (ROS) in mitochondria. The wavelength dependence and precise cellular location of the light stimulation implies a novel way for plants to sense light. The movement of the response through the cell is consistent with the mediation of the response by a subcellular network, such as that formed by the ER.

Sara N. Maynard

Lawrence R. Griffing

Journal of Microscopy

《显微镜杂志》是致力于显微镜科学的最古老的期刊，也是皇家显微镜学会唯一经同行评审的出版物。它发表的论文报告了显微镜技术的最新发展，例如显微镜技术的进步或新的应用领域。该杂志不寻求发表显微镜或标本制备的常规应用，即使提交的材料可能具有很高的科学价值。范围涵盖物理和生物科学的研究，并涵盖使用光、电子、X 射线和其他方法的成像方法辐射以及原子力和近场技术。欢迎跨学科研究。与显微镜有关的论文也很受欢迎，涉及光学理论、光谱学、新的标本制备和操作方法以及图像记录、处理和分析，包括活体标本的动态分析。出版类型包括全文、热门话题快速通信和评论文章。考虑提交评论文章的作者应首先联系编辑部。

The Journal of Microscopy is the oldest journal dedicated to the science of microscopy and is the only peer-reviewed publication of the Royal Microscopical Society. It publishes papers reporting the latest developments in microscopy techniques, including advancements in microscopy technology and new areas of application. While the journal does not seek to publish routine applications of microscopy or specimen preparation, submissions with high scientific value will be considered. The scope encompasses research in both physical and biological sciences, covering imaging methods using light, electron, X-ray, and other radiation techniques, as well as atomic force and near-field techniques. Interdisciplinary research is also welcomed. Papers related to microscopy, particularly those involving optical theory, spectroscopy, new specimen preparation and operational methods, as well as image recording, processing, and analysis (including dynamic analysis of live specimens), are highly encouraged. Publication types include full articles, rapid communications on hot topics, and review articles. Authors considering submitting review articles should first contact the editorial office.

《Journal of Microscopy》是显微镜科学领域最古老的期刊，也是皇家显微镜学会唯一经过同行评审的出版物。该期刊发表关于显微镜技术最新发展的论文，包括显微镜技术的进步和新的应用领域。虽然该杂志不寻求发表显微镜或标本制备的常规应用，但即使提交的材料具有很高的科学价值，也会受到审查。期刊的范围涵盖物理和生物科学的研究，涉及使用光学、电子、X 射线及其他成像方法的辐射，以及原子力和近场技术。跨学科研究也受到欢迎。与显微镜相关的论文，尤其是涉及光学理论、光谱学、新的标本制备和操作方法，以及图像记录、处理和分析（包括活体标本的动态分析）也很受欢迎。出版类型包括全文、热门话题快速通信和评论文章。考虑提交评论文章的作者应首先联系编辑部。

Category	Quartile
工程技术	4
工程技术, 显微镜技术	4

The photosensitive endoplasmic reticulum‐chloroplast contact site

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