No abstract

Plant mitochondria move dynamically inside cells and this movement is classified into two types: directional movement, in which mitochondria travel long distances, and wiggling, in which mitochondria travel short distances. However, the underlying mechanisms and roles of both types of mitochondrial movement, especially wiggling, remain to be determined. Here, we used confocal laser-scanning microscopy to quantitatively characterize mitochondrial movement (rate and trajectory) in Arabidopsis thaliana mesophyll cells. Directional movement leading to long-distance migration occurred at high speed with a low angle-change rate, whereas wiggling leading to short-distance migration occurred at low speed with a high angle-change rate. The mean square displacement (MSD) analysis could separate these two movements. Directional movement was dependent on filamentous actin (F-actin), whereas mitochondrial wiggling was not, but slightly influenced by F-actin. In mesophyll cells, mitochondria could migrate by wiggling, and most of these mitochondria associated with chloroplasts. Thus, mitochondria migrate via F-actin-independent wiggling under the influence of F-actin during their association with chloroplasts in Arabidopsis.

Different organelles function coordinately in numerous intracellular processes. Photorespiration incidental to photosynthetic carbon fixation is organized across three subcellular compartments: chloroplasts, peroxisomes, and mitochondria. Under light conditions, these three organelles often form a ternary organellar complex in close proximity, suggesting a connection with metabolism during photorespiration. However, due to the heterogeneity of intercellular organelle localization and morphology, organelles' responses to changes in the external environment remain poorly understood. Here we used array tomography by field emission scanning electron microscopy to image organelles inside the whole plant cell at nanometer resolution, generating a three-dimensional (3D) spatial map of the light-dependent positioning of chloroplasts, peroxisomes, nuclei, and vacuoles. Our results show, in light-treated cells, the volume of peroxisomes increased, and mitochondria were simplified. In addition, the population of free organelles decreased, and the ternary complex centered on chloroplasts increased. Moreover, our results emphasized the expansion of the proximity area rather than the increase in the number of proximity sites inter-organelles. All of these phenomena were quantified for the first time on the basis of nanoscale spatial maps. In summary, we provide the first 3D reconstruction of Arabidopsis mesophyll cells, together with nanoscale quantified organelle morphology and their positioning via proximity areas, and then evidence of their light-dependent changes.

Abstract:We propose ultra-high resolution optical coherence tomography to study the morphological development of internal organs in medaka fish in the post-embryonic stages at micrometer resolution. Different stages of Japanese medaka were imaged after hatching in vivo with an axial resolution of 2.8 µm in tissue. Various morphological structures and organs identified in the OCT images were then compared with the histology. Due to the medaka's close resemblance to vertebrates, including humans, these morphological features play an important role in morphogenesis and can be used to study diseases that also occur in humans. References and links1. J. Wittbrodt, A. Shima, and M. Schartl, "Medaka--a model organism from the far East," Nat. Rev. Genet. 3(1), 53-64 (2002). 2. T. Iwamatsu, "Stages of normal development in the medaka Oryzias latipes," Mech. Dev. 121(7-8), 605-618 (2004). 3. T. Iwamatsu, "Growth of the Medaka (I)-Formation of Vertebrae, Changes in Blood Circulation, and Changes in Digestive Organs," Bull. Aichi Univ. Educ. 61, 55-63 (2012). 4. J. Finn, M. Hui, V. Li, V. Lorenzi, N. de la Paz, S. H. Cheng, L. Lai-Chan, and D. Schlenk, "Effects of propranolol on heart rate and development in Japanese medaka (Oryzias latipes) and zebrafish (Danio rerio)," Aquat. Toxicol. 122-123, 214-221 (2012). 5. M. Islinger, D. Willimski, A. Völkl, and T. Braunbeck, "Effects of 17a-ethinylestradiol on the expression of three estrogen-responsive genes and cellular ultrastructure of liver and testes in male zebrafish," Aquat. Toxicol. 62(2), 85-103 (2003). 6. J. Zha and Z. Wang, "Assessing technological feasibility for wastewater reclamation based on early life stage toxicity of Japanese medaka (Oryzias latipes)," Agric. Ecosyst. Environ. 107(2-3), 187-198 (2005). 7. C. Cubbage and P. Mabee, "Development of the cranium and paired fins in the zebrafish Danio rerio (Ostariophysi, Cyprinidae)," J. Morphol. 229(2), 121-160 (1996). and their relation to neuromeres and migration (secondary matrix) zones,"