Title: Spatial structure of mitochondria and ER denotes changes in cell physiology of cultured tobacco protoplasts
Abstract:The structure of mitochondria and of the endoplasmic reticulum (ER) in mesophyll protoplasts and regenerated cells was studied in vivo using the dye DiOC 6 (3) (3,3′‐dihexyloxacarbocyanine iodide) and...The structure of mitochondria and of the endoplasmic reticulum (ER) in mesophyll protoplasts and regenerated cells was studied in vivo using the dye DiOC 6 (3) (3,3′‐dihexyloxacarbocyanine iodide) and confocal laser scanning microscopy (CLSM). The relation to the cell’s physiology was investigated using a hormone‐based model system for elongation and division. The structure of the mitochondria and of their population depends on the status of the cell. In freshly isolated protoplasts small spherical mitochondria are clustered around the nucleus and the chloroplasts. During the first 4 days of culture they are transformed into long vermiform organelles which distribute evenly throughout the cytoplasm. In a medium containing only auxins, cells then enter a period of expansion. Their mitochondria retain the same structure but increase in quantity. In a medium with auxins and cytokinins cells start dividing. Their mitochondria typically become numerous and very small, and are distributed throughout the cytoplasm. Both types of organization were observed during weeks of ongoing expansion or division. The ER is always present as a network close to the cell membrane. In freshly isolated protoplasts a considerable part of the ER is clustered around the chloroplasts, the remaining part of the network has a reduced complexity and is partly broken. During subsequent protoplast culture the network grows into a complex web with fine meshes incorporating lots of plate‐like structures. This is the case in elongating cells as well as in dividing cells. Finally, the ER looks similar to the structure found in epidermal cells of the intact plant.Read More