Plastid tubules of higher plants are tissue-specific and developmentally regulated

Green fluorescent stroma filled tubules (stromules) emanating from the plas tid surface were observed in transgenic plants containing plastid-localized green fluorescent protein (GFP), These transgenic tobacco plants were furt her investigated by epifluorescence and confocal laser scanning microscopy (CSLM) to identify developmental and/or cell type specific differences in t he abundance and appearance of stromules and of plastids, Stromules are rar ely seen on chlorophyll-containing plastids in cell types such as trichomes , guard cells or mesophyll cells of leaves. In contrast, they are abundant in tissues that contain chlorophyll-free plastids, such as petal and root. The morphology of plastids in roots and petals is highly dynamic, and plast ids are often elongated and irregular. The shapes, size, and position of pl astids vary in particular developmental zones of the root. Furthermore, sus pension cells of tobacco exhibit stromules on virtually every plastid with two major forms of appearance, The majority of cells show a novel striking 'octopus- or millipede-like' structure with plastid bodies clustered around the nucleus and with long thin stromules of up to at least 40 mu m length stretching into distant areas of the cell. The remaining cells have plastid bodies distributed throughout the cell with short stromules. Photobleachin g experiments indicated that GFP can flow through stromules and that the te chnique can be used to distinguish interconnected plastids from independent plastids.