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A new type of cytoplasmic structure is described in the root tips of Allium cepa and several other genera. They are very probable composed of insoluble phosphate salts and as such can be demonstrated at the light and electron microscope level by conversion into its lead salt. They appear to be formed by coalescence of electron dense 'vesicles' which have granular phosphate deposits at their periphery. [ABSTRACT FROM AUTHOR]

The distribution of pyroantimonate-precipitable inorganic cation was studied in Allium cepa root tips using the direct potassium pyroantimonate fixation procedure. An accumulation of cation-antimonate precipitates was found at the boundary with the cell wall, presumably at the site of the plasmalemma; it extends to numerous infoldings at the cytoplasmic side suggesting a form of pinocytosis. A few large intramitochondrial antimonate deposits were also found and may reflect cation transport into mitochondria. The observed sites of inorganic cation accumulation in the nucleus apparently correlate with its RNA synthetic activity and reside mainly in the nucleolus. [ABSTRACT FROM AUTHOR]