A cytochemical approach to the lipid composition of mitochondrial matrix granules in brown adipose tissue and liver

Do mitochondria in Dendrobium petal mesophyll cells form vacuole-like vesicles?

Using transmission electron microscopy, we investigated the ultrastructure of mitochondria in petal mesophyll cells of the orchid Dendrobium cv. Lucky Duan, from the time of floral opening to visible petal senescence. Cells close to the vascular bundle contained many mitochondria, some of which showed internal degeneration. This inner mitochondrial breakdown was accompanied by an eightfold increase in mitochondrial volume. Small electron-dense granules (approximately 0.04 mum in diameter) at the periphery of the mitochondrial matrix remained. These granules were used as an indicator of still later stages of mitochondrial development in these cells. The apparent final stage of mitochondrial degeneration was a single-membrane-bound vesicle, resembling a vacuole. No evidence was found for the idea that mitochondria became transferred (intact or degenerated) into a lytic vacuole. Taken together, the data suggest the hypotheses that (a) mitochondria in cells close to the vascular bundle in petals of open Dendrobium cv. Lucky Duan flowers undergo large-scale internal degeneration and that (b) such degenerating mitochondria form vacuole-like vesicles.

Mitochondrial matrix granules: their behavior during changing metabolic situations and their relationship to contact sites between inner and outer mitochondrial membranes

Since their discovery in the early fifties mitochondrial granules have been the subject of many researches. Some twenty years ago two hypotheses on their function were introduced. Peachey thought that the granules were a sink of cations and that they would eventually regulate the concentrations of these ions. Alternatively, Barnard thought that the granules were precursors of the mitochondrial inner membrane. There are only a few data on organic constituents of the granules. Phospholipids (e.g., cardiolipin) glycoprotein or lipids, calcium precipitable lipoprotein, cytochrome c oxidase seem to be present in the granules. There has been much debate on whether calcium is present or not. Reports are mostly based on X-ray microanalysis, the result of which depends on preparation techniques. In heart muscle in stimulating situations the NMG (native matrix granules) move towards the inner membrane and are incorporated in it. They appear to create contact sites between inner and outer mitochondrial membranes in which enzymes can function efficiently. It is hypothetized that the system, NMG-contact sites, forms the structural basis of a regulatory mechanism, by which cells can cope with a high and sudden energy demand.

Immunocytochemical investigation of native matrix granules of the rat heart mitochondrion

We have examined the ultrastructure and the protein content of native matrix granules (NMG) in rat heart mitochondria, by postembedding immunocytochemistry. Cytochrome c oxidase was found to be present in these granules. It is believed that these granules contain incomplete inner mitochondrial membrane fractions, which can be incorporated in the membrane after stimulation of the metabolism.

Intramitochondrial inclusions in the kidney of the pygmy mouse

Intramitochondrial inclusions averaging 1000 A in diameter were observed in the cells of the proximal convoluted tubules in samples of kidneys from pygmy mice, Baiomys taylori. Electron microscopic study of unstained sections and mitochondrial fractions showed that these inclusions are lipid and found at a S.G. 1.37 in a linear sucrose gradient. Renal glycogen, inorganic phosphate and plasma sodium were significantly higher in the pygmy mouse and plasma calcium was lower, as compared with the laboratory mouse. We believe these intramitochondrial inclusions to be lipid which accumulates divalent cations, particularly calcium, which acts as a sodium pump allowing the pygmy mouse to conserve water and adapt to its environment.

X-ray microanalysis of epon sections after oxygen plasma microincineration

Dark-gold sections of osmium tetroxide-fixed, Epon-embedded brown adipose tissue before and after low-temperature oxygen plasma microincineration were examined using a high-resolution scanning transmission electron microscope and an energy-dispersive X-ray spectrometer. Microincineration produced ash patterns which were free of organic matrix, chlorine (from the Epon) and probably osmium (from the fixative). X-ray sensitivity was improved by a factor of 2-4 owing to decreased background, and sulphur, calcium and probably phosphorus were detected in the ash. Fidelity of the ash patterns permitted microanalytical spatial resolution of 0.1 micrometer or better. Oxygen plasma microincineration is thus shown to offer advantages for high resolution X-ray microanalysis of conventionally sectioned biological material. Its future application to shock-frozen, frozen-dried, unstained sections is indicated.

Electron microscopic study on the lipid content of intramitochondrial granules in proximal convoluted tubule of guinea pig kidney and their ability to accumulate calcium ions

The intramitochondrial dense granules of the kidney proximal tubule fixed with OsO4 are osmiophilic since they are bleached by H2O2 treatment and they disappear after glutaraldehyde fixation alone. Following ethanol extraction and subsequent osmification these granules become invisible but pure aceton treatment does not greatly alter their osmiophilia. The findings suggests that the osmiophilic intramitochondrial granules are rich in phospholipids. When the kidney cortex is incubated in the presence of calcium of acetate, calcium accumulates on the intramitochondrial granules increasing their size and number. The intramitochondrial granules are found more frequently in tissues where the transport of water or ions is big. They contribute to the sodium transport (RIEDEL, BUCHER and ERKOCAK 1968). They are composed mainly of neutral lipids (SANZONE, SWARTZENDRUBER and SNYDER 1970) and phospholipids (WENDEL and BARNARD 1974). They are formed by the precipitation of calcium and other ions (GREENAWALT, ROSSI and LEHNINGER 1964; Peachey 1964). in this present work the structure of dense intramitochondrial granules has been studied regarding electron opaque materials. This way on one hand the lipids and the nucleic acids have been investigated, on the other hand the intramitochondrial granules have been loaded with calcium, a cation showing density in precipitated form and found in great amount into the cell.