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R Deltour

Publications and source records attributed to R Deltour.

30 records · Page 2Linked to original sources
PubMed1981

Inorganic phosphate accumulation and phosphatase activity in the nucleus of maize embryo root cells.

The nucleus of growing root cells Zea mays contains a high concentration of inorganic phosphate. In order to verify whether this high nuclear Pi concentration is correlated with the metabolic activity of the nucleus, the Pi has been visualized in root cells of maize embryos at the electron-microscope level during 2 different periods which are both characterized by a spectacular reactivation of the nuclear metabolism, i.e. the early germination and the period of recovery following a thermal treatment given to the seeds after 48 h of germination. In both situations the Pi concentration increased in the nucleus during its reactivation. To verify whether the high nuclear Pi concentration could be of endogenous origin, the phosphatase activities were measured in crude extracts of root tissues during nuclear reactivation. The specific activity was optimal at pH 4.5 and was shown to increase with cellular reactivation. The ultrastructural localization of acid phosphatase activity showed that Pi may be produced at 3 distinct sites: plasmalemma, vacuoles and most probably nucleus itself. High acid phosphatase activities were found in nuclei displaying a high metabolism. Taking these results and previous data into account, we suggest that a correlation may exist between the rate of nuclear transcription, the level of nuclear acid phosphatase activity and the nuclear Pi accumulation.

Acid Phosphatase↗
PubMed1981

Organization of transcribed and nontranscribed chromatin in isolated nuclei of Zea mays root cells.

A slightly modified technique of Miller was applied to nuclei isolated from roots of germinating corn embryos. Under the conditions used, the extranucleolar chromatin was easily spread but the nucleolar chromatin often remained aggregated. The nontranscribed chromatin regions consisted of long deoxyribonucleoprotein (DNP) fibrils with the typical "beads-on-a-string" appearance of nucleosomal arrangement. When the EDTA concentration of the spreading medium was increased, linear arrangement of nucleosomes, 20 nm and 40-50 nm DNP granules were observed on the same DNP fibril. The supranucleosomal granules were also closely packed without any apparent order. Independently of the EDTA concentration, numerous non-nucleolar ribonucleoprotein (RNP) fibrils with a knobby structure were seen laterally bound to DNP fibrils. These knobby RNP fibrils (transcripts) were highly folded and appeared in "bunch-of-grapes" configurations. Each RNP knob measured 23 nm in diameter and the longest of these RNP fibrils were estimated to reach 1.5 micron. The RNP fibrils were often solitary and never exceeded 8 per 10 micron of the DNP axis. Distribution, morphology, and size of these transcripts distinguished them from the nucleolar "Christmas-tree"-like figures, which were rarely observed with our material. These non-nucleolar transcriptional units may correspond to genes coding for the heterodisperse nuclear RNA (hnRNA) and the knobs of 23 nm could be related to informofers or hnRNA particles. Up to now, the visualization of transcriptional units for higher plant tissues have never been reported.

Chromatin↗
PubMed1979

Ultrastructural cytochemistry of the nucleus in Zea mays embryos during germination.

The ultrastructure of embryonic root cells of Zea mays was studied from the quiescent stage (dry seed) to 72 h of germination. Semithin and ultrathin sections of tissues fixed with only glutaraldehyde and embedded in Epon were observed after usual section staining and after cytochemical reactions specific for DNA or preferential for ribonucleoproteiNS. In quiescent cells, dense chromatin forms a network which fills a great part of the nucleoplasm. Following germination, gradual dispersion of chromatin occurs: total dispersion is reached at 24 h. After 48 h the chromatin appears moderately condensed again. The nucleolus is compact and predominately fibrillar in dry cells. At 48 h a typical pars granulosa is differentiated. At 8 h a pronounced vacuolation of the nucleolus is observed; nucleolar vacuoles persist until 72 h but become less numerous. During the first 8 h of germination a nucleolus organizer region (NOR) in an eccentric position is associated with the nucleolus; by 24 h and later this NOR has disappeared. No DNA can be visualized in the nucleolar matrix between 0 and 8 h of germination, whereas later, when the nucleolus is reactivated. DNA is always detected in the nucleolar matrix and vacuoles. During the first 72 h of germination, heavily contrasted areas, rich in ribonucleoproteins and appearing to be fibrillar texture, are found in the nucleoplasm, often in closed contact with the dense chromatin. In quiescent cells dense ribonucleoprotein granules, approximately 40 nm in diameter are found dispersed or clustered in the nucleoplasm; after 8 h larger (50 nm), dense ribonucleoprotein granules are found frequently clustered in granular areas in the extranucleolar space. At 8 h of germination, when the nucleolus is temporarily highly vacuolated, unusual 35-nm ribonucleoprotein granules are found both in the smallest vacuoles and on the periphery of the nucleolus.

Cell Nucleolus↗
PubMed1976

Phosphatase of Chlamydomonas reinhardi: biochemical and cytochemical approach with specific mutants.

The unicellular alga Chlamydomonas reinhardi produces two constitutive acid phosphatases and three depressible phosphatases (a neutral and two alkaline ones) that can utilize napthyl phosphate as a substrate. Specific mutants depressible phosphatase were used to investigate biochemical properties and the cytochemical localization of these enzymes. The two constitutive phosphatases show similar pH optima (about 5.0) and Km values (2 x 10(-3) to 3.3 x 10(-3) M) but differ in their heat sensitivity and affinity for glycerophosphate.

Acid Phosphatase↗
PubMed1975

Changes in phosphatase activity associated with cell wall defects in Chlamydomonas reinhardi.

Experiments were performed to isolate mutants lacking alkaline phosphatase in Chlamydomonas reinhardi. Mutants with null enzyme activity were obtained. A cytological study of these mutants however revealed cell wall defects, suggesting that the loss of phosphatase activity in these strains is not due to the inactivation of the corresponding phosphatase structural gene but rather to the leakage of this enzyme as a consequence of the cell wall abnormality. Incidentally, this finding provides the basis of a convenient method for selecting easily cell wall mutants of Chlamydomonas.

Alkaline Phosphatase↗