Effects of subminimal temperature on physiology and ultrastructure of Zea mays embryo during germination

1983 ◽  
Vol 61 (4) ◽  
pp. 1117-1125 ◽  
Author(s):  
M. Crèvecoeur ◽  
R. Deltour ◽  
R. Bronchart
Keyword(s):  
Zea Mays ◽  
Cold Exposure ◽  
Ultrastructural Study ◽  
Organizer Region ◽  
Primary Root ◽  
Nucleolus Organizer Region ◽  
Nucleolus Organizer ◽  
Strong Decrease ◽  
Root Cells

The effects of a subminimal temperature on germinating Zea mays kernels have been studied at the physiological and ultrastructural levels. After 72 h of germination at 16 °C, kernels were exposed to 4 °C for intervals ranging from 4 to 25 days and then returned to 16 °C. Resumption of growth of all the embryos occurred when the cold exposure was 6 or 8 days. When periods at 4 °C were longer than 8 days, a decrease in the percentage of embryos able to grow was observed; this was proportional to the length of cold exposure. After 26 days or more at 4 °C, all the embryos died. An ultrastructural study of the primary root cells showed that modifications occur in the cytoplasm and in the nucleolus. The nucleolus became predominantly fibrillar and unusual ribonucleoproteinic granules [Formula: see text] were frequently observed in and near the nucleolus organizer region. These changes were related to a strong decrease in transcription.

Ultrastructural cytochemistry of the nucleus in Zea mays embryos during germination

1979 ◽  
Vol 40 (1) ◽  
pp. 43-62
Author(s):  
R. Deltour ◽  
A. Gautier ◽  
J. Fakan
Keyword(s):  
Zea Mays ◽  
Organizer Region ◽  
Great Part ◽  
Nucleolus Organizer Region ◽  
Nucleolus Organizer ◽  
Root Cells ◽  
Quiescent Cells ◽  
Closed Contact ◽  
Ultrathin Sections ◽  
Dense Chromatin

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.

The nucleolus organizer region of maize (Zea mays L.)

Chromosoma ◽  
1976 ◽  
Vol 57 (2) ◽  
pp. 103-117 ◽  
Author(s):  
Jean F. Givens ◽  
Ronald L. Phillips
Keyword(s):  
Zea Mays ◽  
Zea Mays L ◽  
Organizer Region ◽  
Nucleolus Organizer Region ◽  
Nucleolus Organizer

Mapping of the nucleolus organizer region on chromosome 4 inArabidopsis thaliana

1996 ◽  
Vol 250 (1) ◽  
pp. 123-128
Author(s):  
Georg Haberer ◽  
Thilo C. Fischer ◽  
Ramón A. Torres-Ruiz
Keyword(s):  
Organizer Region ◽  
Nucleolus Organizer Region ◽  
Nucleolus Organizer ◽  
Chromosome 4

Hybrid ape offspring of a mating of gibbon and siamang

Science ◽  
1979 ◽  
Vol 205 (4403) ◽  
pp. 308-310 ◽  
Author(s):  
RH Myers ◽  
DA Shafer
Keyword(s):  
Parental Species ◽  
Organizer Region ◽  
Nucleolus Organizer Region ◽  
Structural Rearrangement ◽  
Female Offspring ◽  
Nucleolus Organizer ◽  
Single Chromosome ◽  
Symphalangus Syndactylus ◽  
Hylobates Moloch ◽  
Lesser Apes

The serendipitous mating of a male gibbon, Hylobates moloch, and a female siamang, Symphalangus syndactylus, has produced two female offspring born 1 year apart. The hybrid karyotype of 47 chromosomes comprises the haploid complements of the parental species, 22 for the gibbon and 25 for the siamang. Chromosomal G and C banding comparisons revealed no clear homologies between the parental karyotypes except for the single chromosome in each species containing the nucleolus organizer region. The lack of homology suggests that the structural rearrangement of chromosomes has played a major role in the process of speciation for these lesser apes.

scholarly journals The relationship between position and expression of genes on the kangaroo X chromosome suggests a tissue-specific spread of inactivation from a single control site

1988 ◽  
Vol 51 (2) ◽  
pp. 103-109 ◽  
Author(s):  
Jennifer A. Marshall Graves ◽  
Garey W. Dawson
Keyword(s):  
Alternative Hypothesis ◽  
Organizer Region ◽  
Nucleolus Organizer Region ◽  
Control Site ◽  
Specific Pattern ◽  
Nucleolus Organizer ◽  
Tissue Specific ◽  
Expression Of Genes ◽  
Control Locus ◽  
The Relationship

SummaryIn marsupials, X chromosome inactivation is paternal and incomplete. The tissue-specific pattern of inactivation of X-linked loci (G6PD, PGK, GLA) has been attributed to a piecemeal inactivation of different regions of the X. We here propose an alternative hypothesis, in which inactivation of the marsupial X is a chromosome-wide event, but is differentially regulated in different tissues. This hypothesis was suggested by the relationship between the positions and activity of genes on the kangaroo paternal X. In the absence of an HPRT polymorphism, we have used somatic cell hybridization to assess the activity of the paternal HPRT allele in lymphocytes and fibroblasts. The absence of the paternal X, and of the paternal forms of G6PD or PGK, from 33 cell hybrids made by fusing HPRT-deficient rodent cells with lymphocytes or fibroblasts of heterozygous females, suggests that the HPRT gene on the paternal X is inactive in both tissues and therefore not selectable. Since HPRT is located medially on the Xq near GLA, which shares the same characteristics of activity, we suggest that the locus-specific and tissue-specific patterns of activity result from a differential spread of inactivation from a single control locus, located near HPRT and GLA, outwards in both directions to G6PD and PGK. The nucleolus organizer region on the short arm does not seem to be part of the inactivated unit.

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