scholarly journals THE EFFECT OF X-RAYS ON CHROMOSOMES IN DIFFERENT STAGES OF MEIOSIS

1935 ◽  
Vol 19 (1) ◽  
pp. 179-198 ◽  
Author(s):  
A. Marshak
Keyword(s):  
Linear Relationship ◽  
Meiotic Prophase ◽  
Sensitive Volume ◽  
X Rays ◽  
Homologous Pairing ◽  
Linkage Mechanism ◽  
Pollen Mother Cells ◽  
X Ray ◽  
Protein Molecules ◽  
Mother Cells

1. Pollen mother cells exposed to low dosages of x-rays at various stages show different frequencies of chromosome abnormalities in the first meiotic anaphase. 2. Maximum frequencies of abnormalities were obtained in buds irradiated in the pachytene stage of the meiotic prophase and in the preceding mitosis. 3. These results are taken to indicate that the x-ray-sensitive portions of the chromonemata are closely approximated in pairs in pachytene and in the early mitotic prophase. The significance of this in relation to non-homologous pairing is indicated. 4. From the nature of the chromosome configurations observed it is concluded that chromonemata are two-parted when they synapse and that a chromonematic division occurs between pachytene and anaphase and during the mitotic prophase. 5. The frequencies of abnormalities show a linear relationship to dosage. 6. The diameter of the sensitive volume of the chromonema is calculated and found to approximate the diameter of some known protein molecules. 7. The linkage mechanism is found to make up about 90 per cent of the total sensitive volume which corresponds with the approximate reduction in length of the chromonema from pachytene to anaphase. 8. The relation of these sensitive volumes to the gene is discussed.

scholarly journals Semi-automated protein crystal mounting device for the sulfur single-wavelength anomalous diffraction method

2010 ◽  
Vol 43 (2) ◽  
pp. 341-346 ◽  
Author(s):  
Yu Kitago ◽  
Nobuhisa Watanabe ◽  
Isao Tanaka
Keyword(s):  
Diffraction Method ◽  
Systematic Errors ◽  
Protein Crystal ◽  
X Rays ◽  
Anomalous Diffraction ◽  
X Ray ◽  
Frozen Solution ◽  
Custom Made ◽  
Protein Molecules ◽  
X Ray Absorption

Use of longer-wavelength X-rays has advantages for the detection of small anomalous signals from light atoms, such as sulfur, in protein molecules. However, the accuracy of the measured diffraction data decreases at longer wavelengths because of the greater X-ray absorption. The capillary-top mounting method (formerly the loopless mounting method) makes it possible to eliminate frozen solution around the protein crystal and reduces systematic errors in the evaluation of small anomalous differences. However, use of this method requires custom-made tools and a large amount of skill. Here, the development of a device that can freeze the protein crystal semi-automatically using the capillary-top mounting method is described. This device can pick up the protein crystal from the crystallization drop using a micro-manipulator, and further procedures, such as withdrawal of the solution around the crystal by suction and subsequent flash freezing of the protein crystal, are carried out automatically. This device makes it easy for structural biologists to use the capillary-top mounting method for sulfur single-wavelength anomalous diffraction phasing using longer-wavelength X-rays.

Developmental changes in DNA methylation of pollen mother cells of David lily during meiotic prophase I

2010 ◽  
Vol 44 (5) ◽  
pp. 754-759 ◽  
Author(s):  
Junjun Huang ◽  
Huahua Wang ◽  
Xiaojun Xie ◽  
Huanhuan Gao ◽  
Guangqin Guo
Keyword(s):  
Dna Methylation ◽  
Meiotic Prophase ◽  
Developmental Changes ◽  
Pollen Mother Cells ◽  
Prophase I ◽  
Meiotic Prophase I ◽  
Mother Cells

FINE STRUCTURE OF CHROMOSOME COILING AT MEIOTIC PROPHASE IN RHOEO DISCOLOR

1972 ◽  
Vol 14 (4) ◽  
pp. 801-808 ◽  
Author(s):  
Peter B. Moens
Keyword(s):  
Fine Structure ◽  
Nuclear Envelope ◽  
Meiotic Prophase ◽  
Synaptonemal Complexes ◽  
Pollen Mother Cells ◽  
Mother Cells

Most, if not all of the ends of synaptonemal complexes in Rhoeo discolor pollen mother cells are attached to the nuclear envelope. At least the first 4 μm of complex adjacent to the nuclear envelope is tightly coiled. Since each of the lateral elements is associated with one chromosome it means that the two homologues of the bivalent are relationally coiled in the distal segments.

scholarly journals THE KILLING OF COLON BACILLI BY ULTRAVIOLET LIGHT

1932 ◽  
Vol 15 (3) ◽  
pp. 351-361 ◽  
Author(s):  
Ralph W. G. Wyckoff
Keyword(s):  
Bacterial Population ◽  
Wave Length ◽  
Protein Molecule ◽  
Ultraviolet Region ◽  
Sensitive Volume ◽  
X Rays ◽  
Correct Description ◽  
X Ray ◽  
Single Protein ◽  
Straight Lines

The survival ratios of colon bacilli subjected to several monochromatic ultraviolet radiations follow semilogarithmic straight lines. For each wave length approximate observations have been made of the energy involved in cell destruction. This energy varies somewhat with frequency in the ultraviolet region; it is furthermore nearly one hundred times as great as the amount of X-ray energy required to bring about the same killing. Preliminary experiments show no measurable difference either in rate of killing or in lethal energy between B. coli and B. aertrycke. Parallel results have already been obtained with X-rays and electrons. The data from colon bacilli are interpreted in terms of the assumptions employed for X-rays. They indicate that though bacterial death should result from a single quantum absorption, millions more such absorptions seemingly are without injurious effect on cell growth and multiplication. The "sensitive volume" within which, according to this picture, the lethal quantum must be stopped proves to be about the same as that of a single protein molecule. If this is the correct description of the phenomena of ultraviolet killing, it seems strange that the millions of non-deadly quanta absorbed per bacillus should not show themselves by altered growth rates or in other ways. That they apparently do not suggests the inapplicability of the statistical picture. The death rate under this kind of radiation then would be primarily an expression of the relative sensitivities of the bacterial population. Additional experiments are required to determine this question.

scholarly journals Cytoplasniic differentiation during microsporogenesis in higher plants

2014 ◽  
Vol 50 (1-2) ◽  
pp. 3-12 ◽  
Author(s):  
H. Dichinnson
Keyword(s):  
Meiotic Prophase ◽  
Messenger Rna ◽  
Higher Plants ◽  
Pollen Mother Cells ◽  
Cytoplasmic Rna ◽  
Low Levels ◽  
Mother Cells ◽  
New Generation

Conspicuous cytoplasmic dedifferentiation in the pollen mother cells takes place early in the meiotic prophase of many plants. This event involves the removal of much of the cytoplasmic RNA. and the differentiation of both plastids and mitochondria to approaching the sole expression of their genomes. Much of the RNA removed from the cytoplasm passes to the nucleoplasm where it is utilised in the construction of a new `generation' of ribusomes. These new ribosomes are incorporated into cytoplasmic `nuclewhich disintegrate in the post-meiotic cytoplasm, restoring its ribosomes to pre-prophase levels. These changes are interpreted as evidence of a process by which the cytoplasm is cleansed of sporophytic control elements, both for the expression of the new gametophytic genome, and in the female cells of higher plants, for transmission to the new generation. The absence of control elements (presumably long-term messenger RNA) from the cytoplasm would result in the dedifferentiation observed in the organelles, and the low levels of reserves in these cells presumably results in characteristically lengthy and unusual redifferentiation of both plastids and mitochondria, once information-carrying molecules again enter the cytosol.

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