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31.
Metabolism of activated oxygen in detached wheat and rye leaves and its relevance to the initiation of senescence 总被引:11,自引:0,他引:11
Pollen grains of Plumbago zeylanica L. were serially sectioned and examined using transmission electron microscopy to determine the three-dimensional organization of sperm cells within the microgametophyte and the quantity of membrane-bound organelles occurring within each cell. Sperm cells occur in pairs within each pollen grain, but are dimorphic, differing in size, morphology and organelle content. The larger of the two sperm cells (Svn) is distinguished by the presence of a long (approx. 30 m) projection, which wraps around and lies within embayments of the vegetative nucleus. This cell contains numerous mitochondria, up to two plastids and, infrequently, microbodies. It is characterized by a larger volume and surface area and contains a larger nucleus than the other sperm cell. The second sperm cell (Sua) is linked by plasmodesmata with the Svn, but is unassociated with the vegetative nucleus. It is smaller and lacks a cellular projection. The Sua contains relatively few mitochondria, but numerous (up to 46) plastids and more microbodies than the other sperm. The degree of dimorphism in their content of heritable cytoplasmic organelles must at fertilization result in nearly unidirectional transmission of sperm plastids into just one of the two female reproductive cells, and preferential transmission of sperm mitochondria into the other.Abbreviations Sua
sperm cell unassociated with the vegetative nucleus
- Svn
sperm cell physically associated with the vegetative nucleus
1=Russell and Cass (1981) 相似文献
32.
Among diploid Lathyrus species a threefold variation in nuclear DNA amount is attributable to differences in the amount of repetitive DNA. Cross reassociation among repetitive and among non-repetitive DNA fractions from different species shows substantial divergence in DNA composition. The divergence in base composition is correlated with nuclear DNA amount. The degree of divergence is of the same order of magnitude in both the repetitive and nonrepetitive fractions. 相似文献
33.
Naturally occurring antigenic variants of visna virus isolated from two persistently infected sheep have been compared using RNAase T1 fingerprint analysis of the viral RNAs. All the viruses examined have oligonucleotide changes in the 3′-terminal region of the viral genome and many of the alterations are common among the variants of both sheep. There is progressive accumulation of point mutations in the 3′-terminal region of antigenically altered viruses isolated from persistently infected animals. In addition, antigenic variants isolated independently from another sheep contain the same altered oligonucleotides; the nucleotide sequences of these oligonucleotides are identical. These data strongly suggest that the alterations observed in the nucleotide sequence of the variants are related to the change in their antigenic character. 相似文献
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J. T. P. Albrechtová J. Ullmann J. Krekule A. Blažková I. Machžčková Z. Vondráková J. Blažková S. Procházka V. Borkovec D. A. Baker F. Didehvar Z. Tesařová V. Czaková M. Zima K. Doležal T. Doleželová V. Psota M. Dundelová V. Reinöhl S. Prochàzka J. Mikulík M. Dvořěk J. Černohorskě O. Auxtová B. Cholvadová D. Lišková M. Kubačková S. Karácsonyi L. Bilisics 《Biologia Plantarum》1992,34(1):569-587
37.
Thirty-nine enterotoxigenic cultures of Clostridium perfringens type A were studied for enterotoxin and haemagglutinin production. Enterotoxin was quantitated by sandwich ELISA and DOT-ELISA techniques and haemagglutinin titres were determined using sheep and human erythrocytes. Haemagglutinins from only six cultures reacted against both sheep and human erythrocytes; a further 13 reacted only against human erythrocytes, and another five only against sheep cells.The authors are with the Department of Veterinary Public Health and Epidemiology, Ranchi Veterinary College, Birsa Agricultural University, Ranchi-834007 (Bihar), India. 相似文献
38.
Buoyant density gradient analysis of nuclear DNA of fourCucumis species showed asymmetric profiles indicating the presence of satellite DNA sequences in the nuclear genome. A highly repeated satellite DNA sequence was isolated from the nuclear genome ofC. metuliferus under neutral CsCl gradients. The satellite DNA constitutes about 4.96% of total nuclear DNA and has 48.06% guanine plus cytosine content. The kinetic complexity of satellite DNA is 150 times smaller than T4 phage DNA and the base sequence divergence is low.3H-labeled cRNA transcribed from satellite DNA hybridized clearly to six heterochromatic knobs of pachytene chromosomes. The knob heterochromatin can be distinguished by Giemsa C-banding of pachytene chromosomes. Restriction enzyme analysis and Southern blot hybridization indicated that the satellite DNA has a tandem arrangement and predominantly formed two bands of size 210 and 151 base pairs. Absence of knob satellite DNA ofC. metuliferus in the nuclear genomes ofC. melo, C. anguria andC. sativus showed thatC. metuliferus remains isolated within the genusCucumis. 相似文献
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Summary Nutritional requirements for the production of ergot alkaloids were studied with Aspergillus fumigatus under submerged conditions of fermentation, in a chemically defined medium. Glucose in combination with mannitol and triammonium citrate were found to be the best sources of carbon and nitrogen for the production of alkaloids. Carbon to nitrogen ratio of 4.16 : 1 was found optimum. Phosphate at elevated concentration inhibited alkaloid production. 相似文献
40.