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81.
Internodal elongation and orientation of cellulose microfibrils and microtubules in deepwater rice 总被引:4,自引:0,他引:4
Excised stem sections of deepwater rice (Oryza sativa L.) containing the highest internode were used to study the induction of rapid internodal elongation by gibberellin (GA). It has been shown before that this growth response is based on enhanced cell division in the intercalary meristem and on increased cell elongation. In both GA-treated and control stem sections, the basal 5-mm region of the highest internode grows at the fastest rate. During 24 h of GA treatment, the internodal elongation zone expands from 15 to 35 mm. Gibberellin does not promote elongation of internodes from which the intercalary meristem has been excised. The orientation of cellulose microfibrils (CMFs) is a determining factor in cell growth. Elongation is favored when CMFs are oriented transversely to the direction of growth while elongation is limited when CMFs are oriented in the oblique or longitudinal direction. The orientation of CMFs in parenchymal cells of GA-treated and control internodes is transverse throughout the internode, indicating that CMFs do not restrict elongation of these cells. Changes in CMF orientation were observed in epidermal cells, however. In the basal 5-mm zone of the internode, which includes the intercalary meristem, CMFs of the epidermal cell walls are transversely oriented in both GA-treated and control stem sections. In slowly growing control internodes, CMF orientation changes to the oblique as cells are displaced from this basal 5-mm zone to the region above it. In GA-treated rapidly growing internodes, the reorientation of CMFs from the transverse to the oblique is more gradual and extends over the 35-mm length of the elongation zone. The CMFs of older epidermal cells are obliquely oriented in control and GA-treated internodes. The orientation of the CMFs parallels that of the cortical microtubules. This is consistent with the hypothesis that cortical microtubules determine the direction of CMF deposition. We conclude that GA acts on cells that have transversely oriented CMFs but does not promote growth of cells whose CMFs are already obliquely oriented at the start of GA treatment. 相似文献
82.
83.
Sigrun Machemer-Röhnisch Richard Bräucker Hans Machemer 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1993,171(6):779-790
Summary In the statocystoid-bearing, flat ciliate Loxodes, the peculiar steady locomotion on submersed substrates (called gliding) was investigated between 1 g and 5.4 g under controlled environmental conditions in a centrifuge microscope. Videorecordings of the movements of large cell populations were processed with an automated analysis procedure. At 1 g, possible sedimentation was fully compensated, and vertical shifts of the population were neutralized because upward and downward orientations of the cells occurred at equal proportions (neutral gravitaxis). With rising gravity the resultant velocity of upward-gliding cells remained unchanged, whereas the velocity of downward-gliding cells increased continuously. Long-term exposure to hypergravity did not generate detectable signs of adaptation. The bipolar orientation of Loxodes persisted even under fivefold normal gravity, but the axis of orientation rotated from the gravity axis in the counterclockwise direction. The data suggest that both gravikinesis and graviorientation of gliding Loxodes are instrumental in perfect neutralization of sedimentation at terrestrial conditions. 相似文献
84.
85.
E. Jay DeRocher Francoise Quigley Regis Mache Hans J. Bohnert 《Molecular genetics and genomics : MGG》1993,239(3):450-462
The nucleotide sequences of the entire gene family, comprising six genes, that encodes the Rubisco small subunit (rbcS) multigene family in Mesembryanthemum crystallinum (common ice plant), were determined. Five of the genes are arranged in a tandem array spanning 20 kb, while the sixth gene is not closely linked to this array. The mature small subunit coding regions are highly conserved and encode four distinct polypeptides of equal lengths with up to five amino acid differences distinguishing individual genes. The transit peptide coding regions are more divergent in both amino acid sequence and length, encoding five distinct peptide sequences that range from 55 to 61 amino acids in length. Each of the genes has two introns located at conserved sites within the mature peptide-coding regions. The first introns are diverse in sequence and length ranging from 122 by to 1092 bp. Five of the six second introns are highly conserved in sequence and length. Two genes, rbcS-4 and rbcS-5, are identical at the nucleotide level starting from 121 by upstream of the ATG initiation codon to 9 by downstream of the stop codon including the sequences of both introns, indicating recent gene duplication and/or gene conversion. Functionally important regulatory elements identified in rbcS promoters of other species are absent from the upstream regions of all but one of the ice plant rbcS genes. Relative expression levels were determined for the rbcS genes and indicate that they are differentially expressed in leaves. 相似文献
86.
Cyclitol production in transgenic tobacco 总被引:11,自引:0,他引:11
Daniel M. Vernon Mitchell C. Tarczynski Richard G. Jensen Hans J. Bohnert 《The Plant journal : for cell and molecular biology》1993,4(1):199-205
High levels of cyclic sugar alcohols (cyclitols) correlate with tolerance to osmotic stress in a number of plant species. A gene encoding a cyclitol biosynthesis enzyme from a halophyte, Mesembryanthemum crystallinum has been introduced into tobacco. The gene, lmt1 , encodes a myo -inositol O -methyl transferase that, in M. crystallinum , catalyzes the first step in the stress-induced accumulation of the cyclitol pinitol. Tobacco transformed with the lmt1 cDNA under the control of the CaMV 35S promoter appeared phenotypically normal and exhibited IMT1 enzyme activity. Transformants accumulated a carbohydrate product not detectable in non-transformed control plants. This product was identified by HPLC and NMR as ononitol (1- d -4- O -methyl myo -inositol). Ononitol was a major carbohydrate constituent in leaf tissue of plants expressing the lmt1 gene, accumulating to up to 25% the level of sucrose in transformant seedlings. The identification of ononitol as the IMT1 product and the specific accumulation of this compound in transformed tobacco support a role for ononitol as a stable intermediate in pinitol biosynthesis and indicate that an epimerization activity lacking in tobacco is responsible for the conversion of ononitol to pinitol in M. crystallinum . The production of ononitol in tobacco indicates that plant carbohydrate metabolism is flexible and can accommodate the synthesis and accumulation of non-endogenous metabolites. The transgenic system described here will serve as a useful model to test the ability of cyclitols such as ononitol to confer tolerance to environmental stress in a normally glycophytic plant. 相似文献
87.
FINE STRUCTURAL ALTERATIONS IN CELL PARTICLES DURING CHEMICAL CARCINOGENESIS : III. Selective Action of Hepatic Carcinogens Other than 3'-Methyl-4-Dimethylaminoazobenzene on Different Types of Mitochondrial Swelling. Effect of Stimulated Liver Growth 总被引:1,自引:0,他引:1 下载免费PDF全文
The previous studies on the correlation between tumor incidence and changes in microsomal and mitochondrial swelling during feeding of 3'-methyl-4-dimethylaminoazobenzene to rats have been extended to other hepatic carcinogens. Administration of 4'-fluoro-4-dimethylaminoazobenzene, 4'-ethyl-2-methyl-4-dimethylaminoazobenzene, 2-acetylam-inofluorene, ethionine, and tannic acid were found to produce drastic alterations of the swelling of rat liver mitochondria. In contrast to these compounds, feeding of the non-carcinogenic azobenzene and 4-diethylaminoazobenzene produced only small changes in swelling. Significant modification in the over-all pattern of the swelling curve was observed when the usual concentration of 3'-methyl-4-dimethylaminoazobenzene was reduced, but not when the riboflavin level in the diet was increased tenfold. Feeding of high levels of this dye to the guinea pig did not affect mitochondrial swelling which is consistent with the resistance of this species to azo-dye carcinogenesis. Hypophysectomy provides protection against the alterations, produced by feeding 3'-methyl-4-dimethylaminoazobenzene, in the characteristics of thyroxine- or mercuric chloride-induced mitochondrial swelling. Studies with citric cycle substrates on mitochondrial swelling suggest block of the glutamate α-keto-glutarate pathway after feeding 3'-methyl-4-dimethylaminoazobenzene for 4 weeks. There is a considerable, but reversible, reduction of certain types of mitochondrial swelling in two situations associated with rapid liver growth: after partial hepatectomy and after intraperitoneal injection of 20-methylcholanthrene. Naphthacene, however, which also stimulates rapid liver growth, does not affect mitochondrial swelling. 相似文献
88.
Klassifikation der Prachtfinken, Spermestidae, auf Grund der Rachenzeichnungen ihrer Nestlinge 总被引:1,自引:0,他引:1
Hans Steiner 《Journal of Ornithology》1960,101(1-2):92-112
Ohne ZusammenfassungMotto: Mitunter gerät der Taxonom in ein Dilemma, worin ihm keine Nomenklatur-Regel zu Hilfe kommt.E. Stresemann, Vierteljahrsschr. Naturf. Ges. Zürich, Jahrg. 104, 1959, S. 213. 相似文献
89.
Hans Eberhard Fischer 《Genetica》1959,29(1):155-171
Ohne Zusammenfassungmit 6 AbbildungenHerrn Prof. Dr. R. Bauch zum 60. Geburtstag gewidmet. 相似文献
90.
Summary A thymus cyst was discovered in connection with autoradiographical studies on sulphur metabolism of the rat. The coincidence must be considered unique and has motivated amplifying histochemical investigations.The cyst-content showed a strong positive PAS-reaction and after toluidine blue -metachromasia, which along with the incorporation of S35 makes the presence of acid mucopolysaccharides likely. A strong blackening was noticed on the autoradiogram over the greater part of the cyst. This infers that the content has been metabolized here, in contradistinction to the centre with inactive colloid. 相似文献