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101.
Effect of nitrate on the nitrogenase (C2H2-reduction) activity, growth of nodule tissue accumulation of nitrate and nitrate reductase activity in 4-weeks-old nodulated peas (Pisum sativum l.) was investigated. A relatively slow decrease of the total nitrogenase activity (μmol C2H4 per root per h), as compared with plants cultivated without nitrate, was due to both retardation of further growth of the nodule tissue and to a decrease of their specific nitrogenase activity (μmol C2H4 per gf.wt. per h). However, an absolute and pronounced decrease of both nitrogenase activities occurred only 4 or 7 d after the application of nitrate. The addition of nitrate led to its rapid accumulation in the nodule and leaf tissue with a simultaneous induction of the nitrate reductase activity. The nitrogenase activity was not completely inhibited even after a 7-d cultivation with 280 ppm NO3 ?-N in the nutrient medium and after accumulation of up to 180 ppm NO3 ?-Nf.wt. in the nodule tissue. The results obtained indicate that the “photosynthate deprivation” reflects competition between assimilation of nitrate and fixation of dinitrogen. 相似文献
102.
103.
104.
On cutting off one cotyledon from decapitated pea seedlings cultivated in the dark, the apical dominance is restored, as is well-known, by the growth of the bud of the removed cotyledon. As early as 12 h following cotyledon amputation(i.e. at the time when buds of both cotyledons-remaining and removed-are not yet differentiated in size), a decrease in the level of endogenous abscisic acid can be demonstrated in the bud of the removed cotyledon. 相似文献
105.
The plasma membrane of mammalian cells can mediate the cytotoxic and cytocidal effects of colicin E3. As little as 102 lethal units of purified colicin E3 per cell exert a pronounced cytocidal effect on human epithelial HeLa cells and as little
as 104 lethal units per cell also on line L mouse fibroblasts in tissue culture. Cells in complete monolayers are rapidly killed,
become spherical and shrink, they are detached from the support and finally autolyzed. The percentage of killed cells in both
lines is directly proportional to the multiplicity of colicin used. Theld
50 for HeLa cells is about 30 times lower than for L cells. At the multiplicity of 105 l.u., usually 100 % HeLa cells and 90 % L cells are killed in 2–3 days. Purified colicins E2 and D have no demonstrable cytological
effect on HeLa cells, although DNA synthesis in L cells appears to be partly inhibited by colicin E2. The profound effect
of colicin E3 on mammalian cells could be interpreted in a similar way as in bacteria,viz. as a specific cleavage of rRNA. 相似文献
106.
Ultrasonication at 20 kHz, intensity 35 W/cm2 and amplitude 15–25 μm of a diploid strain ofSaccharomyces cerevisiae was found to act as a weak mutagen with maximum efficiency at the 20 % survival of the cells. Under these conditions, the
frequency of reversion of the suppressible allele ilv1-92 increased ten times, the frequency of mitotic gene conversion four
times. Doses leading to survivals lower than 20 % led to a slight increase in the frequency of cytoplasmic respiration-deficient
mutants. Submutagenic doses applied immediately after γradiation or UV light did not substantially increase the effect of
these physical agents on the genetic material of the yeast strain investigated. Application of ultrasound prior to UV radiation
did not considerably influence the effect of the radiation either. 相似文献
107.
R.J. Šrám 《Mutation research》1976,41(1):25-42
The relationship between acute and chronic exposures in mutagenicity studies on mammals still lacks experimental data that might permit the decision whether or not the long-term exposures are of significance in mutagenicity testing.Fractional application of TEPA, THIOTEPA, EMS cyclophosphamide and sodium arsenite was made in experiments with mice, by using the dominant-lethal test and cytogenetic analysis of bone marrow. In most experiments the repeated application yielded the same or higher genetic injury than the same total dose at a single application. Negative results are discussed in relation to the threshold dose and the different sensitivity of the germ-cell stage.Possible interaction of mutagens was also studied by analyzing the combined effect of a long-term exposure to sodium arsenite, which probably affected the repair mechanism, and of a single dose of TEPA. It is concluded that the present stage of knowledge requires acceptance of the opinion that the genetic risk induced by chronic exposure to a chemical is as serious as that induced by an acute exposure. 相似文献
108.
Adiaspiromycosis was identified in 6 animals in the examination of the lungs of 90 large carnivores. Emmonsia crescens (Chrysosporium parvum var. crescens) was demonstrated as the causative agent in 5 cases of disease — in the badger (Meles meles), the otter (Lutra lutra) and the fox (Vulpes vulpes). E. parva was demonstrated in the remaining case of disease in a fox. The badger is a new, up to the present unknown host of E. crescens. The sporadic occurrence of adiaspiromycosis in the fox and the otter classifies this disease among rare diseases of these animals. 相似文献
109.
J. Šebánek 《Biologia Plantarum》1976,18(4):307-310
The role of exogenously supplied gibberellin (GA3) and cytokinin (benzyladenin -BA) in the correlation between the mature leaf and its axillary bud was investigated in one-node segments ofHydrangea. When both leaves were left on the segments, then both GA and BA were able to determine the dominance between axillary buds, that means that the bud treated with the corresponding growth regulator grew more vigorously. When one of the leaves was removed, the bud belonging to the removed leaf grew more vigorously, but GA applied onto the axillary bud belonging to the remaining leaf caused a complete correlation reversal: the bud belonging to the remaining leaf grew more vigorously. On the contrary, the application of BA onto the bud of the remaining leaf resulted in only insignificantly stimulated growth of the bud belonging to this leaf. 相似文献
110.
Summary Intact and denervated extensor digitorum longus (EDL) muscles of 20-day-old inbred Lewis-Wistar rats were labelled with 3H-thymidine. Ninety minutes after the injection of the isotope 4.0% of the nuclei were labelled in the intact (i.e. innervated) and 9.6% in the muscles, denervated 3 days before administration of the isotope. The labelled EDL muscles were grafted into the bed of the previously removed EDL muscles of inbred animals and these isografts were studied 30 days later.In the EDL muscles, regenerated from innervated isografts only occasionally labelled endothelial cells were found whereas in the muscles regenerated from denervated isografts also parenchymal muscle nuclei were regularly labelled. The incidence of labelled nuclei in the regenerated EDL muscles was, however, about 20 times lower than in the donor EDL muscles. The present experiments provide a direct proof of utilization of donor satellite cell nuclei for regeneration in grafted muscle tissue. With respect to the low incidence of labelled nuclei in regenerated EDL muscles, other sources of cells apparently also contribute to the regeneration process. 相似文献