Symbiotic dinitrogen fixation as affected by short-term application of nitrate to nodulatedPisum sativum L.

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 g_f.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 ^?-N_f.wt. in the nodule tissue. The results obtained indicate that the “photosynthate deprivation” reflects competition between assimilation of nitrate and fixation of dinitrogen.     

The Role of Endogenous Abscisic Acid in the Correlation Between the Cotyledon and Its Axillary Bud in PeaPisum sativum L

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.     

The cytotoxic and cytocidal effect of colicin E3 on mammalian tissue cells

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.     

The effect of ultrasound and its combination with radiation on the genetic material ofSaccharomyces cerevisiae

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.     

Relationship between acute and chronic exposures in mutagenicity studies in mice

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.     

Adiaspiromycosis in large free living carnivores

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.