Humic acids inhibit the formation but not the mutagenicity of N-methyl-N-nitrosourea

Humic acids in the form of potassium humate (KH), at concentrations exerting a strong inhibitory effect on the formation of N-methyl-N-nitrosourea (MNU) when present during the nitrosation of N-methylurea (MU) at pH 3, did not reduce the mutagenicity of preformed MNU in Tradescantia, clone 4430. The inhibitory effect of 20 mg/ml KH corresponds approximately to that of 3.75 mM (0.66 mg/ml) ascorbic acid towards the formation of MNU from the mixture of 7.5 mM MU + 7.5 mM NaNO2.     

Ecological aspects of thermoregulation at high altitudes: the case of andean Liolaemus lizards in northern Chile

Summary We document activity field temperatures, daily activity patterns, and extent of thermoregulation in four species of Liolaemus lizards inhabiting at high altitude (above 3500 m) in the Andes of northern Chile. These four species have similar activity field temperature (Tb near 29°C) despite their being distributed at different altitudinal belts. However, conspicuous differences exist between higher-altitude (L. alticolor and L. jamesi) and lower-altitude (L. islugensis and L. ornatus) lizards regarding extent of thermoregulation and activity period. Some differences in morphology, behavior, and patterns of microhabitat occupancy are also apparent among these four species and are seemingly related to the thermal environment to which they are subjected. In comparison to eight low-altitude Liolaemus species in central Chile (Tb near 35°C) the four high-altitude species in northern Chile have lower activity field temperature. The latter is apparently due to the constraints imposed by the harsh Andean thermal environment, a hypothesis supported by the fact that high-altitude Liolaemus lizards under laboratory conditions demonstrate body temperatures that exceed by 5°C or more, those recorded in the field.     

Aging and cerebral aminopeptidase activity

A comparative study of brain aminopeptidase activity between 18 month old male rats and young adults of 3 months has been carried out utilizing the arylamides Leu-, Arg-, Lys-, Tyr- and Asp-beta-naphthylamide as substrates. Statistical analysis of results showed no significant differences either in areas studied or for enzymatic activities detected when both ages were compared. Two different patterns of regional distribution of enzymatic activity were observed: One came to be as a result of the use of Lys-, Arg-, Leu- or Tyr-beta-naphthylamide and the other as a result of the use of Asp-beta-naphthylamide.     

Sequential estimation of nuclear DNA and silver staining of nucleoli in plant cells

A method for sequential estimation of nuclear DNA and silver staining of nucleoli in plant cells is described. Feulgen staining is done first and nuclear DNA estimated by absorption cytophotometry. Following this, the slides are stained with AgNO3. The method has been used to study the process of nucleolar fusion in garlic (Allium sativum L.) meristem root tip cells. It was found that during interphase nucleoli rarely fused, thus most fusion must have occurred before the G1 phase of the cell cycle.     

Cytochemical localization of calcium in renal sac nephrocytes of Helix aspersa

In renal sac nephrocytes of Helix aspersa, intracellular calcium has been localized using the oxalate-pyroantimonate (OPA) and phosphate-pyroantimonate (PPA) methods. Pyroantimonate precipitates are preferentially localized in the excretory spherule and in vesicles located in the basal and lateral regions of the nephrocyte. Such vesicles appear to release their content into the excretory vacuole. Calcium may interact with diverse types of molecules present in the excretory vacuole, thus favouring stabilization and packaging of the excretory spherule.     

Germination of concentrated suspensions of spores from Aspergillus niger

Summary Germination of condiospores fromA.niger in very concentrated suspension was required to inoculate solid fermentation media, but a germination self-inhibitor was detected in spores. It was found that the inhibitory effect depended on the composition of the medium and was reduced when glucose was used as a carbon source. The effect of the self-inhibitor was eliminated by washing the spores and using glucose and a protein nitrogen source in the germination medium. By this method it was possible to increase about 100 times (10⁶ to 10⁸) spore concentration, keeping more than 90% germination.