Testosterone and year‐round territoriality in tropical and non‐tropical songbirds

Past studies have suggested a fundamental difference in testosterone concentrations between tropical and northern latitude male birds, with the convention being that males in the tropics express much lower levels of testosterone. However, recent comparative studies have shown that tropical males with a short and synchronous breeding season (i.e. a breeding season typical of northern species) express maximum testosterone levels similar to those of northern latitude birds. Here, we ask the converse: do northern latitude songbirds that express a defining life‐history characteristic typical of the tropics, i.e. year‐round territoriality, have an annual testosterone profile similar to that of tropical songbirds? For the few year‐round territorial species for which data are available, we found that seasonal testosterone profiles and seasonal maxima in plasma testosterone were similar between males of tropical and non‐tropical species. For example, males of both groups expressed seasonal maxima during the period when females were fertile, and testosterone levels at this time were similar. In contrast, this and other studies show that species with seasonal territories typically express maximum testosterone levels earlier in the breeding cycle, when territories are first being established. Taken together, we suggest that specific life‐history traits may play a more important role in determining testosterone profiles of tropical and non‐tropical birds than breeding latitude and encourage further studies to allow for more formal comparisons.     

Size of the pores created by an electric pulse: Microsecond vs millisecond pulses

Here, the sizes of the pores created by square-wave electric pulses with the duration of 100μs and 2ms are compared for pulses with the amplitudes close to the threshold of electroporation. Experiments were carried out with three types of cells: mouse hepatoma MH-22A cells, Chinese hamster ovary (CHO) cells, and human erythrocytes. In the case of a short pulse (square-wave with the duration of 100μs or exponential with the time constant of 22μs), in the large portion (30-60%) of electroporated (permeable to potassium ions) cells, an electric pulse created only the pores, which were smaller than the molecule of bleomycin (molecular mass of 1450Da, r≈0.8nm) or sucrose (molecular mass of 342.3Da, radius-0.44-0.52nm). In the case of a long 2-ms duration pulse, in almost all cells, which were electroporated, there were the pores larger than the molecules of bleomycin and/or sucrose. Kinetics of pore resealing depended on the pulse duration and was faster after the shorter pulse. After a short 100-μs duration pulse, the disappearance of the pores permeable to bleomycin was completed after 6-7min at 24-26°C, while after a long 2-ms duration pulse, this process was slower and lasted 15-20min. Thus, it can be concluded that a short 100-μs duration pulse created smaller pores than the longer 2-ms duration pulse. This could be attributed to the time inadequacy for pores to grow and expand during the pulse, in the case of short pulses.     

Oxidative effects of nanosecond pulsed electric field exposure in cells and cell-free media

Nanosecond pulsed electric field (nsPEF) is a novel modality for permeabilization of membranous structures and intracellular delivery of xenobiotics. We hypothesized that oxidative effects of nsPEF could be a separate primary mechanism responsible for bioeffects. ROS production in cultured cells and media exposed to 300-ns PEF (1-13kV/cm) was assessed by oxidation of 2',7'-dichlorodihydrofluoresein (H(2)DCF), dihidroethidium (DHE), or Amplex Red. When a suspension of H(2)DCF-loaded cells was subjected to nsPEF, the yield of fluorescent 2',7'-dichlorofluorescein (DCF) increased proportionally to the pulse number and cell density. DCF emission increased with time after exposure in nsPEF-sensitive Jurkat cells, but remained stable in nsPEF-resistant U937 cells. In cell-free media, nsPEF facilitated the conversion of H(2)DCF into DCF. This effect was not related to heating and was reduced by catalase, but not by mannitol or superoxide dismutase. Formation of H(2)O(2) in nsPEF-treated media was confirmed by increased oxidation of Amplex Red. ROS increase within individual cells exposed to nsPEF was visualized by oxidation of DHE. We conclude that nsPEF can generate both extracellular (electrochemical) and intracellular ROS, including H(2)O(2) and possibly other species. Therefore, bioeffects of nsPEF are not limited to electropermeabilization; concurrent ROS formation may lead to cell stimulation and/or oxidative cell damage.     

Floral meristems as a source of enhanced yield and quality of DNA in grasses

Floral meristems of Lolium and Festuca grasses give a 5- to 19-fold enhancement in yield of extracted DNA in comparison with leaves. Meristems also provide highly pure DNA samples. The method could be useful for applications in molecular genetics in many species of the Gramineae. Received: 14 April 1998 / Revision received: 8 June 1998 / Accepted: 10 July 1998     

The roles of carbonic anhydrases IX and XII in cancer cell adhesion,migration, invasion and metastasis

The main function of carbonic anhydrases (CAs) in cancer cells is the pH regulation through a conversion of H₂O and CO₂ to H⁺ and HCO₃⁻. However, the data of in vitro and in vivo studies have demonstrated that transmembrane isoforms of CA IX and CA XII are involved in various steps of cancer cell migration, invasion and metastasis. According to literature, inhibition of these CAs can affect the expression of multiple proteins. Some scientific groups have reported the possible interactions between CA IX and E-cadherin–catenin system, CA IX and integrins, CA IX, CA XII and ion transporters, which all are highly involved in cell-to-cell adhesion, the formation of membrane protrusions and focal adhesions. Nevertheless, CA IX and CA XII have a high impact on tumour growth and metastases formation. The data discussed in this review are quite recent. It highly support the role of CA IX and CA XII in various cancer metastasis processes through their interactions to other invasion proteins. Nevertheless, all findings show the great potential of these CAs in the context of research and application in clinical use.     

The impacts of heavy metals on oxidative stress and growth of spring barley

Oxidative stress is accepted to play a significant role in stress symptoms, caused by different stressors in a variety of organisms. In this study seedlings of spring barley (Hordeum vulgare L.) were exposed to a wide range of copper, zinc, chromium, nickel, lead and cadmium concentrations in order to determine the relationships between heavy metals-induced oxidative stress and plant growth inhibition. All investigated heavy metals induced an essential increase in lipid peroxidation and a reduction of dry biomass along with an increase in metal concentration in the nutrient solution. A very close and statistically significant exponential relationship between lipid peroxidation and growth inhibition was detected in this study. According to the results of analysis of variance (ANOVA), the intensity of nonspecific oxidative stress is identified as the main factor of barley growth inhibition, explaining 75% of total variance. Almost 10% of growth inhibition is attributed to the specific impact of heavy metals. The most pronounced increase of malondialdehyde content and growth inhibition was observed in Cu and Cd treatments, whereas the lowest changes in observed indicators were detected after exposure to Zn and Pb.     

Current state of purification,isolation and analysis of bacteriocins produced by lactic acid bacteria

Applied Microbiology and Biotechnology - The scientific interest for the search of natural means of microbial inhibitors has not faded for several years. A search of natural antibiotics, so-called...     

Ragweed plants and airborne pollen in the Baltic states

Presence of pollen in the atmosphere was determined inTartu in 1989–1997, in Kuressaare in 1996–1997 and iniauliai in 1997. Ragweed airpollen was found in latesummer in three years. The distribution, abundance andflowering of local ragweed plants were estimated. Itappeared that the number of local sources did notexceed twenty per country per year. Majority of thesesources consisted of a small number of pollinating A. artemisiifolia individuals. The largest localsources, consisting of several hundreds ofindividuals, were exclusively rare. Transport ofragweed pollen by air masses from distant sources wasstudied. It was found that incursions of ragweedpollen were determined by air fluxes originating fromthe Ukraine as well as from the southeastern andsouthern regions of the European part of Russia. Theseincursions occurred in extensive high-pressure areaswhose centre was located in the central region of theEuropean part of Russia with a periphery extending tothe Baltic countries.