Changes in the water status and rheological characteristics of pea seedling axillary buds during their transitions growth-dormancy-growth in apical dominance

The technique of isopiestic thermocouple psychrometry was used for the analysis of bud transition from dormancy to growth and back in 8-18-day-old pea (Pisum sativum L.) seedlings. We monitored changes in the water (ψ_w) and osmotic (ψ_{s + m}) potentials and also turgor pressure (ψ_p) in dormant buds and threshold turgor (Y) in growing buds, the latter being one of the cell-wall rheological characteristics. Seedling decapitation resulted in a decrease of Y in the bud, which coincided with the start of its outgrowth. The replacement of terminal shoot with exogenous auxin (IAA or NAA) retarded bud outgrowth and maintained the high level of Y, which argues for the auxin control of this parameter. When growth of the first axillary bud was inhibited by the second one, positioned higher and remained on the plant, the beginning of Y increase preceded visible correlative growth suppression; this makes this rheological index an early marker of bud transition from growth to dormancy. The effects of the terminal shoot part and auxin application on the bud osmotic status differed substantially. In fact, bud transition to dormancy in the presence of the terminal shoot, the main or developing from the second axillary bud, was accompanied by the rise in ψ_{s + m}, whereas, in the case of the replacement of the second bud with exogenous auxin, the first bud growth suppression occurred with the decrease in ψ_{s + m}. The low value of the bud ψ_{s + m} is a factor for creating a considerable gradient of the water potential between the stem and bud supporting water transport to the bud, which was much more active than in plants with a terminal shoot. It seems likely that this is the reason for the absence of complete growth suppression observed by us and other researchers even after application of high auxin concentrations. Immediately after seedling decapitation, ψ_{s + m} in the buds reduced; however, this was not the result of trophic metabolite redistribution due to the loss of their active sink because ψ_{s + m} reduced also in experiments with complete isolation of the bud releasing from dormancy in the chamber at 100% humidity. Auxin application to the cut surface of decapitated seedlings did not affect the ψ_{s + m} decrease. Like decapitation, cotyledon removal resulted in the increase in the bud turgor pressure. However, in this case, water stress did not change the bud osmotic status. Thus, the induction of osmotica accumulation in the bud after the removal of the terminal shoot is evidently related to neither trophic, nor auxin, nor hydraulic signal. The data obtained allowed us to conclude that both components of the bud water potential—ψ_{s + m} and Y—play an important role in the control of bud growth at apical dominance. Auxin produced in the shoot apex is involved in the control of Y, whereas the nature of the signal controlling the ψ_{s + m} level is unclear.     

A systems model for immune cell interactions unravels the mechanism of inflammation in human skin

Inflammation is characterized by altered cytokine levels produced by cell populations in a highly interdependent manner. To elucidate the mechanism of an inflammatory reaction, we have developed a mathematical model for immune cell interactions via the specific, dose-dependent cytokine production rates of cell populations. The model describes the criteria required for normal and pathological immune system responses and suggests that alterations in the cytokine production rates can lead to various stable levels which manifest themselves in different disease phenotypes. The model predicts that pairs of interacting immune cell populations can maintain homeostatic and elevated extracellular cytokine concentration levels, enabling them to operate as an immune system switch. The concept described here is developed in the context of psoriasis, an immune-mediated disease, but it can also offer mechanistic insights into other inflammatory pathologies as it explains how interactions between immune cell populations can lead to disease phenotypes.     

A calcium dependent de-adhesion mechanism regulates the direction and rate of cell migration: a mathematical model

Cell migration has long been studied by a variety of techniques and many proteins have been implicated in its regulation. Integrins, key proteins that link the cell to the extracellular matrix, are central to adhesion complexes whose turnover defines the rate of cell locomotion. The formation and disassembly of these adhesions is regulated by both intracellular and extracellular factors. In this study we have focused on the Ca2+-dependent protein network (module) that disassembles the adhesion complexes. We have developed a mathematical model that includes the Ca2+-dependent enzymes micro-calpain and phospholipase C (PLC) as well as IP3 receptors and stretch activated Ca2+ channels, all of which have been reported to regulate migration. The model also considers the spatial effects of Ca2+ propagation into lamella. Our model predicts differential activation of calpain at the leading and trailing edges of the cell. Since disassembly of integrin adhesive contacts is proportional to the degree of calpain activation, this leads to cell migration in a preferred direction. We show how the dynamics of Ca2+ spiking affects calpain activation and thus changes the disassembly rate of adhesions. The spiking is controlled by PLC activity and currents through stretch-activated Ca2+ channels. Our model thus combines the effects of various molecular factors and leads to a consistent explanation of the regulation of the rate and direction of cell migration.     

Comparative analysis of motivation-activated effects of angiotensins in rats

The effects of angiotensin-II, angiotensin-III, and [des-Asp1-angiotensin-I on drinking and attendant behaviors of rats were studied. Special behavioral patterns were observed after intracerebroventricular administration of angiotensins. The nature and possible mechanisms of behavioral effects of peptidergic brain stimulation are discussed.     

Ecological remarks on Mastigodiaptomus nesus Bowman, 1986(Copepoda: Calanoida) in a Mexican karstic sinkhole

Mastigodiaptomus nesus(Bowman, 1986) was previously described from the West Indies, and its distribution was considered restricted to these islands. Recently it has been detected in several systems from the continental Yucatan Peninsula in Mexico. In this study, we contribute to the body size variability, abundance, distribution and vertical migration of Mastigodiaptomus nesus dwelling in a small, deep (264 m ², 47 m deep) karstic beaker-shaped sinkhole, located in this Peninsula. Here, this species is an important component of the zooplankton community during all the year. We analyzed the relationship between its abundance and concentration of nutrients (NO ⁻³), and Chlorophyll α. Differences in body size by sex (F = 67.56, p < 0.0001; n = 180), and sampled season (F = 6.59, p < 0.01; n = 180) were found. When animals from this sinkhole were compared with other localities, size difference was detected. Bigger animals were found in the West Indies, and smaller ones in continental localities. The nauplii were the most abundant development instars, followed by copepodids, and adults. In general, all developmental instars had a normal migration, with higher abundance at night time in upper layers (0.5 and 5 m), and diminishing towards daylight time. Direction of migrations seems to be towards the walls of the sinkhole (horizontal migration) instead of the deeper water layers, suggesting that these copepods are hidden in the irregular calcareous walls of the sinkhole. Abundance of total copepodid developmental stages were correlated with the Chl-α concentration. In addition, we found a highly significant difference between Chl-α concentration (F = 24.172, p < 0.001, n = 72), and NO ⁻³ concentration at all strata among seasons (F=25.46, p < 0.001, n = 60). Our results suggest that the body size of M. nesus is influenced by the nutrient concentration, and its vertical abundance and distribution may be explained by food availability.     

Effect of the body antiorthostatic posture on various circulation and respiration parameters in anesthetised cats

In anaesthetised cats, antiorthostatic posture of the body with an inclination angle of 30 degrees increased pressure in the vena cava superior and in jugular vein. The rest of the cardio-respiratory parameters were changed insignificantly. Physical and physiological mechanisms of the blood regional redistribution in alteration of the body gravitation orientation, are discussed.     

Analysis of the Ilyocryptus spinifer-species group (Anomopoda,Branchiopoda), with description of a new species

We studied the morphology and variability of Ilyocryptus spinifer Herrick, 1882 from different parts of the world using optical microscopy and SEM, re-examining type material wherever possible. Morphometric analysis failed to reveal significant regional differences between populations. The following species names for members of Ilyocryptus spinifer group, I. halyi Brady, 1886; I. longiremis Sars, 1888; I. immundus F. Mueller in Ihering, 1895; I. verrucosus Daday, 1905; and I. tetraspinatus Berganim, 1939, are junior synonyms of I. spinifer. A new species from this group is described from Queensland, Australia. Ilyocryptus timmsi n. sp. shows unique morphological characters in the armature of the lateral swimming setae of the antennal endopod, its apical segment and the postabdominal claws.     

Redescription of Ilyocryptus tuberculatus Brehm, 1913 (Anomopoda,Branchiopoda)

The morphology of Ilyocryptus tuberculatus Brehm, 1913 is redescribed, based on material from the Niger basin, Africa. The species name was given by Brehm erroneously, because under an optical microscope he mistook internal structures (the columns between the outer and inner walls of the valves) for the tubercules on the valve surface. But this species is undoubtedly valid, and `incorrect' species names must be conserved. Differences between I. tuberculatus and the most similar I. agilis (probably absent from the majority of African waters), I. spinifer (common in Africa), and some other species are discussed. Currently, I. tuberculatus is known for the Central African Republic, Mali and Niger.     

Characteristics of physiological reactions during long-term immunization of rats with protein conjugates of angiotensin II

The results show that during long-term immunization of rats against conjugates of angiotensin II with bovine serum albumin definite age dynamics of immune response have been observed. It was shown that the changes of physiological readings were correlated with growing of antibodies titer against angiotensin II, accordingly, as the immune response was lower, these readings return to the initial level.