Entamoeba histolytica: Collagenolytic Activity and Virulence1

Several axenic strains of pathogenic and nonpathogenic Entamoeba histolytica were tested for their capacity to digest native radioactive type I collagen gels and to produce liver abscesses when injected into the liver of newborn hamsters. The results demonstrate that the pathogenic strains of amebas (HM1:IMSS, HM3:IMSS, HM38:IMSS, and HK9) have a collagenolytic activity that closely correlates with their in vivo capacity to produce liver lesions. The nonpathogenic isolate (Laredo) did not show collagenolytic activity and failed to produce lesions in the liver of newborn hamsters. The results also demonstrate that type I collagen obtained from rodents and cats is degraded less by amebic collagenase than is bovine collagen, which is similar to human collagen. These findings suggest that species susceptibility to invasive infection may depend, among other factors, on the characteristics of the extracellular components of host tissues.     

Importance of Time Constants in an Open Flow System: Mathematical Correction of Fast Ethylene Kinetics in Physiological Studies

A mathematical analysis for fast changes of ethylene concentration in an open flow system (non-steady-state conditions) is presented and experimentally tested. In this way it becomes possible to determine true values of ethylene production in the minute range following physiological and environmental changes which influence ethylene evolution. By this procedure ethylene kinetics can also be compared in absolute values independent of flow rate and plant chamber volume.     

Thermal Sensitivity as a Specialization for Prey Capture and Feeding in Snakes

Behavior can be regarded as a result of various processes ofdecision based on the information provided by the sensory organs.In this review the role of the so-called additional heat sense,next to vision, smell and mechanoreception is discussed withrespect to the feeding behavior of snakes. The hierarchy ofthe sensory information in various phases of the feeding behaviordiffers between snakes possessing heat receptors (e.g., speciesof the Crotalinae and Pythoninae) and those without (e.g., speciesof the Viperinae and Colubrinae). Probably depending on theinfluence of ecological demands, visual or chemical cues arethe main information in the behavioral phases before the strikeHowever, in situations with little visual input, e.g., in darkness,rodents' burrows, etc., hunting behavior is guided in the firstplace by radiation of warm objects in Crotalus, Python and Trimeresurusflavoviridis, and by substrate vibrations in Vipera aspis, Pituophismelanoleucus and Boa constrictor. I suggest that in the sensoryhierarchy, heat information functionally replaces the mechanicalinformation which is utilized by snakes without pit organs.Poststrike behavior on the other hand is mainly guided by chemicalcues in all snakes.     

Characteristics of the Wave of Depolarization Induced by Wounding in Bidens pilosa L.

Heating locally the hypocotyl of Bidens pilosa L. elicits awave of depolarization. The mechanism of the wave has been investigatedby means of microelectrophysiological techniques. The amplitudeof the transmembrane potential variation induced by an extracellularion concentration change (K⁺, Na⁺, Ca²⁺, Cl^–) was thesame in the resting conditions as during the slow wave. At pH4.0, the amplitude of the slow wave was reduced by 56% comparedwith the control performed at pH 7.0. In the presence of theuncoupler CCCP, the slow wave was not observed. The Ca²⁺ -chelatorEGTA and the Ca2²⁺ -channel blocker La³⁺ reduced, respectively,the amplitude of the slow wave by 78% and 68%. These resultsindicate the involvement of Ca²⁺ in triggering the slow wave.A transient modification of the electrogenic H⁺ pump activity(inactivation-activation) and of the transmembrane H⁺ flux inthe slow wave are discussed. Key words: Slow wave (of depolarization), wounding, electrogenic pump, calcium, Bidens pilosa L     

Production of ethylene by gravistimulation: a potential problem with the interpretation of data from some experimental techniques

Abstract. Gravistimulation was investigated as a potential and unwanted component in the interpretation of physiological investigations on plants. Using both seedlings and mature sunflower plants, two situations are described where gravistimulation contributes significantly to the outcome of an experiment not initially designed to include this parameter. The number of adventitious roots formed in derooted seedings decreased when the tops of the plants were allowed to bend over under their own weight, and the effect correlated positively with the rate of ethylene production by non-vertical stems. In droughted mature plants, and increase in leaf and stem ethylene caused by water stress was supplemented by additional ethylene produced in the lower halves of stems. Drought had caused these stem tissues to wilt, become gravistimulated, and thus produce more ethylene. Other situations in which gravistimulated ethylene production and its physiological consequences are likely to be complicating factors in experiments are discussed. It is concluded that procedures that unnecessarily place experimental material in non-vertical orientations should be avoided.     

An ethological framework for animal bioerosion trace fossils upon mineral substrates with proposal of a new class, fixichnia

Animal bioerosion trace fossils upon mineral substrates are analyzed from the point of view of the Seilacherian ethological classification. Several of the currently accepted ethological classes: cubichnia, fugichnia, repichnia, fodinichnia, agrichnia, calichnia and aedificichnia are not represented in these substrates. This fact points out a lower behavioral diversity of hard substrate trace fossils when compared with soft sediment trace fossils. Bioerosion traces can be classified in just five classes: domichnia, pascichnia, equilibrichnia, praedichnia and fixichnia. Fixichnia is here erected to gather superficial etching scars resulting from the anchoring of fixation of sessile epiliths by means of a soft or skeletal body part. Praedichnia and fixichnia are exclusive of the bioerosion realm.     

Two closely linked tomato HKT coding genes are positional candidates for the major tomato QTL involved in Na+/K+ homeostasis

The location of major quantitative trait loci (QTL) contributing to stem and leaf [Na⁺] and [K⁺] was previously reported in chromosome 7 using two connected populations of recombinant inbred lines (RILs) of tomato. HKT1;1 and HKT1;2, two tomato Na⁺‐selective class I‐HKT transporters, were found to be closely linked, where the maximum logarithm of odds (LOD) score for these QTLs located. When a chromosome 7 linkage map based on 278 single‐nucleotide polymorphisms (SNPs) was used, the maximum LOD score position was only 35 kb from HKT1;1 and HKT1;2. Their expression patterns and phenotypic effects were further investigated in two near‐isogenic lines (NILs): 157‐14 (double homozygote for the cheesmaniae alleles) and 157‐17 (double homozygote for the lycopersicum alleles). The expression pattern for the HKT1;1 and HKT1;2 alleles was complex, possibly because of differences in their promoter sequences. High salinity had very little effect on root dry and fresh weight and consequently on the plant dry weight of NIL 157‐14 in comparison with 157‐17. A significant difference between NILs was also found for [K⁺] and the [Na⁺]/[K⁺] ratio in leaf and stem but not for [Na⁺] arising a disagreement with the corresponding RIL population. Their association with leaf [Na⁺] and salt tolerance in tomato is also discussed.