Oscillations of membrane potential during inhibition of cytoplasmic streaming in Characean internodes

Oscillatory changes in electrical parameters of cells of Nitellopsis obtusa (Desv. in Lois) J. Gr. and Nitella flexilis f. Atkahensis R. D. W., particularly in the membrane potential, were investigated with external Ag/AgCl electrodes. Three main types of oscillations were observed. The measurements were carried out on 30 cells with the application of an inhibitor of cytoplasmic streaming (procaine) and revealed that there was no direct correlation between cytoplasmic streaming and oscillations in the membrane potential.     

Daily Variations in the Sensitivity of Soybean Seedlings to Low Temperature

Every 4 hr during a time span of 32 hr and of 76 hr a different group of soybean seedlings [Glycine max (L.) Merr., cv. Corsoy] maintained under a regime of 16 hr of light followed by 8 hr of darkness was exposed to -10°C for 4 min. Extent of sensitivity to low temperature was evaluated approximately 10 days alter exposure to freezing temperature by determining the weight of the plants and chlorophyll content of the cotyledons. The amount of sensitivity to low temperature was related to the time of exposure and displayed a significant 24-hr oscillation. Plants appeared to be least sensitive to cold injury during the late portions of the light span. Plants subjected to water stress were less sensitive to cold and no significant 24-hr oscillation in response to low temperature could be detected by the cosinor method of analysis.     

Self‐organized partitioning of dynamically localized proteins in bacterial cell division

How cells manage to get equal distribution of their structures and molecules at cell division is a crucial issue in biology. In principle, a feedback mechanism could always ensure equality by measuring and correcting the distribution in the progeny. However, an elegant alternative could be a mechanism relying on self‐organization, with the interplay between system properties and cell geometry leading to the emergence of equal partitioning. The problem is exemplified by the bacterial Min system that defines the division site by oscillating from pole to pole. Unequal partitioning of Min proteins at division could negatively impact system performance and cell growth because of loss of Min oscillations and imprecise mid‐cell determination. In this study, we combine live cell and computational analyses to show that known properties of the Min system together with the gradual reduction of protein exchange through the constricting septum are sufficient to explain the observed highly precise spontaneous protein partitioning. Our findings reveal a novel and effective mechanism of protein partitioning in dividing cells and emphasize the importance of self‐organization in basic cellular processes.     

The Middle‐Upper Tournaisian boundary event

The Middle‐Upper Tournaisian boundary broadly correlating with the Kinderhookian‐Osagean boundary in North America represents a level of a conspicuous lithological as well as biotic change. The decline of Chernyshinella and increased representation of eurythermal and agglutinated forms marks the end of Cherepet evolutionary cycle in calcareous foraminifers. In conodonts the decline of Siphonodella inhabiting the pelagic to hemipelagic dysphotic to aphotic environment accompanied by a widespread dispersal and diversification of nektobenthic gnathodids characterizes the end of the first Tournaisian conodont cycle. A major regression associated with important sedimentological changes marks the boundary between the middle and upper Tournaisian mega‐sequences. The above changes in fauna and lithology seem to be connected with climatic oscillations and accompanying oceanographic changes. They are a part of the broader Upper Devonian‐Lower Carboniferous cyclic scheme which appears to have been modified by a complicated interplay of cyclic and nonrecurring processes.     

Circadian Locomotor Activity Rhythm in the Freshwater Crab Pseudothelphusa americana (De Saussure, 1857): Effect of Eyestalk Ablation

The circadian rhythm of locomotor activity in the freshwater crab, Pseudothelphusa americana, was studied in aquaria using infrared crossing sensors. Individuals with ablated eyestalks were compared with intact individuals in constant darkness (DD) and in light-dark cycles (LD). Our results showed that intact animals in DD displayed bimodal rhythms. In LD conditions the two peaks were associated with lights on and lights off, respectively. A significant difference in the free running periods before and after LD was observed in all intact animals. After eyestalk ablation (ES-X), the circadian rhythm of locomotor activity disappeared immediately, but reappeared several days later. Diurnal activity was seen in some ES-X animals when exposed to LD. Our results indicate that locomotor activity rhythm in P. americana is driven primarily by oscillators located outside the eyestalks, and that extraretinal photoreceptors mediate either entrainment or masking effects.