Electrical aspects of division control inSaccharomyces

Readily discernable changes in electrical character take place during the division cycle of the yeast,Saccharomyces cerevisiae. By using the technique of cellular spin resonance, the electrical polarizability of individual cells can be seen to change with the life cycle, as determined by cell morphology. The polarizability changes indicate that during the advance through the life cycle, the ionic double layers associated with the outer cell wall gradually tighten.     

Constant rate allocation in nymphal development in species of Hemiptera

Abstract. This study investigated the existence of rate isomorphy (the constant allocation of relative times to different stages of development under different abiotic conditions) in Macrolophus pygmaeus (Hemiptera: Miridae; a phytophagous and predatory insect). Replicated data were used from a range of temperatures regarding (i) the developmental period of each nymphal stage in relation to the total duration of nymph development, when feeding on three host plants either with different prey species or without prey, and (ii) its egg, total nymphal and preoviposition period, on two host plants, with different prey species. The proportion of time required for the development of each nymphal stage of M. pygmaeus is not different among the temperatures or the kind of food available. These proportions ranged among the different host plants, temperatures and prey presence/absence from 17.3–21.8% in the first, 14.5–18.8% in the second, 14.2–18.3% in the third, 16.5–21.0% in the fourth and from 25.4–30.6% in the fifth nymphal stage. Thus, temperature does not significantly affect the proportion of time spent in each nymphal stage and rate isomorphy exists in nymphal development. This phenomenon was also investigated using data from the literature, and it also occurs in several other Hemiptera species. Therefore, there appears to be a constant time allocation in the nymphal development of the higher taxonomic groups of insects. However, for M. pygmaeus, rate isomorphy does not hold when considering egg‐to‐egg development and the relative duration of times to egg hatch, total nymphal development and preoviposition period. The ecophysiological implications of this rate isomorphy phenomenon are discussed in relation to endocrinological mechanisms. Apart from its theoretical interest, the existence of rate isomorphy simplifies studies on the rate of development and the estimation of thermal constants of an insect, which are essential for the prediction of insect population dynamics. It is also proposed that the term ‘rate isomorphy’ does not strictly describe the phenomenon, and it is suggested that ‘constant rate allocation’ would be a more suitable term.     

Quasi one-dimensional electronic conduction and nomadic polarization in polymers

The molecular semiconductors exhibit a wide range of electronic properties not necessarily shown by conventional covalent or ionic semiconductors. Study of the conductive organic solids, particularly the polymeric as opposed to the charge-transfer type, is fruitful because of the deeper insights they offer as to carrier birth and transport in systems possessing short range order. Conduction in the polymeric organic solids is of the hopping type, increasing with frequency of the applied field. As judged from the thermoelectric power, it may be dominated by either holes or electrons, depending upon the chemical makeup. It is not certain from Hall effects studies whether the Hall ‘mobilities’ are normal or suppressed, such as found in amorphous covalent solids. Both the intra- and inter-chain mobilities are frequency dependent. Polarization in the polymeric organic solids is observed on occasions to become very large. This is due to a unique form of polarizability,nomadic polarization, wherein certain charges are free to roam over large ranges before being blocked. The large dielectric constants observed are temperature, pressure, and frequency dependent.     

Bahiaxenidae, a "living fossil" and a new family of Strepsiptera (Hexapoda) discovered in Brazil

An adult male of a newly discovered strepsipteran species from Brazil— Bahiaxenos relictus— is described. A new family Bahiaxenidae is suggested based on cladistic analyses of comprehensive morphological data sets with a broad taxon sampling including the stem group. It is unambiguously placed as the sister group of all other extant families of Strepsiptera. Bahiaxenos relictus is the only species of basal, i.e. non-stylopidian, Strepsiptera occurring in the New World. It appears to be a relict taxon that has survived in the fossil sand dunes of the São Francisco River (Bahia State). The loss of the 8th antennomere and the greatly reduced labrum are autapomorphies of Strepsiptera s.s . excluding Bahiaxenidae. The sister group relationship between†Protoxenidae and the remaining Strepsiptera, and between † Cretostylops and a clade comprising † Mengea and Strepsiptera s.s. , is confirmed, as is the monophyly of Stylopidia and Stylopiformia.     

Dynamic dielectrophoretic levitation of living individual cells

The levitation of lone live cells by means of dielectrophoretic force provides a means of determining the relative polarization of the cells and their aqueous support medium. When done over a range of frequencies, a spectrum of dielectric (polarization) responses is obtained which serves to characterize a single living ell. In this manner, individual cells of several microorganisms,Saccharomyces cerevisiae andNetrium digitus, were investigated in the frequency range 10² to 10⁶ Hz. These and related prior studies showed that the positive dielectrophoresis, i.e. where the suspended particle has a greater net polarization than the suspending medium, can be — used to show subtle differences between species, and even between cells of the same culture when using this technique.     

Rapid transmembrane diffusion of ceramide and dihydroceramide spin-labelled analogues in the liquid ordered phase

In order to study the basic physical phenomena underlying complex lipid transbilayer movement in biological membranes, we have measured the transmembrane diffusion of spin-labelled analogues of sphingolipids in phosphatidylcholine (PC) large unilamellar vesicles in the absence or presence of cholesterol, going from a fluid ( liquid disordered) l_d, phase to a more viscous, liquid ordered (l_o), phase. We have found cholesterol to reduce the transverse diffusion of glucosylceramide (GlcCer) and galactosylceramide (GalCer) in a concentration-dependent manner. However, surprisingly, we could neither detect any influence of cholesterol on the rapid flip-flop of ceramide nor on the flip-flop of dihydroceramide, for which the τ_1/2 of flip-flop remains in the order of 1 minute at 20°C in the presence of cholesterol. As a consequence of rapid flip-flop of ceramide in both the l_o and the l_d phase, ceramide is likely to distribute between the two monolayers of a membrane, and could in principle partition into segregated domains in each side of the plasma membrane of eukaryotic cells.     

DNA sequencing with direct blotting electrophoresis.

A method for transferring the DNA molecules of sequencing reaction mixtures onto an immobilizing matrix during electrophoresis has been developed. A blotting membrane moves with constant speed across the end of a very short, denaturing gel and collects the molecules according to size. A constant distance between bands for molecules differing in length by one nucleotide is obtained over a large range (approximately 600 nucleotides with a 5% gel), simplifying the determination of DNA sequences considerably. Reliable sequences of 500 nucleotides can be read and sequence features up to greater than 1000 nucleotides are revealed in a single experiment. The sequencing of a potential Z-DNA-forming fragment from Escherichia coli DNA is given as an example and possible further developments are discussed.