Effects of concanavalin a on pattern formation inHydrodictyaceae

Summary The effect of concanavalin A upon colony formation inPediastrum boryanum andHydrodictyon reticulatum was tested. Cell aggregation and the development of the pattern specific cell shape are influenced in both species; moreover, inPediastrum the lectin causes preservation of the swarming vesicle which normally persists only a short time after the zoospores have settled. With addition of horseradish peroxidase or application of fluoresceinconjugated concanavalin A binding of the lectin to the cell surface can be demonstrated. The existence of discrete adhesive sites on the zoospore surface which might be responsible for cell-cell recognition is being discussed.     

Adenosine dimethylation of 16S ribosomal RNA: effect of the methylgroups on local conformational stability as deduced from electrophoretic mobility of RNA fragments in denaturing polyacrylamide gels.

The electrophoretic mobility of RNA fragments derived from the 3'-end of 16S rRNA on slabs of polyacrylamide gel in the presence of urea is strongly influenced by dimethylation of the N6-aminogroup of two adjacent adenosines. This is not due to the presence of the methylgroups per se, but must be ascribed to an effect of methylation on long range intramolecular interactions at these denaturing conditions. When it is assumed that the electrophoretic mobilities of the RNA fragments in the polyacrylamide matrix are determined by the conformational state(s) of the fragments, dimethylation of the adenosines leads in the smaller fragments to a less compact average conformation and in the larger fragments to a more compact average conformation. An effort is made to comprehend the effects of adenosine dimethylation in terms of secondary structure based on nucleotide sequence.     

Epidemics in competition

When two or more epidemic agents are simultaneously present in a population, they may interact to increase or decrease each other's effectiveness. One form of interaction is competition where each agent confers immunity to the others. Such competition occurs, for example, between different strains of myxomatosis in rabbit populations. We consider some consequences of introducing competition into mathematical epidemic models. Both deterministic and stochastic simple epidemic models are examined. In either case the conclusions are similar: the faster spreading epidemic has a considerable advantage.     

Plant Growth Analysis: a Program for the Fitting of Lengthy Series of Data by the Method of B-splines*

A method is presented for fitting curves to lengthy and/or complicatedseries of data on plant growth. A computer program which derivesthe usual plant growth analytical quantities, and their errors,from these fitted curves is also described and offered for circulation.The fitted curves are splined cubic polynomial exponentials.Examples of their application are given, employing both realand artificial data. In any set of data the number of splines,and the position of the knots joining them, may be determinedeither by objective statistical tests or by the experimenterhimself, who thus retains a considerable degree of control overthe process but can call on the assistance of the program ifrequired. The value of this method is considered in relationto other curve-fitting approaches to plant growth analysis andit is concluded that, provided sufficient primary data are available,the method is free from many of the problems which beset earlierwork in this field, and also provides new possibilities of itsown. growth curves, approximating functions, empirical models, regression analysis, growth analysis     

A posteriori time-varying filtering of averaged evoked potentials

The problem of estimating an unknown transient signal, given an ensemble of waveforms, in which this signal appears as a nonrandom component in the presence of additive noise is considered. This problem is solved by generalizing the method of a posteriori Wiener filtering. In the new method, the ensemble average is filtered by a time-varying system which is based on estimated time-varying power spectra of signal and noise. The nature of this system, and the computational procedures involved, are discussed in detail. A software package for time-varying filtering is briefly described. Application of the method is illustrated by a simulation example, which also provides a comparison to time-invariant a posteriori Wiener filtering.     

Prolactin levels and the LH-response to synthetic LH-RH in the lactating sow

To determine the role of prolactin in the suppression of ovarian activity during lactation in the sow experiments were performed to investigate a possible inhibitory action of prolactin at the pituitary level. Therefore the LH-response to an intravenous injection of 25 μg synthetic LH-RH was measured in the 1st, 2nd and 3rd week of lactation. The compound was injected under high and low concentrations of prolactin in the peripheral blood, the latter achieved by removal of the piglets 6 h before administration of LH-RH. The results showed no difference in the effect of LH-RH injected at high or low prolactin levels. However, although the mean prolactin concentrations in the 1st, 2nd and 3rd week of lactation were similar, the results clearly demonstrated an increase in LH-response as lactation proceeds.The low responsiveness of the pituitary shortly post partum was also observed when the preparturient rise of prolactin was suppressed by treatment with bromoergocryptine. Injections of LH-RH in the last week of gestation given before and after the physiological increase of PRL, which occurred about 48 h before delivery, all showed low LH-response.It is obvious from the presented data that the LH-response to an intravenous injection of 25 μg LH-RH is in no way correlated with the prolactin levels at the time of treatment.     

Glycogen metabolic enzymes in the skeletal muscles of the developing chick embryo

In the skeletal muscles of the chick embryo from the 10th till the 15th day of embryogenesis, phosphorylase (EC. 2.4.1.1) is represented by two isozymes one of which corresponds, by electrophoretic mobility, to the liver phosphorylase and another to phosphorylase of the skeletal muscles of the adult rat. From the 17th day of embryogenesis on only one isozyme of phosphorylase is found in the skeletal muscles which is identical with that of the skeletal muscles of the adult bird. The isozyme spectrum of phosphorylase of the whole 4 days old embryo contains, besides phosphorylase L, a special "embryonic" isozyme which differs from that of the skeletal muscles by immunochemical characteristics and electrophoretic mobility. From the 10th day of embryogenesis till hatching, the activity of phosphorylase of the skeletal muscles increases more than 50 times and that of glycogen synthetase (EC. 2.4.1.11) only 4 times.