Circadian communication between unicells?

Populations ofGonyaulax polyedra, in two different phases, about 11 h apart, were mixed, and the intensity of their spontaneous bioluminescence glow recorded for about 2 wk under conditions of constant dim (35±3 μE/m²/s) white light and constant temperature (19.0±0.3°C). The phases and amplitudes of glow signals recorded from mixed cultures were compared with those obtained from the arithmetic sum of the intensity data from two control vials. Peaks in control cultures generally remained separate, but there was a spontaneous increase in the period beginning 6–11 d after the onset of constant conditions. This did not occur in cultures in which the medium was exchanged with fresh medium every 2 d. In the actual mixes of two cultures there was a merging of the two subpeaks in the signal, which did not occur when the medium was exchanged. The results indicate that conditioning of the medium by cells may affect the period of the circadian rhythm and that this might result in a type of communication. Supported by the Deutsche Forschungsgemeinschaft; present address     

Estimation of the Temporal Course of Evoked Secretion of Transmitter Quanta in the Frog Neuromuscular Junction

In experiments on the cutaneothoracic muscle of the frog, we recorded, using the technique of two-electrode voltage clamp at a normal Ca²⁺ concentration (1.8 mM), multiquantum end-plate currents (EPC) and miniature uniquantum EPC (mEPC). Multiquantum signals, when compared with uniquantum currents, were characterized by longer leading and trailing edges. The quantum composition of multiquantum signals estimated according to the ratios of EPC and mEPC amplitudes was, on average, 27% lower than that calculated according to the ratios of their integral values (areas). These data demonstrate that stimulus-evoked transmitter secretion from the motor nerve endings is noticeably asynchronous. Based on the parameters of the experimental EPC and mEPC, we estimated the temporal course of evoked secretion using various techniques: spectral analysis, a system of linear equations, and Van der Kloot's method. Using convolution with uniquantum signals, we found that spectral analysis is the best technique for such estimation. Calculated parameters of the temporal course of secretion were the following: risetime 0.20 msec and decay time constant 0.33 msec. The respective distribution significantly differed from that of the synaptic delays of extracellularly recorded uniquantum EPC by longer durations (150-200%) of the leading and trailing edges. We hypothesize that these differences are related to the geometry of the junction and the temporal sequence of switching on of the active zones in the nerve ending upon their activation by spreading action potentials. Factors influencing the temporal course of evoked secretion of the transmitter in the junction under study (its asynchronicity, in particular) are discussed.     

Prediction of the performance of inbred lines derived from a population cross in autumn-sown onions (Allium cepa L.)

Summary A design and model are presented to allow the prediction, in early generations, of the mean and distribution of recombinant inbred lines derived from a cross between two parental populations or partially inbred lines. The procedure has been tested in autumn-sown onions (in the UK) using a wide cross between the openpollinated Japanese cultivar, Senshyu, and a partially inbred line derived from the European cultivar, Rawska. The early generations used for prediction included the first self-pollinated generation of the two parental populations and the F₃ generation produced from the hybrid population. The predictions were tested by reference to the field performance of a random array of inbred lines, which were produced by single-seed descent (SSD) and had been selfed for three generations. The early generations, used for prediction, and a sample of SSD lines were raised alongside each other in each of two seasons. Within each season, good agreement was found between the predicted and observed performance of the recombinant inbred lines for three characters — yield, quality and maturity. This is used as evidence of the validity of the genetical model and the assumptions made. The effects of genotype x environment interactions prevented predictions made in one season being reliably applied to those made in the other and, therefore, reduce the attraction of this type of prediction study to the plant breeder.     

Solvent effects on the structure,dynamics and activity of lysozyme

Kuntz and Kauzmann have argued that dehydrating a protein results in conformational changes. In contrast, Rupleyet al. have developed a hydration model which involves no significant change in conformation; the onset of enzyme activity in hen egg-white lysozyme at hydration values of about 0.2 g water/g protein they ascribe rather to a solvation effect. Using a direct difference infra-red technique we can follow specific hydration events as water is added to a dry protein. Conformational studies of lysozyme using laser Raman spectroscopy indicate changes in conformation with hydration that are complete just before measurable activity is found. Parallel nuclear magnetic resonance measurements of exchangeability of the main chain amide hydrogens, as a function of hydration from near dryness, suggest a hydration-related increase in conformational flexibility which occurs before-and is probably necessary for-the Raman-detected conformational changes. Very recent inelastic neutron scattering measurements provides direct evidence of a flexibility change induced by hydration, which is apparently necessary before the enzyme can achieve adequate flexibility for it to begin to function.