The temperate-tropical gradient of planktonic Protozoa and Rotifera

Many flagellates, ciliates and rhizopods appear to be cosmopolitan, at least when considered at the morphospecies level. There are indications of tropical endemics among the ciliates and the rhizopods, but the percentage of endemics appears to be low. Among the rotifers there is a well marked latitudinal gradient, but the picture is complicated by the occurrence of warm water species during hot summers in temperate regions. A further complication has been introduced by the artificial development of heated water associated with power stations. The characteristic rotifer associations of the tropics are governed largely by temperature and salinity. A study of the altitudinal distribution of rotifers in Africa reveals an interplay between latitude and altitude in determining the similarities of the associations to those found in the temperate Old World.     

Reducing the concentration of selected marker improves efficiency of cotransfer of unselected DNA into SV40-transformed human fibroblasts.

A substantial increase in transfer of unselected DNA to two human SV40-transformed fibroblast cell lines was obtained by reducing the concentration of the cotransferred selected marker DNA. The average amount of unselected DNA transferred, even under favorable conditions, was still low compared to that reported for some rodent cell lines. Our results suggest that in human fibroblasts there is strong competition between exogenous DNA molecules for integration and maintenance, and that more unselected DNA is retained in the presence of only one copy of the selected marker.     

Binding of correolide to K(v)1 family potassium channels. Mapping the domains of high affinity interaction.

Correolide, a novel nortriterpene natural product, potently inhibits the voltage-gated potassium channel, K(v)1.3, and [(3)H]dihydrocorreolide (diTC) binds with high affinity (K(d) approximately 10 nM) to membranes from Chinese hamster ovary cells that express K(v)1.3 (Felix, J. P., Bugianesi, R. M., Schmalhofer, W. A., Borris, R., Goetz, M. A., Hensens, O. D., Bao, J.-M., Kayser, F. , Parsons, W. H., Rupprecht, K., Garcia, M. L., Kaczorowski, G. J., and Slaughter, R. S. (1999) Biochemistry 38, 4922-4930). Mutagenesis studies were used to localize the diTC binding site and to design a high affinity receptor in the diTC-insensitive channel, K(v)3.2. Transferring the pore from K(v)1.3 to K(v)3.2 produces a chimera that binds peptidyl inhibitors of K(v)1.3 with high affinity, but not diTC. Transfer of the S(5) region of K(v)1.3 to K(v)3.2 reconstitutes diTC binding at 4-fold lower affinity as compared with K(v)1.3, whereas transfer of the entire S(5)-S(6) domain results in a normal K(v)1.3 phenotype. Substitutions in S(5)-S(6) of K(v)1.3 with nonconserved residues from K(v)3.2 has identified two positions in S(5) and one in S(6) that cause significant alterations in diTC binding. High affinity diTC binding can be conferred to K(v)3.2 after substitution of these three residues with the corresponding amino acids found in K(v)1.3. These results suggest that lack of sensitivity of K(v)3.2 to diTC is a consequence of the presence of Phe(382) and Ile(387) in S(5), and Met(458) in S(6). Inspection of K(v)1.1-1.6 channels indicates that they all possess identical S(5) and S(6) domains. As expected, diTC binds with high affinity (K(d) values 7-21 nM) to each of these homotetrameric channels. However, the kinetics of binding are fastest with K(v)1.3 and K(v)1.4, suggesting that conformations associated with C-type inactivation will facilitate entry and exit of diTC at its binding site. Taken together, these findings identify K(v)1 channel regions necessary for high affinity diTC binding, as well as, reveal a channel conformation that markedly influences the rate of binding of this ligand.     

Assessing hydraulic redistribution with the compensated average gradient heat-pulse method on rain-fed olive trees

Aims

In this study on hydraulic redistribution (HR) in roots, we aimed to use the calibrated average-gradient (CAG) heat-pulse method, the novelty being the use of a much narrower averaging window for the signal analysis, in order to achieve a more linear calibration curve, allowing the HR quantification.

Methods

The study was conducted in 12 large roots of a rain-fed olive orchard, for 6 months without significant rain, when the predawn leaf water potential decreased to ?2.4 MPa, and immediately following the first autumn rains.

Results

Detailed numerical modelling of the CAG method allowed verification of the response of the measurement system to a range of drivers, improving the linear range of the calibration response function, which has remained stable over the observations period. On average, reverse flow was observed during 30% of the summer nights and, in a conservative estimate, it increased to about 5% of total daily root flow before first autumn rain.

Conclusions

Reverse flow accounted on average for 2.6% of the total daily root flow, enabling upper roots to stay active during the very dry late-summer period. In qualitative terms, our results confirm the CAG method as a reliable tool to identify reverse flow and quantify HR when it occurs.