Changes in seasonal streamflow extremes experienced in rivers of Northwestern South America (Colombia)

A measure of the variability in seasonal extreme streamflow was estimated for the Colombian Caribbean coast, using monthly time series of freshwater discharge from ten watersheds. The aim was to detect modifications in the streamflow monthly distribution, seasonal trends, variance and extreme monthly values. A 20-year length time moving window, with 1-year successive shiftments, was applied to the monthly series to analyze the seasonal variability of streamflow. The seasonal-windowed data were statistically fitted through the Gamma distribution function. Scale and shape parameters were computed using the Maximum Likelihood Estimation (MLE) and the bootstrap method for 1000 resample. A trend analysis was performed for each windowed-serie, allowing to detect the window of maximum absolute values for trends. Significant temporal shifts in seasonal streamflow distribution and quantiles (QT), were obtained for different frequencies. Wet and dry extremes periods increased significantly in the last decades. Such increase did not occur simultaneously through the region. Some locations exhibited continuous increases only at minimum QT

Conformational dynamics are a key factor in signaling mediated by the receiver domain of a sensor histidine kinase from Arabidopsis thaliana

Multistep phosphorelay MSP cascades mediate responses to a wide spectrum of stimuli, including plant hormonal signaling, but several aspects of MSP await elucidation. Here, we provide first insight into the key step of MSP mediated phosphotransfer in a eukaryotic system, the phosphorylation of the receiver domain of the histidine kinase CYTOKININ INDEPENDENT 1 CKI1RD from Arabidopsis thaliana. We observed that the crystal structures of free, Mg2 bound, and beryllofluoridated CKI1RD a stable analogue of the labile phosphorylated form were identical and similar to the active state of receiver domains of bacterial response regulators. However, the three CKI1RD variants exhibited different conformational dynamics in solution. NMR studies revealed that Mg2 binding and beryllofluoridation alter the conformational equilibrium of the amp; 946;3 amp; 945;3 loop close to the phosphorylation site. Mutations that perturbed the conformational behavior of the amp; 946;3 amp; 945;3 loop while keeping the active site aspartate intact resulted in suppression of CKI1 function. Mechanistically, homology modeling indicated that the amp; 946;3 amp; 945;3 loop directly interacts with the ATP binding site of the CKI1 histidine kinase domain. The functional relevance of the conformational dynamics observed in the amp; 946;3 amp; 945;3 loop of CKI1RD was supported by a comparison with another A. thaliana histidine kinase, ETR1. In contrast to the highly dynamic amp; 946;3 amp; 945;3 loop of CKI1RD, the corresponding loop of the ETR1 receiver domain ETR1RD exhibited little conformational exchange and adopted a different orientation in crystals. Biochemical data indicated that ETR1RD is involved in phosphorylation independent signaling, implying a direct link between conformational behavior and the ability of eukaryotic receiver domains to participate in MS