Tracer Advection in an Idealised River Bend with Groynes

This paper presents numerical simulations of particle advection in the bend of an open channel containing groynes, which is an idealised form of a shallow river bend in a wide river. The flow field is computed using a boundary-fitted solver of the non-orthogonal, curvilinear shallow water equations. The computational grid is generated by solving Poisson-type elliptic partial differential equations using an iterative multi-grid scheme for prescribed boundary coordinates. The shallow water equations are discretised with finite differences in space, and 4th order Runge-Kutta integration in time. Tracers introduced at specific initial locations have their trajectories computed using Lagrangian particle tracking. The numerical shallow flow model is verified by comparison to the analytical solution of fully developed flow in an open channel. The combined shallow flow and Lagrangian particle-tracking model is then used to simulate the advection of tracer particles in a rectangular channel containing a pair of parallel groynes, and tracer particles in a curved open channel containing groynes, of dimensions roughly equivalent to a Danube River bend

Promotion of testa rupture during garden cress germination involves seed compartment-specific expression and activity of pectin methylesterases

Pectin methylesterase (PME) controls the methylesterification status of pectins and thereby determines the biophysical properties of plant cell walls, which are important for tissue growth and weakening processes. We demonstrate here that tissue-specific and spatiotemporal alterations in cell wall pectin methylesterification occur during the germination of garden cress (Lepidium sativum). These cell wall changes are associated with characteristic expression patterns of PME genes and resultant enzyme activities in the key seed compartments CAP (micropylar endosperm) and RAD (radicle plus lower hypocotyl). Transcriptome and quantitative real-time reverse transcription-polymerase chain reaction analysis as well as PME enzyme activity measurements of separated seed compartments, including CAP and RAD, revealed distinct phases during germination. These were associated with hormonal and compartment-specific regulation of PME group 1, PME group 2, and PME inhibitor transcript expression and total PME activity. The regulatory patterns indicated a role for PME activity in testa rupture (TR). Consistent with a role for cell wall pectin methylesterification in TR, treatment of seeds with PME resulted in enhanced testa permeability and promoted TR. Mathematical modeling of transcript expression changes in germinating garden cress and Arabidopsis (Arabidopsis thaliana) seeds suggested that group 2 PMEs make a major contribution to the overall PME activity rather than acting as PME inhibitors. It is concluded that regulated changes in the degree of pectin methylesterification through CAP- and RAD-specific PME and PME inhibitor expression play a crucial role during Brassicaceae seed germination

HRS1 Acts as a Negative Regulator of Abscisic Acid Signaling to Promote Timely Germination of Arabidopsis Seeds

In this work, we conducted functional analysis of Arabidopsis HRS1 gene in order to provide new insights into the mechanisms governing seed germination. Compared with wild type (WT) control, HRS1 knockout mutant (hrs1-1) exhibited significant germination delays on either normal medium or those supplemented with abscisic acid (ABA) or sodium chloride (NaCl), with the magnitude of the delay being substantially larger on the latter media. The hypersensitivity of hrs1-1 germination to ABA and NaCl required ABI3, ABI4 and ABI5, and was aggravated in the double mutant hrs1-1abi1-2 and triple mutant hrs1-1hab1-1abi1-2, indicating that HRS1 acts as a negative regulator of ABA signaling during seed germination. Consistent with this notion, HRS1 expression was found in the embryo axis, and was regulated both temporally and spatially, during seed germination. Further analysis showed that the delay of hrs1-1 germination under normal conditions was associated with reduction in the elongation of the cells located in the lower hypocotyl (LH) and transition zone (TZ) of embryo axis. Interestingly, the germination rate of hrs1-1 was more severely reduced by the inhibitor of cell elongation, and more significantly decreased by the suppressors of plasmalemma H+-ATPase activity, than that of WT control. The plasmalemma H+-ATPase activity in the germinating seeds of hrs1-1 was substantially lower than that exhibited by WT control, and fusicoccin, an activator of this pump, corrected the transient germination delay of hrs1-1. Together, our data suggest that HRS1 may be needed for suppressing ABA signaling in germinating embryo axis, which promotes the timely germination of Arabidopsis seeds probably by facilitating the proper function of plasmalemma H+-ATPase and the efficient elongation of LH and TZ cells

On the characteristics of velocities fields on the vicinity of manhole inlet grates during flood events

The accurate characterisation of flow from urban surfaces to sewer/stormwater systems is important for urban drainage design and flood modelling/risk identification. However, the geometrical complexity and large variety of drainage structures (linking elements) available makes model calibration and verification difficult. In this study an extensive comparison between experimentally measured and numerically modelled flow characteristics in the vicinity of ten different designs of manhole grate was performed under drainage flow in sub‐critical conditions. Using a 2D surface PIV (sPIV) system the work presents the first detailed characterisation of velocity fields around these linking elements. In addition, it provides the first detailed verification of the ability of a 2D numerical model to describe both velocity fields and drainage flows. The overall comparison shows a close relationship between numerical and the experimental results with some higher inflows in the experimental results as a consequence of a localised transition from weir to orifice condition near the void areas of the grates. It was also noted that velocity differences decreased further from the manhole, due mainly to the more directional flow. Overall the work demonstrates the potential for further use of 2D numerical models to describe flow conditions at linking elements, either directly within modelling simulations or indirectly via the characterisation of energy loss coefficients