The OnGuard platform enables quantitative systems dynamic modelling of the stomatal guard cell. It incorporates explicitly all of the fundamental properties for transporters at the plasma membrane and tonoplast, the salient features of osmolyte metabolism, and the major controls of cytosolic-free calcium concentration and pH. OnGuard takes a structured approach to tier and interrelate elements, and gives ready access to parameters and equations ‘on the fly’ while enabling the network of components within each model to interact computationally.
With OnGuard2-CRR (Version 18.104.22.168, April 2019), the platform incorporates evapotranspiration and the water relations of the whole plant. The Constraint-Relaxation-Recovery extension allows for solute release and recovery by the surrounding epidermal cells that impose a turgor constraint on guard cell expansion. Models built on this platform accommodate all aspects of stomatal transpiration with outputs for stomatal conductance as well as aperture and guard cell osmotic content. As in previous versions, an optional cartoon display is available that provides a schematic representation of a guard cell pair, showing in runtime the changes in stomatal aperture, along with selectable trans-membrane transporter and solute fluxes.
OnGuard2-CRR is freely available for download. Users are required to register the software on installation. The platform is an expert system. Effective use requires a good working knowledge of guard cells, transport physiology, and some familiarity with current-voltage curves. When publishing simulations and analysis using the software, please cite the following three articles:
Adrian Hills, Zhonghua Chen, Anna Amtmann, Michael R. Blatt and Virgilio L. Lew: “On-Guard: A Computational Platform for Quantitative Kinetic Modeling of Guard Cell Physiology.” Plant Physiology, 2012, 159:1026–1042.
Zhonghua Chen, Adrian Hills, Ulrike Bӓtz, Anna Amtmann, Virgilio L. Lew and Michael R. Blatt: “Systems Dynamic Modeling of the Stomatal Guard Cell Predicts Emergent Behaviors in Transport, Signaling and Volume Control.” Plant Physiology, 2012, 159:1235–1251.
Yizhou Wang, Adrian Hills, Silvere Vialet-Chabrand, Maria Papanatsiou, Howard Griffiths, Simon Rogers, Tracy Lawson Virgilio L. Lew, and Michael R. Blatt: “Unexpected connections between humidity and ion transport discovered using a model to bridge guard cell-to-leaf scales. Plant Cell 2017 29:2921-2939
Mareike Jezek, Adrian Hills, Michael R. Blatt, and Virgilio L. Lew: A constraint-relaxation-recovery mechanism for stomatal dynamics. Plant Cell and Environment 2019, in press.
OTHER THINGS YOU NEED TO KNOW
* Direct and easy access to all model parameters, and facility to define solute compositions, transporter populations, biophyical and kinetic parameters.
* Automatic ‘smart’ time base that accelerates computational speed with minimum and maximum limits.
* A Reference State Wizard that aids establishing stable models.
* Simulation-time graphical display of current-voltage relations for transporters at both membranes.
* Simulation-time tabular display of all ionic and other solute contents for each compartment and fluxes between compartments, tabular display of related variables.
* Simulation-time graphical chart recorder of key variable outputs.
* Logging of all variables in spreadsheet-readable (*.csv) format.
*OnGuard2 is supplied with model parameter (*.obg) files for wild-type Arabidopsis stomata, and for the slac1 and ost2 mutants.
Pentium V or better CPU, running Microsoft Windows Vista or Windows 7; Administrator rights to install the package. We recommend a quad processor system for best results.