Quantitative effects of environmental variation on stomatal anatomy and gas exchange in a grass model

Stomata are cellular pores on the leaf epidermis that allow plants to regulate carbon assimilation and water loss. Stomata integrate environmental signals to regulate pore apertures and optimize gas exchange to fluctuating conditions. Here, we quantified intraspecific plasticity of stomatal gas exchange and anatomy in response to seasonal variation in Brachypodium distachyon. Over the course of two years we (i) used infrared gas analysis to assess light response kinetics of 120 Bd21-3 wild-type individuals in an environmentally fluctuating greenhouse and (ii) microscopically determined the seasonal variability of stomatal anatomy in a subset of these plants. We observed systemic environmental effects on gas exchange measurements and remarkable intraspecific plasticity of stomatal anatomical traits. To reliably link anatomical variation to gas exchange, we adjusted anatomical gsmax calculations for grass stomatal morphology. We propose that systemic effects and variability in stomatal anatomy should be accounted for in long-term gas exchange studies.

Duplicated antagonistic EPF peptides optimize grass stomatal initiation

Peptide signaling has emerged as a key component of plant growth and development, including stomatal patterning, which is critical for plant productivity and survival. Although exciting progress has been made in understanding EPIDERMAL PATTERNING FACTOR (EPF) signaling in Arabidopsis, the mechanisms by which EPF peptides control different stomatal patterns and morphologies in grasses is poorly understood. Here, by examining expression patterns, overexpression transgenics, and cross-species complementation, the antagonistic stomatal ligands orthologous to Arabidopsis AtEPF2 and AtSTOMAGEN/AtEPFL9 peptides were identified in Triticum aestivum(wheat) and the grass model organism Brachypodium distachyon. Application of bioactive BdEPF2 peptides inhibited stomatal initiation, but not the progression or differentiation of stomatal precursors in Brachypodium. Additionally, the inhibitory roles of these EPF peptides during grass stomatal development were suppressed by the contrasting positive action of the BdSTOMAGEN peptide in a dose-dependent manner. These results not only demonstrate how conserved EPF peptides that control different stomatal patterns exist in nature but also suggest new strategies to improve crop yield through the utilization of plant-derived antagonistic peptides that optimize stomatal density on the plant epidermis.

Transcriptional regulation of ZIP genes is independent of local zinc status in Brachypodium shoots upon zinc deficiency and resupply

The biological processes underlying zinc homeostasis are targets for genetic improvement of crops to counter human malnutrition. Detailed phenotyping, ionomic, RNA-Seq analyses and flux measurements with 67Zn isotope revealed whole plant molecular events underlying zinc homeostasis upon varying zinc supply and during zinc resupply to starved Brachypodium distachyon (Brachypodium) plants. Although both zinc deficiency and excess hindered Brachypodium growth, accumulation of biomass and micronutrients into roots and shoots differed depending on zinc supply. The zinc resupply dynamics involved 1893 zinc-responsive genes. Multiple ZIP transporter genes and dozens of other genes were rapidly and transiently down-regulated in early stages of zinc resupply, suggesting a transient zinc shock, sensed locally in roots. Notably genes with identical regulation were observed in shoots without zinc accumulation, pointing to root-to-shoot signals mediating whole plant responses to zinc resupply. Molecular events uncovered in the grass model Brachypodium are useful for the improvement of staple monocots.

Building a hybrid DEVS and GRASS model using a composable cellular automaton

Modeling and simulation is pervasive throughout many different disciplines. As computing technology has provided more capability, the systems being modeled and simulated have grown larger and more complex. Often times, these large systems are managed as interacting subsystems. When it is necessary for the simulation to allow disparate subsystems to maintain their independence, then a hybrid model of the subsystems should be used. Furthermore, to ease the burden of verification and validation of simulation results, a proven system theoretical modeling specification should be used. However, many communities have already adopted nonsystem theoretical software solutions and established a group of domain experts familiar with these tools. This paper provides two things: a formal approach to building a hybrid model, and a discussion of how to incorporate a nonsystem theoretical software implementation into a proven framework. The first is done through the implementation of a Knowledge Interchange Broker (KIB) as an Interaction Model (IM). The second is accomplished by exemplifying the use of the IM in an agent-environment hybrid model. In the hybrid model, the agent is implemented in the Discrete-event System (DEVS) specification and the environment is implemented in the Geographical Resources Analysis Support System (GRASS) using a Composable Cellular Automaton (CCA) specification. This concept has been successfully applied to both example models and an interdisciplinary research project where the interactions between human activities and landscape processes are studied.

Adapting the CATIMO grass model to meadow bromegrass grown in western Canada

Bonesmo, H., Baron, V. S., Young, D., Bélanger, G. and Jing, Q. 2014. Adapting the CATIMO grass model to meadow bromegrass grown in western Canada. Can. J. Plant Sci. 94: 61–71. The Canadian Timothy Model (CATIMO) simulates the growth and nutritive value of timothy grown in eastern and western Canada, Norway, and Finland, but has not been parameterized for meadow bromegrass (Bromus riparius Rehm.) grown under Canadian prairie conditions. We parameterized and evaluated the CATIMO model to simulate the dry matter (DM) yield and N concentration of meadow bromegrass grown in western Canada with data from sequential sampling in primary growth and regrowth from two field experiments for a total of 5 yr of observation. Primary growth DM yield was simulated well [R2=0.95; normalized root mean square error (NRMSE) =16%; model simulation efficiency (EF)=0.93]. Simulations of the regrowth DM yield (R2=0.49, NRMSE=39%, EF=0.47) were not as successful as that of the primary growth, but they were within expected ranges for regrowth DM yields in western Canada. Forage N concentration was poorly simulated in primary growth (R2=0.32, NRMSE=38%, EF=−0.95) and regrowth (R2=0.27, NRMSE=30%, EF=−2.43). Plant-available soil moisture down to 30 cm was simulated well (R2=0.74, NRMSE=19%, EF=0.50). The parameterized model for meadow bromegrass expands the use of the CATIMO model to drier geographical areas where timothy may not be common, and it represents a first attempt to provide DM yield assessment of meadow bromegrass under Canadian Prairie conditions for whole-farm modeling.