Dr. Univeristy of Illinois Urbana-Champaign Urbana, Illinois
Body of Abstract: Stomatal pores regulate the exchange of CO2 and water vapor between leaves and the atmosphere. Engineering plants with lower stomatal density by over-expressing epidermal patterning factors can reduce transpiration and increase plant water use efficiency. However, the quantitative relationship between reductions in stomatal density and stomatal conductance is still poorly resolved. We aimed to address this knowledge gap while testing the anatomical and physiological plasticity of sugarcane over-expressing EPIDERMAL PATTERNING FACTOR 2 (OE-EPF2) from Sorghum bicolor. Stomatal conductance of EPF2-OE was equivalent to wild-type, despite significantly reduced stomatal density on both abaxial (-27%) and adaxial (-16%) leaf surfaces associated with reduced stomata number per file of cells. A meta-analysis of seven C3 and four C4 species revealed a correlation between engineered reductions in stomatal density and lower stomatal conductance. In C4 species, the reduction in stomatal conductance is consistently dampened relative to the reduction in stomatal density. In some C3 species, modest reductions in stomatal density are more directly proportional to reductions in stomatal conductance. In EPF2-OE sugarcane, neither stomatal-complex length, stomatal-complex width, specific leaf area, leaf nitrogen content, nor chlorophyll differed from wild-type. The absence of changes in stomatal-complex size or proxies of photosynthetic capacity suggests that greater capacity for stomatal opening likely dampens the effects of reduced stomatal density on stomatal conductance. In the future, we hope to test this hypothesis by developing the capability to assess pore size by microscopy while simultaneously controlling environmental conditions and measuring gas exchange.