Debanjana Roy (Department of Plant Sciences, UC Davis) and Maeli Melotto (Department of Plant Sciences, UC Davis)
Plants have small pores on their leaf surfaces known as stomata. These pores are formed by two kidney-shaped guard cells that serve as ports for gas exchange with the environment and plant transpiration. Pathogenic bacteria can use these pores to get inside the plant interior (intercellular space) and often scaping sanitation procedures. Plants have evolved mechanism to quickly perceive the presence of bacteria and close the stomatal pore, thus preventing leaf contamination. This phenomenon is recognized as stomatal immunity. In this study, we assessed the ability of several fresh leafy vegetables in mounting stomatal immunity against Salmonella enterica serovar Typhimurium and Escherichia coli O157:H7 and determined the influence of environmental variables on the effectiveness of the stomatal response. Butter lettuce, romaine, basil, and cilantro showed strong stomatal closure in response to O157:H7 as compared to stomatal response to the water control. Salmonella, however, induced a transient stomatal closure in butter lettuce, romaine, and basil. Unlike the other plants tested, cilantro stomata remained closed in response to Salmonella. Furthermore, air relative humidity and temperature had variable effects on the plant immunity depending on the plant-bacterium combination tested. These results indicate that the extent and the kinetics of stomatal closure and re-opening may vary among plants providing opportunities to discovering the genetic basis for stomatal immunity in plants and to proposing plant-specific control measure to reduce pathogen load on/in leafy greens.