Stomatal Interactions and Emergent Behavior

Utah State University, Logan UT

Investigators

Abstract

Stomata are tiny pores on the surfaces of leaves that permit gases to diffuse between the atmosphere and the airspaces inside the plant. As such, they face the challenge of allowing ample CO2 to enter the leaf to support photosynthesis, while at the same time restricting evaporative water loss to prevent desiccation. To accomplish this, the two cells forming the pore (termed guard cells) change shape, thereby changing the pore aperture, in response to numerous environmental and physiological cues. These changes in shape result from water influx and efflux, primarily driven by ion transport processes, and occur on time scales on the order of minutes. Although each pair of guard cells responds directly to environmental cues, stomata occasionally display complex and apparently organized, non-uniform distributions of apertures, even when environmental conditions are uniform. Patches of hundreds to thousands of stomata behave differently from neighboring patches, and often this collective behavior moves about the surface of the leaf in apparently unpredictable ways. It has been proposed that such patches arise from stomatal interactions; i.e., the movements of one stoma cause neighboring stomata to move as well. These interactions have been shown to exist, but little is known of their characteristics or biological function. It has recently been suggested that stomatal patchiness might represent a form of information processing called emergent, distributed computation. Studied by computer scientists for years, emergent, distributed computation has often been proposed as a model for biological information processing. It occurs in a locally connected network of processors that solve a problem at the level of the entire network without the aid of a central controller capable of coordinating distantly separated processors. Despite the limitation of local information exchange, the solution to the problem can emerge when the processors interact such that large patches of them behave collectively. The coherent motion of such patches serves to coordinate the entire network even though there is no mechanism for doing so directly. Intriguingly, stomatal patches are statistically indistinguishable from patches associated with emergent, distributed computation, and it has been suggested that stomata may use this mode of information processing to determine the appropriate average aperture for the entire leaf. The research proposed will provide a detailed analysis of interactions among stomata to better understand how complex patterns of aperture are formed on the leaf. Known mechanisms for interaction will be characterized in detail, and new mechanisms will be investigated. The resulting data will analyzed to determine how the stomatal interactions might produce complex patterns of aperture, and to determine if these patterns are the result of distributed, emergent computation. Broader Impacts: Because stomata control the fluxes of CO2 and H2O between plants and the atmosphere, their behavior is important for plant survival, plant water use, productivity of natural and agricultural systems, and global climate modeling. All of these areas will benefit from new insights into the mechanisms controlling stomatal aperture. In addition, the research represents an unusual and provocative combination of information theory, computer science, and biology, one that holds the promise of adding novel and exciting new insights into the mechanisms by which organisms process information and respond to their environment. Perhaps most importantly, it also provides a unique opportunity for educating students across traditional disciplinary boundaries.