Root Protein Metabolism in Association with Improved Root Growth and Drought Tolerance By Elevated Carbon Dioxide in Creeping Bentgrass.

Atmospheric carbon dioxide (CO₂) concentration has been increasing and is predicted to further increase in the future along with climate changes, such as decline in water availability. Previous studies demonstrated positive effects of elevated CO₂ concentration on plant growth and tolerance to drought stress, but most examined responses of above-ground plant organs. Limited information is available on effects of elevated CO₂ concentration on root growth and the subsequent impact on plant responses to drought stress. Furthermore, the specific proteins and metabolic pathways controlling root functions regulated by CO₂ that may contribute to improved root growth and drought stress are not well understood. In this growth-chamber study with creeping bentgrass (Agrostis stolonifera), a widely-used perennial grass for forage and turf, elevated CO₂ concentration (800 µl L^-1) promoted root proliferation compared to the ambient CO₂ concentration (400 µl L^-1). Under drought stress, roots developed under elevated CO₂ concentration were able to maintain higher membrane integrity as demonstrated by lower electrolyte leakage. Proteins were extracted from roots of creeping bentgrass exposed to both elevated and ambient CO₂ concentration under well-watered and drought stress conditions. Drought- and CO₂-responsive proteins were separated with two-dimensional electrophoresis and identified using mass spectrometry. Drought- and CO₂-repsonsive proteins were mainly classified into the following functional categories: cellular structure and growth, energy, metabolism, and stress defence. The improved root growth and mitigation of drought stress in creeping bentgrass under elevated CO₂ could be mainly associated with alteration of proteins governing primary metabolism involving nitrogen metabolism, energy metabolism involving respiration, and stress defense by strengthening antioxidant metabolism and chaperone protection. Specific proteomic changes in creeping bentgrass roots due to elevated CO₂ concentration and drought stress interaction will be discussed.