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 the climatic changes which may increase evaporative demand on plants. Elevated CO2 concentration has a positive effect on plant growth and tolerance to drought stress with regard to above-ground plant organs but limited information is available describing effects of elevated CO2 concentration on root growth and the subsequent impact on plant responses to drought stress. The specific proteins and metabolic pathways controlling root functions regulated by CO2 that may contribute to improved root growth and drought stress damages are not well understood. In this study with creeping bentgrass (Agrostis stolonifera cv. Penncross), 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 improved 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. Root proteins were mainly classified into the following functional categories: cellular growth, energy, metabolism, and 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 (glutamine synthetase), energy metabolism involving respiration (glyceraldehyde-3-phosphate dehydrogenase), and stress defence by strengthening antioxidant metabolism (ascorbate peroxidase, superoxide dismutase, and catalase) and chaperone protection (HSP81-1).