Effects of Bacterial Endophytes on Carbon Partitioning and Water Potential in Sunflower Plants.

The demand for efficient and sustainable agricultural crop growth has increased with growing world populations. Recent studies have shown that bacterial endophytes, microorganisms living symbiotically within plants, may alleviate resource limitations by fixing supplemental nitrogen from the atmosphere. This dinitrogen is allocated to the plant in exchange for photosynthetically fixed carbon, altering source-sink relationships within the plant system. The change in substrate flow may also affect water movement in the plant by shifting osmotic potential. The purpose of this study was to investigate the effects of bacterial endophytes on: 1) partitioning of photosynthetically fixed carbon within the whole plant, and 2) leaf water potential. Sunflowers (Helianthus annuus) were inoculated with WP5 (Rahnella sp. CDC 298779), a bacterial endophyte strain isolated from wild poplar (Populus trichocarpa), and grown in a controlled environment. ¹³CO₂ pulse labeling was applied to one mature leaf of each plant (from both inoculated and control groups); leaf, stem, and root tissues were then analyzed for δ¹³C content. Osmotic potential was measured using a psychrometer and reflectometer. Nitrogen content, photosynthetic capacity, and biomass were also measured. The expected results: in inoculated plants, carbon will be partitioned locally to support endophyte colonies in the target leaf, subsequently decreasing osmotic potential in apoplastic cellular spaces. Gaining a more detailed understanding of endophyte-plant interactions may have profound impacts on agricultural practices and inform resource management.