Elevated CO2 alters xylem sap profile of amino acids and their supply rate to the shoot.
BassiriRad, Hormoz1, Sehtiya, Harbans1, 1 Department of Biological Sciences, Chicag, IL, USA
ABSTRACT- Seeds of elm were germinated and the seedlings were subsequently grown under ambient (370 ppm) and elevated (520 ppm) levels of CO2 in naturally lit greenhouses. The main objective of this study was to determine if CO2 enrichment alters xylem sap profile of various nitrogen (N) pools and their fluxes to the shoot. After 75 days of CO2 treatment, sap exudates were collected by pressurizing the intact/decapitated root systems to a hydrostatic pressure gradient of 0.5 MPa. Xylem N content was dominated by nitrate and amino acids. Fluxes of nitrate and amino acids to the shoot increased by roughly 50 and 40% respectively when plants were grown under high CO2. We measured the individual amino acids and found that the most abundant amino acids in the sap were asparagine and glutamine. Elevated CO2 significantly increased the sap concentration of these and twelve other amino acids. Furthermore, fluxes of all amino acids (except lycine) to the shoot increased in response to CO2 enrichment. This positive CO2 response ranged from 95% for glycine to only 7% for glutamate. The results have significant implications for N supply and metabolism in a CO2 enriched atmosphere.
Key words: Amino acids, Xylem sap, Elevated CO2
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