Document: DAV-3-34-38

Elevated CO₂ alters amino acid profiles in wheat leaves.

SMART, D.R.*, D.NGUYEN, N.TRINH and A.J.BLOOM

University of California, Davis, CA 95616 ¹

Abstract:
C₃ plants grown under elevated CO₂ concentrations generally have lower organic nitrogen contents than C₃ plants grown under ambient CO₂. A popular hypothesis thought to best explain these results proposes that Rubisco levels decline when CO₂ concentration is increased. Support for the above hypothesis has been inconsistent. Elevated CO₂ decreases oxygen fixation by Rubisco, thus diminishing carbon flux through the oxidative C₂ pathway and nitrogen flux through the photorespiratory nitrogen cycle. Such an effect may decrease the levels of NH₄⁺, glycine and serine, and raise or lower other amino acid levels. Such an effect may also influence protein content. We made a preliminary examination of this hypothesis by assembling total physiologic and hydrolyzed amino acid profiles for wheat plants grown under elevated and ambient CO₂. Ammonium, glycine and serine levels under elevated CO₂ did not decrease to a level that was statistically significantly lower (P > 0.05) than the levels observed under ambient CO₂. In addition, the levels of glutamate, glutamine, aspartate and asparagine, amino acids involved in N transport and the majority of transamination reactions, were unaffected by CO₂ concentration. The most consistent effect was an increase in asparagine, glutamine, and alanine when NH₄⁺ was the N-source, and a trend where several amino acid concentrations decreased in elevated CO₂ when NO₃^- was the N-source. Our results may best support that inhibition of NO₃^- assimilation by elevated CO₂ causes protein contents to decline.

Keywords: Elevated CO₂, protein content, amino acid, NO₃^- assimilation.

This abstract is being presented at: 10:30 AM in session:
Poster Session #18: Elevated CO₂.