Effects of CO2 enrichment on soluble amino acids and organic acids in barley primary leaves as a function of age, photoperiod, and chlorosis

Authors: Sicher Jr, Richard

Submitted to: Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/1/2008
Publication Date: 6/3/2008
Citation: Sicher Jr, R.C. 2008. Effects of CO2 enrichment on soluble amino acids and organic acids in barley primary leaves as a function of age, photoperiod, and chlorosis. Plant Science. 174:576-582.

Interpretive Summary: This study investigated the effects of rising atmospheric carbon dioxide on the nitrogen nutrition of barley leaves. Earlier studies established that plants grown in elevated carbon dioxide contained high levels of carbohydrates but low levels of protein. Proteins have an important role in photosynthesis and are high in nitrogen. At this time scientists do not know why growth in elevated carbon dioxide decreases the protein content of leaves. This report demonstrated that amino acid levels decreased in barley leaves in response to carbon dioxide enrichment. This is important because amino acids are needed to manufacture proteins in leaves. This finding suggested that carbon dioxide enrichment decreased the ability of barley leaves to manufacture amino acids. This research will be of interest to cereal scientists, physiologists, biochemists, and geneticists studying the effects of environmental change on crop plants.

Technical Abstract: Responses of soluble amino acids and organic acids to CO2 enrichment were determined using barley primary leaves (Hordeum vulgare L. cv. Brant). Plants were grown in controlled environment chambers using either ambient (36 Pa) or elevated (100 Pa) CO2 treatments. Total soluble amino acids were increased by CO2 enrichment 9 days after sowing (DAS) but decreases relative to the ambient CO2 treatment, particularly for glutamine and asparagine, were observed 13 and 17 DAS. It was concluded that CO2 dependent leaf yellowing negatively impacted soluble amino acid levels in older barley primary leaves. In contrast to the ambient CO2 treatment, glutamine decreased progressively by over 60% during the first 12 h of the light period in primary leaves of 13 d old plants grown under enhanced CO2. These decreasing glutamine levels in the light were attributed to inadequate rates of N uptake and assimilation in the elevated CO2 treatment. Malate was decreased about 10 to 20 percent by CO2 enrichment and citrate and succinate were increased by a like amount when measured 9 and 13 DAS. The onset of CO2 dependent leaf yellowing had much less of an effect on organic acids than on soluble amino acids in barley primary leaves. This result emphasized the sensitivity of N assimilation to CO2 enrichment in barley. Increased levels of citrate and succinate in response to CO2 enrichment suggested that the tricarboxylic acid cycle was upregulated by CO2 enrichment. In summary, organic and amino acid levels in barley primary leaves were dynamic and were altered by age, diurnally and in response to CO2 enrichment. Moreover, changes of amino acids and organic acids in barley primary leaves with age and diurnally were poorly correlated with that of major nonstructural carbohydrates.