Submitted to: International Journal of Agronomy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/11/2012
Publication Date: 8/10/2012
Citation: Sicher, Jr., R.C. 2012. Responses of metabolites in soybean shoot apices to changing atmospheric carbon dioxide concentrations. International Journal of Agronomy. DOI: ORG/10.1155/2012/309153. Interpretive Summary: Atmospheric carbon dioxide concentrations will double by the end of this century and it is important to determine how crop plants will be affected by this development. Carbon dioxide is essential for plant growth and also contributes to global warming. Most plant studies have examined the effects of carbon dioxide enrichment on leaves. The current study investigated how plant growth in elevated carbon dioxide altered chemical compounds within the soybean apex. The apex is the growing tip on the plant and tissues within the apex control shoot growth and development. Two important plant sugars, sucrose and fructose, were increased up to 40% and an unidentified compound was decreased by 50 to 80% in the soybean apex by plant growth in elevated carbon dioxide. Moreover, only a handful of plant constituents in the shoot apex were affected by elevated carbon dioxide treatments. It is possible that the three compounds identified in this study function in regulating plant development. These results should be of interest to scientists studying plant development, the effects of global change on agriculture, and to government policy makers and plant breeders.
Technical Abstract: Soybean seedlings were grown in controlled environment chambers with chamber air CO2 partial pressures of 38 (ambient) and 72 (elevated) Pa. Samples were collected 21 to 24 days after sowing by harvesting five or six apices from the main shoot and from lateral branches on a single plant. Metabolites from soybean apices were analyzed by gas chromatography and results indicated that two out of 21 compounds, i.e., sucrose and fructose, increased in response to CO2 enrichment. An unidentified metabolite, Unk-21.03, that was observed on the total ion chromatogram between malate and aspartate, decreased up to 80% in soybean apices in response to the elevated CO2 treatment. Levels of Unk-21.03 decreased progressively as atmospheric CO2 partial pressures used for plant growth were increased from 26 to 100 Pa. Reciprocal transfer experiments showed that changes of Unk-21.03 and sucrose in soybean apices occurred over several days in response to a change in CO2 partial pressure. This suggested that, like sucrose, Unk-21.03 was synthesized elsewhere on the plant and was transferred to the apex. The mass spectrum of Unk-21.03 suggested that this compound contained both an amino and carboxyl group and was related to serine or aspartate. None of the other amines in this study were affected by CO2 enrichment indicating that nitrogen was not limiting for plant growth. The above results showed that less than 10% of the compounds in soybean apices were increased by CO2 enrichment and this was restricted to two major soluble carbohydrates. Identifying Unk-21.03 and understanding how CO2 enrichment affected levels of this compound in soybean apices could be an important step in adapting terrestrial plants to future atmospheres enriched with CO2.