ARS | Publication request: Impact of carbon dioxide enrichment on the responses of maize leaf transcripts and metabolites to water stress

Submitted to: Physiologia Plantarum
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 23, 2011
Publication Date: March 3, 2012
Citation: Sicher Jr, R.C., Barnaby, J.Y. 2012. Impact of carbon dioxide enrichment on the responses of maize leaf transcripts and metabolites to water stress. Physiologia Plantarum. 144:238-253.

Interpretive Summary: Water consumption rates of field crops decrease when carbon dioxide increases in the atmosphere. This is significant because water availability is a major factor determining maize yields. The objective of this investigation was to measure the combined effects of carbon dioxide levels in the atmosphere and drought on maize. Changes of thirty-six individual small molecules in maize leaves were measured over several days after drought treatments were imposed. These leaf constituents were involved in basic processes affecting maize growth and development. Our results showed that elevated carbon dioxide lessened the effects of drought on some maize processes and not others. This finding demonstrates that the approach of measuring multiple small molecules in maize is a powerful tool for identifying which processes in maize leaves adjust in response to drought and why. This is also a potentially game changing approach for understanding interactions between atmospheric carbon dioxide and complex stress events in plants. This manuscript will be of value to many scientists and government policymakers interested in environmental change and agriculture.

Technical Abstract: Maize (Zea mays L.) was grown in controlled environment chambers with ambient (38 Pa) and elevated (70 Pa) CO2. Drought treatments were imposed 17 days after sowing by withholding nutrient solution from one half the plants in each CO2 treatment. Decreases of total leaf water potential, net CO2 assimilation and stomatal conductance in response to drought were diminished by CO2 enrichment. Decreases of leaf nitrate with increasing plant age were accelerated by drought but this was unaffected by CO2 enrichment. Levels of 36 maize leaf metabolites were monitored in response to drought and 21 of these changed 2 fold or more. All of eight soluble carbohydrates increased with drought under ambient CO2, whereas only glucose, fructose and raffinose changed in the elevated CO2 treatment. Aconitate and shikimate increased 5 to 15 fold and malate, fumarate and 2-oxoglutarate decreased over 80% in response to drought. Conversions of succinate to fumarate were likely blocked by drought. Serine, glycine and proline were prominent amino acids that increased due to drought. This suggested that drought inhibited the C4 photosynthetic pathway and induced phenylpropanoid metabolism. Alanine, aspartate and apsaragine decreased almost to zero in water insufficient compared to sufficient plants. Except for the latter three amino acids elevated carbon dioxide delayed, diminished or abolished changes of leaf metabolites in response to drought. This was likely due to increased leaf water potential. Drought dependent changes of N containing compounds not mitigated by carbon dioxide enrichment were attributed to limiting inorganic nitrogen rather than to water insufficiency.