Submitted to: Photosynthetica
Publication Type: Peer reviewed journal
Publication Acceptance Date: 5/7/2014
Publication Date: 3/4/2015
Citation: Sicher, Jr., R.C., Bunce, J.A., Barnaby, J.Y., Bailey, B.A. 2015. Water-deficiency effects on single leaf gas exchange and on C4 pathway enzymes of maize genotypes with differing abiotic stress tolerance. Photosynthetica. 53:3-10. Interpretive Summary: Unlike most crop plants, maize leaves possess a unique biochemical carbon dioxide concentrating mechanism that saturates rates of photosynthesis in normal air and endows maize with improved water use efficiency. However, there is a growing perception that the carbon dioxide pump can break down when maize plants are exposed to water stress. In the current study, we examined how components of the carbon dioxide pump functioned in response to drought using three maize lines that were previously shown to be susceptible or resistant to water stress. Results showed that the carbon dioxide pump was inhibited by drought but did not change as much as the overall photosynthetic rate. Also, the carbon dioxide concentrating mechanism was less affected by drought in the stress tolerant lines. These results should benefit agronomists, physiologists, and geneticists working with maize. Also, these findings should help scientists constructing crop simulation models to accurately model water stress.
Technical Abstract: Responses to drought were studied using two maize inbred lines (B76 and B106) and a commercial maize hybrid (Zea mays L. cv. Silver Queen) with differing resistance to abiotic stress. Maize seedlings were grown in pots in controlled environment chambers for 17 days and watering was withheld from one half the plants for an additional 11 days. On the final treatment date, leaf water potentials did not differ among genotypes and were -0.84 and -1.49 MPa in the water sufficient and insufficient treatments, respectively. The effects of water stress on rates of CO2 assimilation (A) differed for the stress tolerant maize inbred line, B76, (P = 0.01) when compared to the other two genotypes. Also, rates of A for all three genotypes were unaffected when the measurement O2 concentration was decreased for 21 to 2% (v/v). Activities of three enzymes in the C4 photosynthetic pathway were inhibited from 25 to 49% due to water stress, when averaged across genotypes. Unlike the other enzyme steps, genotypic differences were not observed for water stress effects on the activity of NADP-malic enzyme. Gene expression was determined for three C4 pathway enzymes in the three maize genotypes. Transcript levels were unchanged or increased in response to water stress for seven out of nine measurements. Examples where transcripts decreased due to drought were associated with the two stress susceptible genotypes. The above results suggested that the C4 photosynthetic pathway was less inhibited by drought in stress tolerant compared to stress susceptible maize genotypes.