Submitted to: Physiologia Plantarum
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/26/2016
Publication Date: 2/1/2017
Citation: Gleason, S.M., Wiggans, D.R., Bliss, C.A., Comas, L.H., Cooper, M.S., DeJonge, K.C., Young, J.S., Zhang, H. 2017. Coordinated decline in electron transport, PEP carboxylase activity, and maximal net CO2 assimilation with loss of hydraulic conductance during water stress in Zea mays. Physiologia Plantarum. 227:1-9. doi:10.1016/j.flora.2016.11.017.
Interpretive Summary: Maintaining productive corn plants under drought conditions is a present priority for agriculture, and will likely become more important in the future as key food producing regions become drier. Although much research has been devoted to studying specific aspects of corn biology by themselves, in this study we address the whole-plant response to drought. All the functioning components of a maize plant can be placed into three broad categories: photosynthesis, water transport, and supply of CO2. We measured the response of each of these physiological systems to drought stress in corn plants grown in a greenhouse. Similar decreases in photosynthesis and water transport where observed in plant subjected to severe levels of stress. Importantly, these responses were roughly proportional to one another, meaning that a 50% decerase in water transport corresponds to a 50% decrease in photosynthesis and plant growth. This close alignment of water transport and photosynthesis suggests that plant growth is closely coordinated with the rate of water supplied through the roots, stems, and leaves. Plant water transport recovered to ca 90% of maximal water transport values 4 d after re-watering, suggesting quick recovery of plant functioning following severe water stress. In light of these results, possible strategies for improving the species are discussed.
Technical Abstract: Maintaining high photosynthetic yield in water-stressed maize plants is a present priority for agriculture, and will likely increase in importance as key food producing regions become drier in the future. Although several physiological responses to water stress in maize have been studied in isolation, we address here the whole-plant response to water stress and ask: what are the key physiological failures that occur in maize and how do these failures correlate with reductions in net CO2 assimilation? Xylem conductance, whole-plant conductance, stomatal conductance, rate of electron transport (ETR), maximal catalytic rate of phosphoenolpyruvate carboxylase (Vpmax), and net CO2 assimilation (Anet) were measured in maize plants subjected to contrasting levels of water stress in a greenhouse during their vegetative phase of growth. Plants were dried down gradually to assess the entire range of physiological response to decreasing leaf water potential ('leaf). Photosynthesis (ETR, Vpmax) decreased proportionately and significantly with 'leaf, exhibiting a decline of 80% at the end of the dry-down ('leaf ~ 4.0 MPa). These reductions in photosynthetic functioning were closely aligned with similar reductions in whole-plant conductance and stem xylem conductance. Close alignment among xylem, photosynthetic, and stomatal functioning suggest that enzyme activity and CO2 supply are closely coordinated with the rate of water supplied through the xylem. Whole-plant transpiration rates recovered to ca 90% of maximal values 4 d after re-watering, suggesting quick recovery of xylem functioning following severe water stress ('leaf ~ -4 MPa). Possible strategies for improving the species may include reduced stomatal sensitivity to internal and external cues, as well as xylem that is less susceptible to damage at low 'leaf.