Long-term in vivo observation of maize leaf xylem embolism, transpiration and photosynthesis during drought and recovery

Authors: Allen, Brendan; STEWART, JARED - Collaborator; Polutchko, Stephanie; OCHELTREE, TROY - Colorado State University; Gleason, Sean

Submitted to: Plant Cell and Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/18/2025
Publication Date: 2/3/2025
Citation: Allen, B.S., Stewart, J.J., Polutchko, S.K., Ocheltree, T.W., Gleason, S.M. 2025. Identifying critical thresholds for maize drought stress and recovery. Plant Cell and Environment. 48(6):4114-4125. https://doi.org/10.1111/pce.15414.
DOI: https://doi.org/10.1111/pce.15414

Interpretive Summary: Plants need to move water from the soil to the sites of photosynthesis in the leaves to grow. This water transport happens through xylem tubes, which operate under negative pressure. When plants are stressed by lack of water, the pressure in the xylem can become too low, causing air bubbles (embolism) to form and block the water flow. These blockages can permanently damage plants, especially after a drought. Studying xylem in crops is difficult because invasive methods can give inaccurate results. Our study uses non-invasive optical methods to track when emboli form and see if plants can repair/refill emboli after they occur. We focused on maize leaves and watched for embolism and leaf shrinkage during severe dryness in a controlled setting. By monitoring gas exchange, chlorophyll fluorescence, and whole plant water loss, we identified the order of physiological failures leading to leaf death. We found that recovery from extreme water stress depends on how much embolism has built up. Major veins with embolism do not refill, and full embolism in leaves leads to leaf death. Understanding these relationships will help improve crop productivity and resilience in changing environments.

Technical Abstract: Plant water transport is essential to maintain turgor, photosynthesis and growth. Water is transported in a metastable state under large negative pressures, which can result in embolism, that is, the loss of function by the replacement of liquid xylem sap with gas, as a consequence of water stress. To avoid experimental artefacts, we used an optical vulnerability system to quantify embolism occurrence across six fully expanded maize leaves to characterize the sequence of physiological responses (photosynthesis, chlorophyll fluorescence, whole-plant transpiration and leaf inter-vein distance) in relation to declining water availability and leaf embolism during severe water stress. Additionally, we characterize the recovery of leaf function in the presence of sustained embolism during a 6-day recovery period. Embolism formation occurred after other physiological processes were substantially depressed and were irreversible upon rewatering. Recovery of transpiration, net CO2 assimilation and photosystem II efficiency were aligned with the severity of embolism, whereas these traits returned to near pre-stress levels in the absence of embolism. A better understanding of the relationships between embolism occurrence and downstream physiological processes during stress and recovery is critical for the improvement of crop productivity and resilience.