Early Warning Signs of Plant Stress

The Science

As environmental conditions change around the world, farmers look to science to know when to intervene to protect plants, particularly under stress caused by drought. Plant metabolism may change before external signs like photosynthesis rates, shedding of leaves, or slower growth are evident, but monitoring metabolism didn’t seem practical. In this research, scientists studied how the composition, structure, and function of cell walls in California poplars changed under drought conditions. They discovered that esters—organic compounds that react with water to produce alcohols like methanol and acids like acetic acid—seemed to hold the key. The changing ratio of acetic acid and methanol the plants gave off could provide the best first clue that drought was affecting a plant. This change in ratio reduced growth rates while activating the plant’s drought defenses.

The Impact

Around the world, fast-growing trees like California poplars provide a sustainable source of bioproducts and biofuels. They are also used to fix carbon in the soil, offer green spaces in urban environments, stabilize hillsides, and restore forests. Unfortunately, recent droughts in various countries have led to massive die offs. For example, one poplar forest in Northern China saw as much as a 79% loss in 2018. Understanding the biological mechanisms and environmental thresholds that determine plant response to drought stress is critical for identifying which trees are in danger and their physical responses to stress.

Summary

Fast-growing trees such as California poplar are of interest to the Department of Energy (DOE) as sustainable sources of biofuels and bioproducts. However, poplars under drought stress often lose leaves, grow more slowly, and have lower rates of photosynthesis than those growing under more favorable conditions. To keep such plants healthy, researchers needed to understand the metabolic processes in the cells of these plants. A multi-institutional team of scientists first identified patterns in active growth at the cellular level among potted California poplars and determined that the cell wall played a larger role than previously thought. They then increased the temperature and reduced the amount of water the plants received to induce drought conditions. Using advanced nuclear magnetic resonance instruments at EMSL, the Environmental Molecular Sciences Laboratory, a DOE Office of Science user facility, they measured changes in cell wall composition, function, and structure. They found that, as temperatures increased and plants became more stressed, cell walls gave off a much larger ratio (400 to 3,500 percent) of acetic acid and methanol. This change was evident regardless of whether samples were taken from leaves, branches, or detached stems. Monitoring atmospheric levels of acetic acid/methanol emissions could prove to be a highly sensitive signal for these plants when they are under drought stress, but before more advanced signs of such stress are present.

Contacts

Kolby Jardine, Lawrence Berkeley National Laboratory,kjjardine@lbl.gov

Robert Young, Environmental Molecular Sciences Laboratory,robertyoung@pnnl.gov

Funding

This work was supported by the DOE Office of Science, Biological and Environmental Research program through the Early Career Research Program, and by the DOE Joint BioEnergy Institute. A portion of the research was performed on project awards from EMSL, the Environmental Molecular Sciences Laboratory, a DOE Office of Science user facility.

Publication

K.J. Jardine, et al., “Cell wall ester modifications and volatile emission signatures of plant response to abiotic stress.” Plant, Cell and Environment 45, 3429 (2022). [DOI: 10.111/pce.14464]