Serendipitous Discovery: Transforming Seedlings into Superior Plants with an Uncommon Chemical Exposure

Exposing seeds to specific chemicals during their seed stage, a process known as ‘priming,’ can significantly influence their later growth.

A novel finding by researchers reveals that ethylene gas treatment of seeds enhances their growth and resistance to stress. This finding, highlighting improved photosynthesis and carbohydrate generation in plants, represents a potential leap forward in boosting agricultural productivity and resilience to environmental challenges.

Plants, like all organisms, are susceptible to stress, commonly from heat or drought, which can stunt their growth or reduce yield. This poses challenges for agriculture, prompting efforts to genetically engineer more robust plants.

However, plants engineered for higher yields often show reduced stress tolerance due to their energy allocation toward growth over stress defense. Conversely, enhancing stress resilience can lead to diminished growth. This dilemma complicates efforts to elevate agricultural output.

My research has been centered on how the plant hormone ethylene influences plant growth and stress response. In a study published in July 2023, my laboratory made a surprising and promising observation. We discovered that germinating seeds in the dark, a common underground occurrence, respond positively to ethylene exposure, showing increased growth and stress tolerance.

Ethylene: A Key Plant Hormone

Plants, immobilized by nature, cannot evade stressful environmental conditions like heat and drought. They perceive various environmental signals, including light and temperature, influencing their growth, development, and stress management. Ethylene, a critical hormone in this regulatory network, aids plants in adapting to their environment.

First identified over a century ago as a gaseous plant hormone, ethylene is produced by all land plants studied to date. It plays roles beyond growth and stress response, including leaf color changes in autumn and fruit ripening.

Utilizing Ethylene to ‘Prime’ Plants

Our laboratory specializes in understanding how plants and bacteria detect ethylene and its interaction with other hormone pathways in plant development. During our research, we stumbled upon an unexpected discovery.

In an experiment involving seed germination in darkness, we exposed seeds to ethylene gas for several days before removing it. Usually, our experiments would conclude at this stage. However, after collecting data, we moved the seedlings to a light cart, aiming to grow adult plants for future seed harvesting.

A few days later, we observed that the seedlings briefly exposed to ethylene were considerably larger, with more expansive leaves and more intricate root systems, compared to unexposed plants. This accelerated growth persisted throughout their lifespan.

The image compares an ethylene-unprimed plant (left) with an ethylene-primed one (right), both of the same age, from the Binder lab at the University of Tennessee, Knoxville.

We investigated whether various plant species responded similarly to ethylene exposure during seed germination. Our tests included tomato, cucumber, wheat, and arugula seeds, all of which exhibited enhanced growth.

Remarkably, the brief ethylene exposure also heightened their tolerance to stressors like salt, high temperatures, and low oxygen.

Priming effects refer to long-term growth and stress tolerance enhancements following brief stimulus exposure. This concept, akin to priming a pump for easier and quicker activation, has been explored in various plant growth stages. Seed priming with chemicals and stresses is widely studied for its simplicity and potential agricultural applicability.

Exploring the Mechanisms

Post-experiment, our lab has been deciphering the mechanisms enabling these ethylene-exposed plants to exhibit greater growth and stress tolerance. One hypothesis is that ethylene priming boosts photosynthesis, where plants convert light into sugars.

Our findings indicate a significant rise in carbon fixation, implying a heightened CO₂ intake from the atmosphere.

Corresponding with increased photosynthesis is a surge in plant carbohydrate levels. This includes starch (a plant energy storage molecule) and sugars like sucrose and glucose, crucial for immediate energy. These higher molecule concentrations are linked to amplified growth and improved stress endurance.

Our research suggests that environmental conditions during germination can profoundly and enduringly affect plants, potentially enhancing both their size and stress resilience. Understanding these mechanisms is increasingly vital, with implications for enhancing global crop yields.

Authored by Brad Binder, Professor of Biochemistry & Cellular and Molecular Biology, University of Tennessee.

This article is adapted from an original publication in The Conversation.

Frequently Asked Questions (FAQs) about Ethylene Priming in Plants

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