Exposing plants to unusual chemicals early may boost their growth and help feed the world

Exposing plants to unusual chemicals early may boost their growth and help feed the world

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The plant on the left is not equipped with ethylene, while the plant on the right is equipped with ethylene. Both plants are the same age. Source: Bender Laboratory, University of Tennessee, Knoxville

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The plant on the left is not equipped with ethylene, while the plant on the right is equipped with ethylene. Both plants are the same age. Source: Bender Laboratory, University of Tennessee, Knoxville

Like any other living organism, plants can experience stress. Conditions such as heat and drought are usually what lead to this stress, and when stressed, plants may not grow as much or produce as much. This can be a problem for farmers, so many scientists have tried to genetically modify plants to be more resilient.

But plants modified to produce higher yields tend to be less stress-tolerant because they put more energy into growth than into protecting against stress. Likewise, improving plants’ ability to withstand stress often results in fewer plants because they expend more energy protecting than growing. This conundrum makes it difficult to improve crop production.

I have been studying how the plant hormone ethylene regulates growth and stress responses in plants. In a study published in July 2023, my lab made an interesting and unexpected observation. We have found that when seeds germinate in the dark, as they normally do underground, adding ethylene can increase their growth and stress tolerance.

Ethylene is a plant hormone

Plants cannot move, so they cannot avoid stressful environmental conditions such as heat and drought. They receive a variety of signals from their environment such as light and temperature that shape how they grow, develop and cope with stressful conditions. As part of this regulation, plants produce various hormones that are part of a regulatory network that allows them to adapt to environmental conditions.

Ethylene was first discovered as a gaseous plant hormone more than 100 years ago. Since then, research has shown that all land plants studied produce ethylene. In addition to controlling growth and responding to stress, it is also involved in other processes such as causing leaves to change color in autumn and stimulating fruit ripening.

Ethylene as a means of processing plants

My lab focuses on how plants and bacteria sense ethylene and how it interacts with other hormone pathways to regulate plant growth. While conducting this research, my group made an accidental discovery.

We were doing an experiment where we had seeds germinate in a dark room. Seed germination is a critical period in a plant’s life, when, under favorable conditions, a seed transforms from a dormant state into a seedling.

In this experiment, we exposed seeds to ethylene gas for several days to see what effect this might have. Then we removed the ethylene. Usually, this is where the experience ends. But after collecting data on these seedlings, we transferred them to a light vehicle. This isn’t something we normally do, but we wanted to grow the plants to adulthood so we could have seeds for future experiments.

During photosynthesis and carbon fixation, plants absorb sunlight and convert it into sugars that they use to grow.

After several days of holding the seedlings under the light, some members of the laboratory made an unexpected and startling observation that the plants that had been briefly heated with the gas were much larger. They had larger leaves as well as longer and more complex root systems than plants that were not exposed to ethylene. These plants continued to grow at a faster rate throughout their lives.

My colleagues and I wanted to know whether various plant species showed growth stimulation when exposed to ethylene during seed germination. We found that the answer is yes. We tested the effects of short-term ethylene treatment on the germination of tomato, cucumber, wheat, and arugula seeds, all of which grew larger.

But what made this observation unusual and exciting is that the short ethylene treatment also increased tolerance to various stresses such as salt stress, high temperature and low oxygen conditions.

The long-term effects on growth and stress tolerance resulting from short exposure to a stimulus are often called primary effects. You can think of this like priming the pump, as priming helps start the pump easier and faster. Studies have investigated how plants grow after conditioning at different ages and stages of development. But seed priming with different chemicals and stresses has probably been the most studied because it is easy to implement and, if successful, can be used by farmers.

How it works?

Since that first experiment, my team in the lab has been trying to figure out the mechanisms that allow these ethylene-exposed plants to grow larger and withstand more stress. We’ve found some possible explanations.

The first is that ethylene preparation increases photosynthesis, the processes plants use to produce sugars from light. Part of the photosynthesis process involves what’s called carbon fixation, where plants take in carbon dioxide2 of the atmosphere and use of carbon dioxide2 Molecules as the building blocks for making sugars.

My team showed in the lab that there is a significant increase in carbon fixation, which means that plants receive a much larger amount of carbon dioxide2 From the atmosphere.

The increase in photosynthesis is associated with a significant increase in carbohydrate levels throughout the plant. This includes significant increases in starch, an energy storage molecule in plants, and two sugars, sucrose and glucose, which provide quick energy to plants.

More of these molecules in the plant has been linked to increased growth and a better ability of plants to withstand stressful conditions.

Our study shows that environmental conditions during germination can have profound and long-lasting effects on plants that can simultaneously increase their size and stress tolerance. Understanding the mechanisms of this is more important than ever and could help improve crop production to feed the world’s population.

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