Strategically dosing seeds with ethylene—a growth hormone often used to artificially ripen fruit—boosts their size, strength, and resilience to stress, finds a study that could help safeguard future crops against climate change.
Farmers are on a constant mission to boost the growth and yield of their crops. But in one of nature’s trade-offs, higher-yielding plants tend to be less resistant to stress. To get around this impasse, researchers have experimented with the highly promising ethylene, which plays a dual regulatory role in both plant growth and stress responses.
But despite its known benefits, when previous researchers have applied ethylene artificially to seeds in the past, the dosing protocol has resulted in warped and stunted plants—quite the opposite of what ethylene accomplishes naturally. Most of these studies have applied ethylene continuously to the seeds, and under light conditions, explains Brad Binder, professor of biochemistry & cellular and molecular biology at the University of Tennessee Knoxville, and corresponding author on the new PNAS Nexus research.
In the new study, Binder and his team sought to fine tune this process, and it seems they’ve identified a sweet spot: by dosing seeds with ethylene in conditions of darkness, but then crucially tapering it off when the seedlings were exposed to light.
This more tailored approach made a remarkable difference. In fact, in experiments where the researchers pre-treated seeds of Arabidopsis (thale cress), tomato, cucumber, and wheat, and then exposed the seedlings to light while tapering off ethylene, plants grew to have more abundant and lengthier roots, as well as being weightier and taller overall. In particular, tomato plants went on to grow taller and produce more leaves; cucumber seedling leaves grew much faster; and wheat seedlings showed more rapid root growth than controls.
“We think that ethylene is doing something to the seedlings in darkness that then leads to changes that enhance plant growth and stress tolerance. We’re not yet sure what this “something” is but this is the focus of our research now,” Binder says.
Detailed investigations into thale cress plant tissue also revealed that the levels of glucose, sucrose, and starch shot up by 266%, 446%, and 87% respectively, pointing to greater productivity from photosynthesis. In fact, analyses into the genes and metabolic processes of these plants showed an uptick in processes linked to cell division and photosynthesis, after the ethylene was applied.
And what’s more, this accelerated growth didn’t seem to undercut the plants’ ability to cope with stress. When the researchers blasted seedlings with high temperatures of 43°C, increased the salt levels in the soil, and deprived them of oxygen, the pre-treated thale cress were more likely to survive these harsh conditions than the untreated controls. Notably, almost 100% of the treated seedlings survived the exposure to salinity and high temperatures in particular, whereas untreated plants became bleached and soon died.
The findings suggest that dosing plants with ethylene primes them for healthier growth, with effects that last long after they emerge from the soil. The key appears to be the transient and limited the application—a case of less is more.
The researchers think their findings hold potential to manipulate crop growth especially in specific growing conditions where exposure to light can be controlled to maximize ethylene’s benefits. “In greenhouse applications it might be viable,” Binder says. “For instance, one could treat germinating plants, such as perhaps tomatoes, in darkness while they germinate, and then grow them in normal conditions. This would result in bigger and more stress tolerant plants,” he says.
Next up is to investigate how ethylene treatment affects the size and abundance of produce yielded by fruiting crops.
Brenya et. al. “Ethylene-mediated metabolic priming increases photosynthesis and metabolism to enhance plant growth and stress tolerance.” PNAS Nexus. 2023.
Image: Courtesy of Brad Binder