As sessile living things, plants must adapt and respond to their ever-changing environments. And in recent years, understanding how roots may regulate high temperatures has gained traction among scientists.

Biologists thought young plant shoots controlled temperature within the plants and acted as a transmitter that signaled the root to alter its growth, said Marcel Quint, a plant biologist and study author at the Martin Luther University Halle-Wittenberg, in a statement.

Now, plant biologists found that roots can also measure heat without help from the plant’s shoots to help regulate temperatures, in a recent study published in The EMBO Journal. The find gives researchers insight into creating more drought-resistant plants on a warming planet.

Heat Stress and Plant Growth

Previously, researchers have investigated how plants respond to temperature using various coping strategies. One growth adaption that promotes plant organ growth as a response to high temperatures is called thermomorphogenesis. The method helps plants cool down by dissipating heat.

While plants can acclimate to warmer temperatures, higher ambient temperatures can still cause negative effects on plant growth and development. When under severe heat stress, plants can lose their leaves, buds and flowers, as lower leaf counts reduce water loss through stomates, stems and other parts of the plant.

To monitor plant growth in the recent study, the team used climate chambers to simulate rising ambient temperatures. Researchers rose temperatures from 60 to 82.4 degrees Fahrenheit and used three different types of plants, the thale cress (Arabidopsis thaliana), vegetable cabbage (Brassica oleracea) and the tomato plant (Solanum lycop).

For one of the experiments, the team cut off the plant shoots but still allowed the roots to grow. “We found that the roots were not affected by this and grew at elevated temperatures in the same way as on plants with intact shoots. The higher temperature stimulated cell division, and the roots became significantly longer,” said Quint.

The team found that in plants with modified shoots that would not react to heat, the roots still sensed and reacted to heat stimuli. When temperatures rise, scientists suspect that plants will respond to it by promoting more root growth so that the roots can reach deeper regions in the soil with more water. Having the roots react to varying temperatures confirmed that the roots sense heat on their own, without help from other parts of the plant. 

Plant Hormones

For plants, roots are a vital organ. They absorb water, nutrients, respond to their environments, and can sense light to adapt and grow successfully. Plants control their root length and root direction, and development using hormones called auxins, and cytokinins, to name a few.

During the experiments, the team found an increase in auxin, a plant growth hormone, in the roots. Once the auxin reached the roots, it stimulated cell division and allowed the roots to dig deeper into the soils to cool off.

“As heat and drought usually occur in tandem, it makes sense for the plants to tap into deeper and cooler soil layers that contain water,” Quint said.

Plant shoots react to heat similarly to roots. When shoots detect heat, the cells also produce more auxin to signal the plant’s stalk to grow taller and have its leaves grow smaller and farther apart, and some plants may even change color. By understanding how plants react to heat stress, researchers may unlock the key to drought-resistant crops in light of climate change.

“In view of climate change, root growth is becoming more and more important for breeding. Understanding the molecular basis for temperature-dependent root growth might help to effectively equip plants against drought stress and achieve stable yields in the long term,” said Quint. Quint’s team plans to continue observing changes in root behavior in the coming years.

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