Roots are capable of measuring heat on their own, new study shows

Newswise — Plant roots possess their own thermometer to gauge the soil temperature in their vicinity and adapt their growth accordingly. By conducting extensive trials, a group headed by Martin Luther University Halle-Wittenberg (MLU) has successfully illustrated the existence of a distinct temperature detection and response mechanism within roots. In a fresh investigation featured in The EMBO Journal, the researchers additionally offer a novel account of how roots autonomously perceive and respond to elevated temperatures. These findings hold the potential to facilitate the development of innovative methodologies for plant breeding.

Using climate chambers, the researchers conducted investigations on the response of the model plant organism thale cress, as well as two crops, cabbage and tomatoes, to escalating ambient temperatures. They raised the ambient temperature from 20 to 28°C (68 to 82.4 degrees Fahrenheit). "Previously, it was believed that the plant shoot governed the entire process and served as a long-distance transmitter that communicated to the roots, instructing them to adjust their growth," explains Professor Marcel Quint from the Institute of Agricultural and Nutritional Sciences at MLU. Through extensive collaborative experiments with researchers from the Leibniz Institute of Plant Biochemistry (IPB), ETH Zurich, and the Max Planck Institute for Plant Breeding Research in Cologne, Quint's team has now successfully refuted this assumption. In one experiment, the scientists severed the shoots of the plants while allowing the roots to continue growing. "We discovered that the roots remained unaffected and continued growing at higher temperatures, just as they did in plants with intact shoots. The elevated temperature prompted cell division and led to significantly longer roots," Quint explains. The team also utilized mutant plants whose shoots were no longer capable of detecting and responding to higher temperatures. These plants were then grafted onto roots without this defect. Even in this scenario, the roots demonstrated the ability to respond to soil heat, despite the inactivity of the shoot.

In all of their conducted experiments, the researchers observed a consistent trend: root cells exhibited an elevated production of the growth hormone auxin, which was subsequently transported to the tips of the roots. At this location, auxin stimulated cell division, facilitating the roots' ability to extend deeper into the soil. "Given that heat and drought often coincide, it is logical for plants to exploit deeper soil layers that offer cooler temperatures and a water source," elucidates Quint.

For quite some time, scientists have possessed an understanding of how plant shoots respond to elevated temperatures. In this scenario, the cells within the shoot display an increased production of auxin, similar to the roots. However, the plant's response differs between shoots and roots. In the shoot, the cells elongate, causing the stem to grow taller, while the leaves become narrower and are spaced farther apart.

The study's findings also offer valuable insights for the field of plant breeding. Given the context of climate change, the significance of root growth in breeding is increasingly recognized. Quint highlights the importance of comprehending the molecular mechanisms underlying temperature-dependent root growth, as it can aid in equipping plants to better withstand drought stress and achieve long-term stable yields. Quint and his team plan to further pursue research in this area in the years to come. Notably, they recently received a research grant of approximately 500,000 euros from the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) for a new project focusing on precisely this topic.

The study was funded by the DFG, the Chinese Scholarship Fund, the Rosa Luxemburg Foundation, the Alexander von Humboldt Foundation and the Max Planck Society.

Study: Ai H. et al. Auxin-dependent regulation of cell division rates governs root thermomorphogenesis. The EMBO Journal (2023): doi: 10.15252/embj.2022111926