Knowing that roots integrate temperature information independent of shoots may help breeders develop better varieties
Plants respond to the ambient temperature with growth patterns that adjust as the temperature changes.
But how they do it has remained a mystery.
Recently, researchers at Martin Luther University in Halle-Wittenberg, Germany, discovered that roots’ temperature and sensing systems are independent of the plant’s shoots. The study could lead to new methods in plant breeding to further crops’ coping methods in the face of a warming world.
Professor Marcel Quint with the Institute of Agricultural and Nutritional Sciences at MLU said researchers wanted to understand the underlying mechanisms plants use to sense temperature changes and translate the changes into growth responses.
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He said the first 10 to 15 years of research in the field of study called thermomorphogenesis focused on understanding how shoots integrated temperature information, but researchers recently turned their attention to the roots.
The researchers worked with thale cress, cabbage and tomatoes and grew them in climate chambers to investigate their reactions to temperatures rising from 20 C to 28 C.
According to the news release, in one experiment scientists cut off the shoots of the plants but 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 (they would) on plants with intact shoots,” Quint said. “The higher temperature stimulated cell division and the roots became significantly longer.”
The researchers found the root cells increased production of the growth hormone auxin, which was transported to the root tips. Once there, the hormone stimulated cell division to enable the roots to reach deeper into the soil.
“Under natural conditions, high temperature often goes hand-in-hand with drought,” said Quint. “This makes the analysis more complicated because we need to vary more than one factor.”
He said the experiments are being carried out in many research groups around the world in attempts to further understand the responses.
He said shoots and roots respond differently to moderate changes in temperature.
“On the molecular level, shoot and root responses differ quite a bit. In roots, cell elongation is not so much affected by elevated temperature, but by an increase in cell division rates. If there is more cell division, then there are more cells in the root for it to grow longer. This is fundamentally different from the shoot: temperature-induced growth by cell division in the root vs. temperature-induced growth by cell elongation in the shoot.”
Under heat waves and heat stress, plants go into survival mode and the first thing they reduce is the application of resources for growth. In the root, the stem cell niches would degenerate, making cell division and therefore root growth impossible.
“Among crops there are ‘experts’ in this behaviour like sorghum and chickpea, which are very drought resistant because they can sit out such extreme conditions and return to growth afterwards without suffering too much damage,” said Quint. “Most crops would suffer more during these periods.”
Quint said he and other research groups working on root thermal dynamics are at the beginning of exploring this discipline. They still must identify root thermosensors.
“Knowing this might help to generate crops that are either more or less sensitive to temperature changes in the soil,” he said. “This will open opportunities to adapt a species’ temperature sensitivity in a meaningful way, depending on the environment they are usually grown in.”
Extreme weather events are becoming more frequent, turning the heads of crop breeders. Many were not initially interested in temperature signaling traits, arguing that they would automatically select for temperature resistant lines in their field trials.
“This notion has drastically changed,” said Quint. “With more accounts of extreme weather events, including heat waves during flowering or early flowering because of increased average ambient temperatures, breeders are now keen on heat sensitive traits.”
Quint said their next step is to see whether their observations hold up when doing trials in real soil systems.
“In view of climate change, root growth is becoming more and more important for breeding,” said Quint. “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. There are many approaches to better adapt root system architecture to challenging environmental conditions, but I am convinced that using temperature as a trigger to stimulate root growth may help to breed climate-resilient crops.”
The research was published in The EMBO Journal.
