Scientists have solved the riddle of why plants grow taller when the ambient temperature is warmer.

The reason plants grow taller in response to warm temperatures is to maintain a proper carbon balance in their organs and not to avoid "heat stroke." At least, that is the hypothesis of a work published in the academic journal The New Phytologist that was carried out by Argentine scientists.

Until now, it was believed that the growth in height of plants was intended to get away from the extreme heat of the soil to protect sensitive tissues key to their development and also to expose them to greater air circulation in order to ensure greater ventilation and cooling .

Analyzing the global scale temperature and stem growth patterns, “our work discards this hypothesis. Plants grow taller in response to warm temperatures, not to avoid heat stroke, but to access more light and maintain an adequate balance between the carbon that the leaves fix and that they release, ”said Jorge Casal, a researcher at the Institute. of Physiological and Ecological Research Linked to Agriculture (IFEVA) and head of the Molecular Plant Physiology laboratory of the Leloir Institute Foundation (FIL).

The doctor in Biology and agronomist engineer stated that “if in a context of global warming we do not understand what the functions of the responses that plants display to temperature variations are, we will not be in a position to develop crops adaptable to climate change, a crucial objective to guarantee world food security ”.

Casal and his team carried out experiments in growth chambers and in the field with plants of different geographical origin of Arabidopsis, a plant model that shares genes with the main crops. Using populations of this species, they compared growth responses to warm temperatures and the presence of shading by neighboring plants. "Surprisingly, the populations that most responded to warm temperatures were those that also responded more strongly to shading," said Casal, senior researcher at CONICET and IFEVA, which depends on CONICET and the Faculty of Agronomy of the UBA.

Scientists know that the greatest growth of the stems in the shade has the function of reaching the light. The fact that responses to warm temperatures depend on genetic populations in a similar way to responses to shading suggests that they both serve the same purpose: to reach the light. Genomic and molecular analyzes reinforced the idea of ​​a shared genetic control for the response to both signals from the environment.

But why would growth responses to warm temperatures share with responses to shading the role of improving access to light? "We asked ourselves that question, and to investigate it we used instruments that measure the balance between the carbon dioxide that plants gain and that which they lose," Casal said.

In shady conditions there is little light for photosynthesis (a process that fixes carbon from the air). “If this is combined with high temperatures, what is the problem? The high temperature complicates the ability to photosynthesize and worse still, it accelerates the respiration that releases carbon ”, explained Casal.

And he continued: “In this scenario, to maintain appropriate levels of carbon, an appropriate balance between what it captures and releases, the plant grows, lengthening its stem to avoid the shade in order to access more light and thus increase its levels of photosynthesis. In this way it compensates for the loss of carbon that triggers a high respiration rate due to the increase in temperature ”.

"If we know why and for what a plant responds to certain stimuli, we will be in a position to develop a sustainable agriculture that is adaptable to climate change," said Casal. And he concluded: “If one starts from the erroneous premise that the growth in height of the plant exposed to warm temperatures is intended to prevent heat stroke, then it will be thought that taller crops should be developed. But if we know that the purpose of these responses is to maintain a balance in endogenous carbon levels, we will have to think about the development of crops where light penetrates better to guarantee adequate rates of photosynthesis ”.

The study also included Sofía Romero-Montepaone (first author) and Romina Sellaro, from IFEVA, Marcelo Yanovsky, Carlos Esteban Hernando, Cecilia Costigliolo-Rojas and Luciana Bianchimano, from FIL and CONICET, as well as Edmundo Ploschuk, from the Chair of Industrial Crops of the Faculty of Agronomy of the UBA. (Source: CyTA-Leloir Agency).