Growing in the shade: a finding that could help improve agricultural performance

Scientists have gained key knowledge about plants that has the potential to help improve the performance of agricultural crops.

In agricultural fields with high crop densities, plants inevitably shade each other. Since they cannot move to look for better conditions, what they do is modify the shape of their bodies and the growth of the different organs, so that they can adjust to the situation. Knowing the mechanisms underlying these changes well enough is essential to develop strategies that, in the future, will improve agricultural performance.

With this goal, an international team led by Argentine researchers María José Iglesias and Jorge Casal has discovered an unexpected internal regulation mechanism in plants, which has allowed these scientists to obtain complete knowledge about the response pathway used by plants. plants to face the shade.

In living organisms, various processes generate groups of oxidant molecules such as reactive oxygen species or ROS, which in turn are linked to other reactive species such as nitric oxide (NO). “Both molecules are produced from normal cellular metabolism, for example during photosynthesis, but under certain conditions at high concentrations they can have a negative effect, overoxidizing and damaging different cellular components such as proteins, lipids and DNA. We asked ourselves if the ROS/NO signals had any role in an environment with a lot of shade, in which the plant does or does produce less photosynthesis,” agronomist Jorge Casal, head of the Physiology Laboratory, explained to the CyTA-Leloir Agency. Molecular Studies of the Leloir Institute Foundation (FIL) and the Institute of Physiological and Ecological Research Linked to Agriculture (IFEVA), of the Faculty of Agronomy of the University of Buenos Aires Aires (UBA).

“Indeed,” continued Casal, “ROS/NO signals decrease in the foliage of plants exposed to shade, but we were surprised to see that the opposite happened in the stem: despite the shade, there were more ROS/NO signals.” ”. According to the CONICET researcher, this immediately led them to wonder how these increases are generated and if they serve any function.

To find the answers, the researchers used specimens of the plant Arabidopsis thaliana (a plant model that shares genetic mechanisms with wheat, corn and other relevant crops), in which they measured growth against different availability of ROS/NO, both by of pharmacological and genetic approaches.

Four of the members of the research team. From left to right: Martina Legris, Cecilia Costigliolo Rojas, María José Iglesias and Jorge Casal. (Photo: CyTA-Leloir Agency / UBA)

“Among other things, we used specimens genetically lacking enzymes that produce ROS towards the external environment of the cells (called the apoplast). We saw that, indeed, this signal is necessary for stem growth in response to shade, and that the COP1 protein plays a central role by being biochemically modified by these oxidative signals, changing its location towards the interior of the cell nucleus.” explained Iglesias, doctor in Biological Sciences, first author of the study and current head of the Laboratory of Redox Regulations in Plants of the Institute of Physiology, Molecular Biology and Neurosciences (IFIBYNE), which depends on the Faculty of Exact Sciences and Naturals of the UBA and CONICET. (When this study began, Iglesias was part of the laboratory directed by Casal at the FIL).

On the other hand, when plants grow as a crop in a field, the shade they receive is irregular because it can impact one part of the stem while the rays of sunlight arrive on the opposite side. “We thought, then, that ROS/NO could constitute mobile signals in the space between cells (apoplast), capable of carrying information from one cell to the other, allowing them to ‘communicate’ and coordinate,” said Casal. “Indeed,” he explained, “we observed that when plants were exposed to conflicting signals (simulating shadow on one side and light on the other), those that were genetically normal kept their stems very vertical. On the other hand, in those modified to not produce ROS or whose COP1 could not respond to ROS, the stems twisted with respect to the vertical because the cells on one side of the stem grow more than those on the opposite side. In other words, the generation of ROS/NO signals and their perception by COP1 are necessary for the different stem cells to grow in a coordinated manner.”

Until the publication of this work, it was not known that shade, specifically in stems, induces the production of ROS/NO signals in this way or how it induced them and, much less, that they could be part of an internal coordination mechanism for maintain plant growth even in that adverse situation.

“This process that we discovered may be important in crops, because when the stems bend, the wind and rain overturn them more easily, which makes it impossible to harvest the grains that, irremediably, are lost on the ground,” Casal concluded.

The study is titled “Shade-induced ROS/NO reinforce COP1-mediated diffuse cell growth.” And it has been published in the academic journal Proceedings of the National Academy of Sciences (PNAS). (Source: CyTA-Leloir Agency)