Discover the defense mechanism of plants to overcome adverse situations such as pests or droughts

Researchers at the University of Córdoba (UCO) have managed to determine the function of an enzyme in the regulation of nitric oxide, a component used by plants to stop adverse situations such as pests or droughts.

In a situation of biotic stress, such as insect infestation, or abiotic stress, such as exposure to metals or high temperatures, plants are able to trigger defense mechanisms to prevent damage from spreading. One of the main weapons used in these processes is nitric oxide. This molecule is a toxic compound that acts as a signal for the plant and induces a situation that can lead in certain cases to a programmed cell death to stop the advance of damage and save the rest of the organism. How the plant manages this nitric oxide continues to be an enigma for the scientific community. However, biochemists from the University of Córdoba and the Campus of International Excellence ceiA3 have managed to connect a piece of this molecular puzzle.

A family of proteins present in all forms of life plays a fundamental role in the metabolism of nitric oxide. These proteins are the hemoglobins, which, for example, animals with circulatory system allows them to transfer oxygen through the blood. However, the relationship of these proteins with nitric oxide seems even more ancestral than their relationship with oxygen. Likewise, nitric oxide is also present in the physiological regulation of all living beings. It plays a crucial role in the growth, development and defense of the organisms that carry out photosynthesis although in excess it is toxic for plants.

The UCO researchers analyzed the role of a specific type of hemoglobin in the regulation of nitric oxide. "We still do not know exactly how these hemoglobins work in plants, but we know that they serve to regulate nitric oxide and avoid toxic effects in these organisms", Explains Emilio Fernández Reyes, head of the research group Molecular biology of the assimilation of nitrate in algae at the University of Córdoba. "However, it is not known how plants synthesize nitric oxide and this information may be important to know the physiology of vegetables".

Together with Fernández, they have worked in the research team Emanuel Sanz Luque, Francisco Ocaña, Amaury de Montiagu, Alejandro Chamizo, Angel Llamas, Aurora Galán.

The research work has allowed to observe how hemoglobin reduces nitric oxide and with oxygen transforms this toxic compound into nitrate, which can assimilate the plant. For this, the scientists used a green alga, Chlamydomonas reinhardtii, which contains an unusual number of this type of hemoglobins, called truncated hemoglobins. The results have been recently published in the scientific journal The Plant Journal.

The researchers observed that one of these twelve truncated hemoglobins that the algae has, called THB1, was able to convert nitric oxide into nitrate efficiently in significant quantities. For this, he needed a protein called nitrate reductase, a central enzyme in the assimilation of nitrate. This protein is able to stop its main activity in the reduction of nitrate to yield electrons to the hemoglobin allowing this oxygen and nitric oxide to form nitrate. The interaction of these two proteins was evident when observing the surface charges of both enzymes. "When generating the images of the electrostatic potentials of both, we observed that they fit like two pieces of a puzzle", Explains the principal investigator.

The description of this molecular mechanism is a work of basic science. "Our function is to know how things happen, others will come to look for the applicability to the generated knowledge", Explains Fernández Reyes. In this case, the research can be used for different branches of knowledge such as Biology or Agronomic Engineering.



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