Cerium as alleviator of drought-induced stress in Phaseolus vulgaris

Abstract

The Rare Earth Elements (REE), according to the International Union of Pure and Applied Chemistry (IUPAC), are a group composed of 17 chemical elements. Except for prometium (Pm), which does not occurs naturally on the environment, all REE occur in abundance on Earth’s surface and their presence has been related to almost all rocks formation. Among them, cerium (Ce) is the most abundant REE. Besides its large use to the modern world, REE have also been utilized on agriculture. China, the principal holder of REE reserves worldwide, keeps active the application of formulated products containing REE since the 70’s. In this country, the continuous use of the formulated products relies on the gain of crop productivity and quality, mentioned to benefit around 50 crops. The favorable results have stimulated the interest of scientific researchers to figure out the mode of action of these elements on plants, because, at the present moment, their essentiality has not been proved yet. In addition, there are many inconsistences regarding the reported yield gains. However, the state of art clearly shows that Ce and other REE may act directly on many plant physiology processes. For example, Ce may act on the regulation of antioxidant systems, on the cell membrane functionality, and on the production of beneficial compounds, such as proline. Proline plays an important role in plants, acting as a molecule with antioxidant, chelator, and signaling properties. The improvement of plant physiology suggests that Ce might alleviate abiotic stresses; therefore, it might be a beneficial effect of this element on plants. Nevertheless, the essentiality of the interaction Ce-plant remains unknown and, it is still limited the knowledge about the mechanisms of Ce as an alleviator of stresses. For this reason, the aim of this study was to evaluate the effects of Ce on growth and development of Phaseolus vulgaris under water stress and also promote a better understanding of the role of this REE on plant physiology through the analysis of some biochemical characteristics and proline content. To achieve this, a greenhouse experiment was conducted to evaluate the effect of six Ce 3+ concentrations (0, 0.1, 0.9, 8.1, and 72.9 µM) on the development and physiological traits of Phaseolus vulgaris grown in nutrient solution under normal condition (osmotic potential of -0.1 MPa) or under induced drought stress (osmotic potential of -0.3 MPa) caused by the addition of polyethylene glycol to the nutrient solution. The results showed that Ce 3+ beneficial effects were more pronounced under drought stress. Under induced water stress, Ce 3+ treated plants displayed significant increments on growth and development compared to control plants. Furthermore, plants treated with low Ce 3+ concentrations displayed mean values significantly higher compared to control for plant parameters related to gas exchange levels. The findings suggest that Ce 3+ might be able to alleviate drought effects. Additional relevant effects promoted by Ce 3+ on plants were reductions on leaf contents of malondialdehyde (MDA), hydrogen peroxide (H2O2), and proline, a stress indicator in plants. Therefore, this study may help us better understand the positive effects often related to this important REE (Ce) on the scientific literature.