Arsenic (As) and cadmium (Cd) are very toxic and widespread environmental pollutants that endanger health to all the living organisms. They may enter into the food chain because they are easily absorbed by plant roots. These elements are able to induce deep changes in plants, often consisting in damages on their development, metabolism and productivity. The earliest and greatest damages occur in the root system, and cause inhibition of root growth and modifications of root architecture. Morphological, histological and developmental changes are frequently the plant response to abiotic stresses, and also occur after As and Cd exposure as result of very complex interactions among phytohormones, e.g., auxin and jasmonates, and stressors.
In this research the relation between jasmonates and auxin during the development of adventitious roots, and their lateral roots, under exposure to Cd and/or As will be investigated in rice seedlings, also using the cpm2 mutant blocked in jasmonic acid (JA) biosynthesis. To the aim, we will carry out morphological analysis on the root system of Nihonmasari (wt) and cpm2 mutant, exposed to Cd and/or As, in the presence or absence of exogenous methyl jasmonate (MeJA), the methyl ester of JA. Cadmium and As accumulation will be evaluated in the roots and shoots of the two genotypes exposed to As and/or Cd, as well as indole-3-acetic acid (IAA) and jasmonic acid (JA) endogenous levels. The expression levels of some jasmonate and auxin biosynthetic genes will be analyzed after treatment with the toxic elements. A histochemical analysis on OsDR5::GUS seedlings, exposed to As and/or Cd, combined or not with MeJA, will be carried out. Lastly, we will investigate the extent of lipid peroxidation, through the quantification of a decomposition product of polyunsaturated fatty acids, i.e. malondialdehyde (MDA), both in wt and cpm2 roots exposed to Cd and/or As.
Most plants, and in particular their root system, are seriously damaged when exposed to toxic metals. An alteration of the structure and organization of the root system prejudices the plant development and its productivity. This is particularly important for food species, such as Oryza sativa, because of the reduced productivity but also because the obtained product is not a safe food. Thus, studying the mechanisms at the base of the defence strategies of food species, in particular strategies activated in the root system, allows reaching important goals.
Environmental contamination due to As and Cd represents a serious worldwide risk for human health. These elements are classified in Group I carcinogenic to humans (IARC, 2012), and may cause acute or chronic toxicity. Severe pollution due to As affected numerous countries, among them Bangladesh, India, China and U.S.A. In Europe, it is paid attention to those countries with high As levels in soil and water, including Romania, Hungary and Italy. Frequently, in the above mentioned countries, As toxicity is strongly increased by Cd presence.
Rice is the staple food for the half of the world population, and, concerning Europe, Italy is the main rice producer and exporter. Rice is one of the most endangered cultures by As and Cd accumulation in grain. Although there is an urgent need to provide food security for the growing global population, enhancing rice productivity is very challenging especially under adverse environments. Despite in recent years many results have been achieved by studying the effects of toxic metals on rice, to date a comprehensive analysis of the effects of Cd and As on the root is still lacking. In particular, the interaction between auxin and jasmonate during root development and the possible protective role of jasmonate against lipid peroxidation and other damages caused by the pollutants are not yet investigated in this species.
The know-how and the skills of the participants to the Research Project and the availability of equipments and of rice transgenic and/or mutant lines are suitable to carry out the proposed program. Thus, the main innovations of the Research are related to the acquisition of knowledge on the mechanisms by which Oryza sativa can implement As and Cd tolerance, and to identification of practices that improve Cd and As accumulation in the root, reducing their translocation to aerial organs and mainly to the caryopsis that is used as food.