Cadmium (Cd) and arsenic (As) contamination of soil and water causing toxicity/stress to food plants is an important constraint to crop productivity and quality. A plant exposed to toxic metals triggers a wide range of physiological and biochemical alterations and develops a series of strategies that allow to cope with the negative consequences of element toxicity. Roots are the first organs that encounter toxic metals. Thus roots must implement the strategies needed to reduce the negative effects of the toxic elements and possibly limit their transfer to edible organs.
Oryza sativa L. is one of the most cultivated food species, but it easy absorbs Cd and As. The latter causes dangerous effects on root development and plant growth and productivity. The correct distribution of auxin, due to a hormone polar transport and a local synthesis in the root meristem, is required for the genesis and maintenance of a functioning root system. The alterations in the synthesis/transport of auxin compromise root functionality. Cd and As accumulate in the root meristem and exert a negative action on the hormone homeostasis. Nitric oxide (NO) is involved in plant stress responses. It interacts with auxins during abiotic stress involving peroxisome activity. The role of peroxisomes in Cd/As induced responses, and, in particular, in the control of auxin metabolism in rice root, is poorly known. The thiols, particularly phytochelatins and their precursor GSH, bind As and Cd, resulting in toxicity alleviation. Furthermore, it is also known that metal-exposed plants show significant increases in the synthesis of secondary metabolites with antioxidant activity to protect the cells from the oxidative damages. The aims of the Proposal are to investigate the auxin-NO interaction during root formation in rice exposed to Cd/As, to analyze the variation of the thiol levels in the root and characterize the secondary metabolites involved, in relation to auxin and NO metabolism modifications.
The phytoremediation of soil polluted with metalloids and/or heavy metals represents an environmentally friendly and economically sustainable technology. However, to date, plants are poorly used for environmental remediation projects due to a limited number of naturally hyper-accumulator plants. 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, because of the reduced productivity, but also because the obtained product is not a safe food. Thus, to study the mechanisms at the base of the defence strategies of food species, in particular strategies activated in the root system, allows to reach important goals.
In fact, the Proposal could both increase basic knowledge about the extraordinary plasticity of the root system in response to environmental stimuli, and give useful information to application purposes. Useful application could result from the identification of key steps in the mechanisms/processes that increase plant capabilities to tolerate metal toxicity and/or in the mechanisms/processes that enhance root heavy metal/metalloid accumulation reducing their translocation to aerial organs.
Environmental Arsenic (As) and cadmium (Cd) contamination represents a serious worldwide risk for human health. As and Cd consumption, even though at low dosage, can cause cancer. These elements are classified in Group I ¿carcinogenic to humans¿ (IARC, 2004), and can cause acute or chronic toxicity. Toxic metals are present in the environment due to natural processes and anthropic activities. In particular, severe As pollution affected numerous countries, among them Bangladesh, India, China and U.S. 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 nitric oxide during root development and the possible involvement of the peroxisomes are not jet investigated, such as the variation of the thiol metabolism during this process. The know-how and the skills of the researchers involved in the Project and the available equipments 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 the rice can implement As and Cd tolerance and to identify practices that improve Cd and As accumulation in the root reducing its translocation to aerial organs and mainly in the grain.