دانلود رایگان مقاله انگلیسی سمیت کروم (VI) در گیاهان حبوبات: اثرات مدولاسیون Rhizobial Symbiosis - هینداوی 2018

Most legume species have the ability to establish a symbiotic relationship with soil nitrogen-fixing rhizobacteria that promote plant growth and productivity. There is an increasing evidence of reactive oxygen species (ROS) important role in formation of legume-rhizobium symbiosis and nodule functioning. Environmental pollutants such as chromium compounds can cause damage to rhizobia, legumes, and their symbiosis. In plants, toxic effects of chromium(VI) compounds are associated with the increased production of ROS and oxidative stress development as well as with inhibition of pigment synthesis and modification of virtually all cellular components. These metabolic changes result in inhibition of seed germination and seedling development as well as reduction of plant biomass and crop yield. However, if plants establish symbiosis with rhizobia, heavy metals are accumulated preferentially in nodules decreasing the toxicity of metals to the host plant. This review summarizes data on toxic effects of chromium on legume plants and legume-rhizobium symbiosis. In addition, we discussed the role of oxidative stress in both chromium toxicity and formation of rhizobial symbiosis and use of nodule bacteria for minimizing toxic effects of chromium on plants.

6. Conclusions and Perspectives

The presence of chromium compounds in soils inhibits seed germination and induces various morphological and physiological defects in many plants, including legumes. Toxicity of chromium in plants is connected with the enhanced ROS formation and oxidative stress development resulting in the intensified protein modification, lipid peroxidation, and DNA damage. In legume-rhizobial symbiosis both host plant and nodule bacteria undergo oxidative stress induced by chromium, with rhizobia being more stressed due to preferential Cr accumulation in root nodules. Available data suggest that inoculation with nodule bacteria can be considered as an effective approach to minimize toxic effects of chromium and other heavy metals on agricultural plants. At the same time, the protective efficacy of nodule bacteria depends on many factors such as type and concentrations of metals, compatibility of partners, virulence, adaptive capacity, and nitrogen-fixing activity of bacteria. Therefore, the effects of heavy metal on legume-rhizobium symbiosis and search of ways to enhance metal resistance of nodule bacteria are perspective potential research direction. It seems that Cr at low concentrations may induce mild oxidative stress [128], which can have beneficial rather than detrimental effects on legume-rhizobium symbiosis and plant metabolic processes (Figure 2). As known, mild oxidative stress may induce adaptive response, which enhances resistance to many lethal stresses [128]. In addition, mild oxidative stress plays an important role in establishment of effective legumerhizobium symbiosis [103]. We propose that using the pretreatment with nodule bacteria at low levels of oxidants can aid bacteria to resist high levels of heavy metals in the environment. The construction of nodule bacterial strains with higher resistance to environmental stresses may be a great opportunity to increase the benefit from their use in bioremediation and cultivation at polluted areas.