Drought is a major limiting factor in crop yield, plants generally show a reduction in the rates of photosynthesis and growth, often associated with changes in plant metabolism. Nitric oxide (NO) has emerged as an important signaling molecule in various biological systems. It is postulated that NO plays a protective role by acting mainly on the interruption of free radicals formed under oxidative stress. Given the above, our objective is to evaluate the influence of NO in physiological responses of sugar cane (Saccharum spp) to drought stress. Additionally, we intend to determine the main sources of NO in genotypes with differential sensitivity to drought. Genotypes will be subjected to drought by adding PEG 8000 to the nutritive solution (osmotic potential of -0.75 MPa). In addition to evaluating the differential production of NO by plants limiting conditions, we also analyze the role of NO delivered through nutrient solutions of sodium nitroprusside (SNP). Evaluations will be divided into three experiments; the first will deal with the activity of enzymes synthesis, beyond the detection of NO in plants. The second will address the physiological analyzes such as gas exchange, photochemical activity, photosynthetic pigments, enzymes of photosynthetic metabolism and growth analysis in order to verify if NO is capable of attenuating growth inhibition and impairment of the electron transport chain in photosynthesis under stress conditions. The last experiment answer is NO potentiate antioxidant mechanisms, therefore, we will perform analyzes of reactive oxygen species and antioxidant enzyme system. The experiments are conducted in a randomized block design with five replicates and the data subjected to analysis of variance and the means were compared by Tukey test.
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