Amenizando os efeitos do déficit hídrico em cana-de-açúcar com a nutrição nitrogenada

Author(s)

Maria Dolores Pissolato

• Document type: Master's Dissertation
• Press: Campinas, SP.
• Institution: Universidade Estadual de Campinas (UNICAMP). Instituto de Biologia
• Defense date: 2019-08-29

Examining board members

Rafael Vasconcelos Ribeiro; Eduardo Caruso Machado; Sara Adrián López de Andrade

• Advisor: Rafael Vasconcelos Ribeiro

Abstract

Water and nitrogen (N) are two of the most limiting factors in world agricultural production, both strongly associated with the photosynthetic CO2 assimilation. Modifications in the metabolism of N under water deficit conditions are less studied in C4 plants and the information available is still fragmented. It is known that the radical nitric oxide (NO) is an important signaling molecule in several biological systems, and has a protective role acting mainly against free radicals formed under oxidative stress. Although the mechanisms of NO synthesis and its regulation are complex and poorly understood, nitrate reductase (NR) is a key enzyme for the assimilation of nitrogen in plants and has been proposed as an important enzymatic pathway for NO production through nitrite reduction. Then, the objective of this work was to evaluate the influence of nitrogen nutrition on the physiological responses of sugarcane plants to water deficit, considering the photosynthetic activity, antioxidant metabolism and plant growth. The hypothesis to be tested is that plants receiving more nitrate as source of N will have a higher activity of NR and will produce more NO under water deficit when compared to plants supplied with less nitrate. We expected that NO alleviates the effects of water deficit in sugarcane plants, reducing oxidative damage and improving photosynthesis and plant growth under low water availability. Sugarcane plants were grown in nutrient solution containing the same N concentration, however, varying the proportions of nitrate:ammonium in 100:0 and 70:30. These proportions were defined in a previous experiment, in which we evaluated the responses of sugarcane to the variation of the nitrate:ammonium ratio. We found that plants can be supplied with up to 30% of ammonium without impairment of photosynthesis and growth. Water deficit was induced after adding PEG-8000 to the nutrient solution (reducing the osmotic potential from -0.15 to -0.75 MPa). Plants under water deficit and supplied with more nitrate (100:0) showed a higher root accumulation of nitrate and nitrite, as well as higher root NR activity when compared to plants supplied with less nitrate (70:30). In addition, plants supplied with only nitrate showed higher NO production in roots, higher photosynthetic rates and stomatal conductance, resulting in higher biomass. The lower accumulation of reactive oxygen species (ROS) found in plants under water deficit supplied 100:0 solution was associated with increased activity of catalase in leaves and superoxide dismutase and ascorbate peroxidase in roots. As conclusion, plants supplied with more nitrate presented higher NR activity and produced more NO, reducing the oxidative damage caused by water deficit and consequently favoring photosynthetic metabolism under low water availability. The results of this study also revealed that the NO synthesis is associated with increased NR activity, being an important metabolic pathway in sugarcane plants (AU)

• FAPESP's process: 17/11279-7 - Alleviating the impact of water deficit on sugarcane photosynthesis by managing nitrogen source
• Grantee: Maria Dolores Pissolato
• Support Opportunities: Scholarships in Brazil - Master