Adubação molíbdica e bactérias promotoras de crescimento na nutrição nitrogenada da cana-de-açúcar

Abstract

Molybdenum (Mo) is an anionic micronutrient that plays a key role in enzymes such as nitrate reductase and nitrogenase responsible for the assimilation of NO3 and biological nitrogen fixation (FBN), respectively. Nitrate reductase acts in the first step of reducing N-nitric and is fundamental in the assimilation of nitrogen. In another perspective, FBN performed by diazotrophic bacteria is considered the main natural way of entering N in agricultural systems and for this reason it is considered as a sustainable alternative to nitrogen fertilizers. However, the contributions obtained by inoculating bacteria are small and uncertain, and therefore, the mechanisms for promoting plant growth carried out by bacteria (BPCP) have been investigated in order to clarify and understand which ones are most active in the process. For this type of investigation, the analysis of proteins can guide the knowledge of these mechanisms, since they are directly linked to the formation of physiological characteristics that regulate phenotypes to adapt to certain changes. In view of the context, two studies were carried out: the first to evaluate the contribution of BPCP in conjunction with Mo fertilizer and associated with N in FBN in nitrogen nutrition and in the development of sugarcane and the second to identify the set of proteins that are potentially accumulated in response to the application of Mo, inoculation and N in sugarcane. In the first study, two cultivation cycles were carried out and plant growth parameters, activity of the nitrate reductase enzyme, FBN, nutrient contents and accumulations were evaluated. In the second study, plants with higher shoot biomass in the first study were subjected to extraction of total soluble proteins from leaf +1 and comparisons were made in four SDS-PAGE electrophoretic profiles for application or not of molybdic fertilizer when associated with inoculation of the inoculant ST, GHABH when combined or not with nitrogen fertilization. Our results showed that the micronutrient associated with the ST inoculant was more active in the process of N assimilation via NO3- while in association with the GHABH inoculant it was more active in the FBN. However, the increase via FBN source was not sufficient to supply the crop's demand, since the fertilizer source contributed with most of the nitrogen nutrition. In this perspective, the ST bacterium associated with Mo showed the best results acting as a biostimulant and has potential for use as a new technological package associated with intermediate N doses, since they stimulate the best growth and development of the plant and the best use of the available N more efficient. Comparative proteomics found 46 sets of differential proteins, but only 28 were identified (60.86%). Inoculation acts mainly on the accumulation of proteins related to N absorption and metabolism, while the inoculation of BPCP associated with Mo acts on the accumulation of differential proteins related to sulfur metabolism, photosynthesis and hormonal mechanisms, especially with regard to auxins, abscisic acid and ethylene in the cultivation of sugarcane. Our research is based on an efficient and sustainable fertility management by applying a viable and economical input. These results not only deepen our understanding of the influence of Mo on the sugarcane proteome, but also provide new information on the molecular mechanism of culture regulated by Mo and by BPCP. Thus, this research is innovative, and makes it possible, in the short term, to identify sustainable alternatives, with reduced cost for sugarcane.