Acúmulo e remobilização de NO3- e eficiência de uso de nitrogênio em variedades tradicional e melhorada de arroz (Oryza sativa L.)

Abstract

The dynamics of accumulation and remobilization of NO3 -related protein content of the grains was studied in two varieties of rice, Piauí (traditional state of Maranhão) and IAC-47 (enhanced by research institutions). The experiment was conducted in a greenhouse of UFRuralRJ in the period August 2006 to February 2007, with a completely randomized design with a factorial arrangement 2x2x4, consisting of two varieties, two levels of NO3-, 0 and 150 kg N.ha-1, and four times of collection, to 35 days after transplanting (DAT), 15 and 30 days after anthesis (DAA) and a final collection of grain and dry, with three replications, with three replicates. Each collection, the plants were cut at ground level and separated in flag leaf, leaf 2, and lower leaf sheath + stem. In each segment the fractions were analyzed nitrogen (NO3 -, NH4+ and N-amino), soluble sugars, N-total and certain activities of nitrate Redutase, P-H+-ATPase, V-H+-ATPase, H+-PPase and Glutamine Sintetase. In grains, it was determined the weight of 1000 grains, number of full and hollow grains per pot, size (Length, width and thickness) and content of N-total, crude protein and protein fractions and the relationship glutelin/crude protein. The greater capacity of accumulation and remobilization of NO3-, under conditions of lower availability of nitrogen, was given the variety Piauí, by presenting a higher content of nitrate in detriment to growth, in the initial phase of growth and increased activity of VH+-ATPases found at the beginning of the reproductive period and a lower amount of nitrogen, in both the soluble form (NO3-), as structural (N-protein and others), at the end of the cycle, using the fastest way the N after anthesis, directing it to training and filling of grains. Although the content of crude protein and protein fractions not differ among varieties, on the lowest level of N, the traditional variety, showed higher productivity. Therefore, these results indicate greater efficiency in the use of N by the variety Piauí under conditions of low availability of this nutrient.