Avaliação através de RT-PCR da expressão dos genes que codificam para enzimas de assimilação de nitrogênio em variedades de arroz

Abstract

To verify the biochemical and physiological mechanisms involved in the nitrogen efficiency usage in rice, two rice varieties, Piauí (traditional from Maranhão State) and IAC 47 (breed), were cultivated in growth chambers, in hydroponics system, and submitted to different levels of N-NO3 -. As a study strategy the plants were cultivated for eighteen days, counted after germination, in a basic media, submitted for 72 hours without nitrogen, and them they were divided in three groups and applied the treatments. The first received 0.15 mM, a second group received 5 mM of N-NO3 - while a third group stayed without nitrogen. After treatment application, plants were harvested at 0, 1, 3, 6, 9, 24 and 48 hours, and samples of shoots and root were taken for determination of nitrate, ammonium-N, amino-N soluble sugars and gene expression of the enzymes nitrate redutase (NADH-NR) and glutamine synthetase isoforms (GS) (GS1.1, GS1.2, GS2, GS2c, GSI) at 0, 6 and 24 hours. The Piauí variety, after 72 hours without N, still kept small NO3 - levels. Also, the variety Piauí presented a higher expression of OsGS1.1 gene, which suggests the participation of this enzyme in the control of internal N fluxes, when in absence of nitrogen in the external solution. Under high N level, the Piauí variety accumulated larger amounts of amino-N in the leaves, had small nitrate redutase expression and activity. In spite of no differences in glutamine synthetase activity, an increase in OsGS2 (GS2) expression was observed, suggesting that this is the main GS isoform responsible for the GS activity in rice plants under nitrate nutrition.