Expressão gênica de transportadores de nitrato e amônio, proteínas reguladoras NAR e bombas de prótons em arroz (Oryza sativa L.) e seus efeitos na eficiência de absorção de nitrogênio

Abstract

The main goal of this study was to evaluate the nitrogen usage efficiency (NUE) of plants for a low input agriculture, as a fundamental step for tropical agriculture development. The objective was to evaluate the effect of N deficiency and resupply on expression of ten PM H+- ATPase isoforms, and NO3 - and NH4 + transporters in rice. Two experiments were set, one with the Nipponbare variety, to evaluate expression of PM H+-ATPase; and the other with IAC47 (improved) and Piaui (traditional) varieties, to study how PM H+-ATPase and NO3 - transporters behaved in varieties with contrasting N-use efficiency. The NO3 - and NH4 + uptake were highest under N-resupply. The NO3 --N resupply after 3 days of N-deficiency resulted in induction of OsA1, OsA2, OsA5 and OsA7 PM-H+-ATPases in the shoot, and of OsA2, OsA5, OsA7 and OsA8 in the roots. NH4 +-N resupply resulted in induction of the OsA1, OsA3, and OsA7 isoforms in roots and OsA1 in the shoots. A correlation was observed between nitrate and ammonium uptake, and an increase in the PM H+-ATPases. In the roots, the NO3 - transporters OsNRT2.1 and OsNRT2.2 had higher induction under NO3 - resupply, while the NH4 + transporter OsAMT1.1 and OsAMT1.2 were induced by NH4 +-N starvation. These results showed that the expression of PM H+-ATPases isoforms is related to both NO3 - and NH4 + transporters and in which plant part it takes place. The knowledge of the interaction between N-transporters and PM H+-ATPases specific isoforms is important for understanding NUE in plants. Two H+-ATPases isofoms OsA2 e OsA7 that were most induced under Nressuply can be thought as the most probable genes to affect N-uptake efficiency in rice. The second experiment showed that the varieties IAC-47 and Piaui differ widely about the N usage. The Piaui variety showed the highest level of nitrate and free Amino-N, and the lowest levels of NH4 +. Also, this variety had the highest PM H+-ATPase activity 24 hs after resupply with 0.2 mM NO3 --N, as well as the highest expression of the PM H+-ATPase OsA2 and OsA7. The Piaui variety showed the highest nitrate influx under N-resupply (0.2 and 5.0 mM NO3 --N) as well as higher expression of OsNRT2.1, OsNRT2.2 and OsNAR2.1 under those treatments. These results suggest that the highest NO3 - uptake of Piaui variety under Nresupply may be related to the highest expression of genes that code for nitrate transporters and PM H+-ATPases.