Morfologia, arquitetura radicular e metabolismo de nitrogênio em variedades de arroz sob baixa disponibilidade de amônio

Abstract

Root morphology is a major factor related to the efficiency of nutrient acquisition. For this reason, this work compared this characteristic in three contrasting rice varieties: IAC 47 (improved variety) and two traditional varieties cultivated in the state of Maranhão (Piauí and Manteiga originated in an environment with low nutrient input). These varieties were subjected to a low N-NH4+ supply and analyzed for the root morphology parameters, expression of ammonium high affinity transport system (OsAMT1.1~1.3) and GS activity in three segments of the root system. It was also determined the soluble fractions and total nitrogen in the different segments of the plants (leaves, sheaths and roots) to verify the metabolic alterations as a result of low ammonium input. The GS activity was higher in the second segment in the Manteiga and IAC-47 varieties compared to Piauí, in the other segments. A similar result was observed in the Manteiga variety in the third segment (bottom of the root system) submitted to NH4+ resupply. When grown without NH4+, the Manteiga variety showed higher OsAMT1.3 expression in the lower segment of the root system, and greater root growth, indicating a possible involvement of this transporter in the control of root morphology in rice plants. There was lower expression of OsAMT1.1 and OsAMT1.2 unlike OsAMT1.3 but being distributed to other segments of the root system. In resupply with NH4+ (38 DAG) there was repression of ammonium transporters in the bottom (PI) of the root system and increased expression of OsAMT1.2 the median part (PM) in Piauí variety. In the upper part of the roots (PS) higher levels of ammonium transporter expression was observed in the IAC-47, and Manteiga. This difference in expression between varieties originated from regions with low N availability (Piauí and Manteiga) and improved IAC-47 is an indication that under conditions of limited N, the highest expression of OsAMT1.3 may be associated with an increase in morphological parameters.