Physiological and transcriptional characterization of the process of nitrate uptake and remobilization in sugarcane (Saccharum spp.)

Author(s)

Luís Henrique Damasceno Serezino

• Document type: Master's Dissertation
• Press: Piracicaba.
• Institution: Universidade de São Paulo (USP). Centro de Energia Nuclear na Agricultura (CENA/STB)
• Defense date: 2015-03-06

Examining board members

Antonio Vargas de Oliveira Figueira; Henrique Coutinho Junqueira Franco; Silvana Aparecida Creste Dias de Souza

• Advisor: Antonio Vargas de Oliveira Figueira

Abstract

The expansion of sugarcane (Saccharum spp.) cultivated area to marginal lands and the need to maintain high yield have led to increasing application of nitrogen fertilizers. However, this practice represents high economic and environmental costs. Compared to other crops, sugarcane displays a low response to N fertilization, but the causation of the low nitrogen use efficiency (NUE) remains unknown. To understand the mechanism involved in NUE, this study was carried out to conduct the physiological characterization of nitrate uptake and N remobilization in sugarcane by uptake kinetic analysis and translocation experiments using 15N. Further, the expression profile of genes encoding nitrate transporters (NRTs - NITRATE TRANSPORTERS) involved in both processes was determined. Plantlets of cultivar \'SP80-3280\' were exposed to various N supplement conditions to investigate the regulation of the uptake process. The lower efficiency in nitrate acquisition compared to ammonium was corroborated and extended for low N conditions. The occurrence in sugarcane roots of high affinity uptake systems (HATS, High Affinity Transport System) for both N sources,, induced at low external concentrations of N and/or low N status in the plant was confirmed. Ammonium negatively regulates nitrate uptake by modulating the expression of genes involved in this process. Plants under N deficiency (-N) exhibited a late regulation of HATS responsible for nitrate uptake. The lack of correlation between 15N influx and transcript accumulation of nitrate transporter genes suggests the existence of a post-transcriptional regulation of HATS in roots subjected to nitrate resupply. To characterize the remobilization process, plants were submitted to contrasting conditions of N availability to identify the mechanisms by which nitrate may be affected during this process. Despite the low efficiency of nitrate uptake and storage, sugarcane demonstrates the ability to use nitrate as N source. In N sufficient conditions (+N), ammonium and nitrate are used as N source. Under restriction of N, however, nitrate has increased flow in roots and stems, while ammonium remains as N source to young leaves by change in nitrate loading into the xylem. However, the source of the nitrate to be reduced and assimilated in leaves appears to be originated from the culm. Therefore, modulation of NRT transporters expression ensures nitrate allocation in sugarcane when N is limited in soils (AU)

• FAPESP's process: 13/02702-2 - Physiological characterization and gene expression profile of transportation during acquisition and nitrate remobilization in sugarcane (Saccharum spp.)
• Grantee: Luís Henrique Damasceno Serezino
• Support Opportunities: Scholarships in Brazil - Master