Expression of a putative high-affinity NO3- transporter and of an H+-ATPase in relation to whole plant nitrate transport physiology in two maize genotypes differently responsive to low nitrogen availability

Two maize genotypes differently responsive to nitrogen availability were characterized for their efficiency in nitrate accumulation via both the LATS (Low-Affinity Transport System) and HATS (High-Affinity Transport System) nitrate uptake systems. In addition, a full-length cDNA encoding a putative high-affinity nitrate transporter (ZmNrt2.1) was isolated and its expression evaluated in both the roots and leaves of the two maize genotypes, together with the expression of a maize H+-ATPase isoform (Mha1). The data showed the importance of the MATS (Inducible High-Affinity System) system efficiency as a physiological marker of adaptation to low input and suggested that the transcript accumulation of ZmNrt2.1 might be a key step for the regulation of MATS. However, ZmNrt2.1 transcription cannot account for the differences found between the two hybrids in terms of the activity of their respective iHATS and, as a consequence, of their adaptation to low input. Therefore, the involvement of some other transporter(s) or of some post-transcriptional/posttranslational mechanism of regulation affecting the efficiency of iHATS may be hypothesized. In addition, the data suggest that the transcription of the Mha1 gene may also be involved in the global efficiency of the iHATS system.