Expression of a putative high-af®nity 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 ef®ciency in nitrate accumulation via both the LATS (LowAf®nity Transport System) and HATS (High-Af®nity Transport System) nitrate uptake systems. In addition, a full-length cDNA encoding a putative highaf®nity 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 iHATS (Inducible High-Af®nity System) system ef®ciency 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 iHATS. 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 ef®ciency of iHATS may be hypothesized. In addition, the data suggest that the transcription of the Mha1 gene may also be involved in the global ef®ciency of