Expression analysis of Nar1 and Nrt in U. maydis sporidia. Transcript abundance was determined using specific probes against Nar1 (top) and Nrt (middle) at 1, 2, 3, 4, 6, 24, and 48 h upon the transfer of SG200 and ΔN-Nit2 sporidia from ammonium minimal medium to minimal medium containing ammonium, ammonium and nitrate, nitrate, or no nitrogen source. Ammonium and nitrate concentrations in the media were 0.3% (wt/vol). As a loading control, abundance of 18S rRNA was determined (bottom).