Fig 4. Repression of NIA1 and NRT2.1 in the 42.49 mutant is partially insensitive to treatments with NO donors, A23187 and IBMX.

NIA1 and NRT2.1 transcript levels were quantified by qRT-PCR in the 704 parental and in the 42.49 mutant after treatment with (A) and (B) DEA NONOate, (C) and (D) SNP and FeCN chemical control, (E) A23187, and (F) IBMX. The strains were originally grown in medium containing NH₄⁺ 8 mM as the sole nitrogen source until the cultures reached the exponential growth phase. Cells were then washed and transferred to the induction medium containing NO₃^- 100 μM plus different chemicals at the indicated concentration. The NO₃^- concentration used in this experiment was lower compared to previous experiments because, among other reasons, the chemicals are less potent repressors of gene expression than ammonium. These technical issues are discussed in the Material and Methods section. Samples were harvested 1 hour after treatment. Results are expressed in % relative to the untreated control.