The auxin-resistant dgt tomato mutant grows less than the wild type but is less sensitive to ammonium toxicity and nitrogen deficiency

The low-auxin-sensitivity tomato mutant, dgt, despite displaying reduced plant growth, has been linked to greater resistance to N deficiency. This led us to test the role of auxin resistance of dgt in NH4+ toxicity and N deficiency, compared to wild type tomato (cv. Micro-Tom, MT), grown in hydroponic media. A completely randomized design with three replications in a 2 × 4 factorial scheme was adopted, corresponding to the two tomato genotypes (MT and dgt), involving four nutritional treatments: NO3− (5 mM); NH4+ (5 mM); NO3− (5 mM) plus exogenous auxin (10 μM IAA); and N omission. The results show that NH4+ was toxic to MT but not to dgt. Under N deficiency, MT displayed a lower shoot NO3− content, a lower photosynthetic rate, and a decrease in both shoot and root dry weight. However, in dgt, no difference was observed in shoot NO3− content and photosynthetic rate between plants grown on NO3− or under N deficiency. In addition, dgt showed an increase in shoot dry weight under N deficiency. We highlight the role of auxin resistance in the adaptation of plants to NH4+ toxicity and N deficiency.