In the present study, biomass production was used to calculate NUE for a collection of Italian tomato cultivars and one from California
supplied with NO3 grown in hydroponics and sand to identify contrasting NUE genotypes. Two lines representing consistently high and low NUE ranges were selected for a more detailed analysis comparing their morphological, physiological and
molecular traits growing in hydroponic culture. Nitrate transporter activity measurements using NO3-elicited changes in root cell membrane potential and 15N influx, tissue NO3 reductase (NR) activity, and root morphology were evaluated. Finally, the expression
of some assimilatory (NR) and NO3 transporter (SlNPF6.3, SlNRT2.1, SlNRT2.3 and SlNAR2.1) genes was compared. This analysis
identified some differences between the two contrasting phenotypes and these traits may be used as potential markers for tomato
breeding to select for improved NUE.