INFLUENCE OF ROOT NH4+ AND NO3- CONTENT ON THE TEMPERATURE RESPONSE OF NET NH4+ AND NO3- UPTAKE IN CHILLING SENSITIVE AND CHILLING RESISTANT LYCOPERSICON TAXA

We studied the influence of internal ammonium and nitrate content on the temperature response of ammonium and nitrate uptake in both chilling sensitive and chilling resistant tomatoes. Three taxa were examined: Lycopersicon esculentum Mill. cv. T-5, a chilling sensitive cultivar, Lycopersicon hirsutum Humb. and Bompl. LA1264, a wild, chilling sensitive accession from the lowlands of Ecuador, and Lycopersicon hirsutum LA1778, a chilling resistant accession from the highlands of Peru. Short exposures (4 h) of L. esculentum cv. T-5 to chilling temperatures irreversibly inhibited ammonium absorption for at least 6 h. Nitrate absorption in this taxon and ammonium and nitrate absorption in the L. hirsutum accessions recovered fully and immediately from such exposures. The chilling resistant accession, L. hirsutum LA1778, showed a lower Q10 for ammonium absorption (1.54 +/- 0.10, mean +/- s.e.) than its chilling sensitive relatives, L. hirsutum LA1264 (2.37 +/- 0.35) and L. esculentum cv. T-5 (1.92 +/- 0.11). The temperature response of nitrate absorption depended on internal nitrate status; plants grown at high levels of ammonium and nitrate (200 mmol m-3) showed higher Q10's for nitrate uptake (2.29 +/- 0.10) than those depleted of internal NO3- (1.86 +/- 0.12).