The chilling sensitivity of root ammonium influx in a cultivated and wild tomato

A chilling episode of a few hours damaged root ammonium absorption in a cultivated tomato ( Lycopersicon esculentum cv. T-5), but not in a wild congener from high altitudes ( Lycopersicon hirsutum LA1778). In the cultivar, ammonium influx was strongly temperature dependent and showed the residual effects of chilling, whereas ammonium efflux was nearly temperature invariant and showed no persistent effects. A 2 h exposure to 5 °C significantly depressed subsequent ammonium absorption at 20 °C, and about 12 h at 20 °C was required for recovery. For both the cultivated and wild species, rerooted cuttings were slightly less sensitive to chilling than seedlings. The relative inhibition (mean ± SE) of ammonium absorption before and after chilling was 58·4 ± 2·5% for the cultivated species and 29·0 ± 9·1% for the wild species. The F₁ hybrid between the species showed a relative inhibition of 52·4 ± 3·6%, suggesting that chilling sensitivity may be dominant. In a backcross of the hybrid to L. esculentum , the phenotypic distribution of the relative inhibition of ammonium absorption indicated that this trait is segregating.