In contrast to some previous reports on the growth of the ABA-deficient wilty mutants of tomato, growth was at least as rapid in the mutants as in the wild type, as long as an adequate plant water status was maintained by growing the plants under mist. Moreover, shoot extension was greater and the rate of leaf production more rapid in the mutants. Stomatal changes in response to environment and to time in the light-dark cycle were generally similar in both wilty mutants and the wild type, though the wild-type were generally more closed. Grafting experiments confirmed that the genotype of the shoot was dominant in determining stomatal aperture, though wild-type rootstocks could cause a slight reduction in the stomatal conductance of mutant leaves. The effect on plant water relations of draughting only part of the root system was investigated in a ‘split-root’ experiment. Withholding water from only part of the root system was found to lower significantly the mean leaf water potential, even though the potential evaporation rate was kept very small.

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