Root formation in ethylene-insensitive plants

Experiments with ethylene-insensitive tomato (Lycopersicon esculentum) and petunia Petunia x hybridal plants were conducted to determine if normal or adventitious root formation is affected by ethylene insensitivity. Ethylene -insensitive Never ripe (NR) tomato plants produced more belowground root m ass but fewer aboveground adventitious roots than wild-type Pearson plants. Applied auxin (indole-3-butyric acid) increased adventitious root formatio n on vegetative stem cuttings of wild-type plants but had little or no effe ct on rooting of NR plants. Reduced adventitious root formation was also ob served in ethylene-insensitive transgenic petunia plants. Applied 1-aminocy clopropane-1-carboxylic acid increased adventitious root formation on veget ative stem cuttings from NR and wild-type plants, but NR cuttings produced fewer adventitious roots than wild-type cuttings. These data suggest that t he promotive effect of auxin on advetitious rooting is influenced by ethyle ne responsiveness. Seedling root growth of tomato in response to mechanical impedance was also influenced by ethylene sensitivity. Ninety-six percent of wild-type seedlings germinated and grown on sand for 7 d grew normal roo ts into the medium, whereas 47% of NR seedlings displayed elongated taproot s, shortened hypocotyls, and did not penetrate the medium. These data indic ate that ethylene has a critical role in various responses of roots to envi ronmental stimuli.