GENETIC AND PHYSIOLOGICAL ANALYSIS OF A NEW LOCUS IN ARABIDOPSIS THATCONFERS RESISTANCE TO 1-AMINOCYCLOPROPANE-1-CARBOXYLIC ACID AND ETHYLENE AND SPECIFICALLY AFFECTS THE ETHYLENE SIGNAL-TRANSDUCTION PATHWAY

A population of M2 seedlings of Arabidopsis thaliana was screened for mutants that were insensitive to the ethylene precursor 1-aminocyclopr opane-1-carboxylate (ACC). Several independent lines were obtained and proved insensitive to both ACC and ethylene. Two lines were identifie d as alleles of a single recessive mutation, designated ain 1. Linkage analysis indicated that the ain 1 gene is located on chromosome 1, ad jacent to the cer5 marker and, therefore, genetically distinct from pr eviously identified ethylene resistance loci. General phenotypic aspec ts of ain1 mutants were similar to wild type. For both alleles, the le vel of insensitivity to ethylene at the seedling stage was indistingui shable in terms of elongation growth. In contrast, the gravitropic res ponse of ain1-1 seedlings was slower than that of wild-type and ain1-2 seedlings. At the adult stage, stress responses of mutants were simil ar to wild type. However, ethylene-induced leaf senescence was delayed in both mutants. In addition, we observed significant interallelic va riation in ethylene production rates. Growth inhibition experiments sh owed that the ain1 mutation does not confer resistance to other hormon es. Thus, ain1 most probably affects a step specific for the ethylene signal transduction pathway.