The amount of polyamines (such as putrescine, sper-midine, and spermine) increased under environmental stress conditions. We used transgenic technology in an attempt to evaluate their potential for mitigating the adverse effects of several abiotic stresses in plants. Be-cause there is a metabolic competition for S-adeno-sylmethionine as a precursor between polyamine (PA) and ethylene biosyntheses, it was expected that the antisense-expression of ethylene biosynthetic genes could result in an increase in PA biosynthesis. An-tisense constructs of cDNAs for senescence-related 1-aminocyclopropane-1-carboxylic acid (ACC) synthase (CAS) and ACC oxidase (CAO) were isolated from carnation flowers that were introduced into tobacco by Agrobacterium-mediated transformation. Several trans- genic lines showed higher PA contents than wild-type plants. The number and weight of seeds also increased. Stress-induced senescence was attenuated in these transgenic plants in terms of total chlorophyll loss and phenotypic changes after oxidative stress with hydro-gen peroxide (H2O2), high salinity, acid stress (pH 3.0), and ABA treatment. These results suggest that the transgenic plants with antisense CAS and CAO cDNAs are more tolerant to abiotic stresses than wild-type plants. This shows a positive correlation between PA content and stress tolerance in plants.

Keywords: Abiotic Stress, ACC Synthase, Antisen, ACC Oxidase