Auxin and cytokinin modify methyl jasmonate effects on polyamine metabolism and ethylene biosynthesis in tobacco leaf discs

In several in vitro systems, treatment with methyl jasmonate (MJ) stimulates polyamine biosynthesis as well as accumulation of acid-soluble and -insoluble conjugated polyamines. This effect is attributed to changes in gene expression and enzyme activity of arginine decarboxylase (ADC), ornithine decarboxylase (ODC) and S-adenosylmethionine decarboxylase (SAMDC). In the present study, we used tobacco (Nicotiana tabacum L. cv. Samsun) leaf discs to investigate the interaction between this MJ-induced response and those triggered by indole-3-acetic acid (IAA), N-6-benzyl adenine (BA) and ethylene. Our results indicate that MJ-induced accumulation of conjugated polyamines is further stimulated by auxin and counteracted by BA. The MJ-induced stimulation of ODC and SAMDC, but not ADC, mRNA levels was diminished by IAA +/- BA, whereas the corresponding enzyme activities were further enhanced in the presence of hormones. MJ enhanced ethylene production only when combined with hormones, and this trend was reflected in 1-aminocyclopropane-1-carboxylate oxidase transcript levels. Results suggest that the induction by MJ of conjugated polyamine levels, and of the polyamine biosynthetic genes and activities are differentially modulated by hormones, and that ethylene does not seem to be directly involved in this response. (C) 2003 Elsevier Science Ireland Ltd. All rights reserved.