Polyamine Metabolism, and Root Formation in Developing Tobacco Plants

Abstract

The content of water-insoluble amine conjugates (di-feruloylputrescine, di-feruloyl- spermidine, feruloytyramine) decreased drastically during tobacco germination, concomitantly with a rapid increase in free polyamines (putrescine, spermidine, tyramine). Neither DFMA nor DFMO inhibited the emergence of the radicle, which is considered to be the end of the germination process, nor where the putrescine and spermidine titers modified during the first two days. We present evidence that ADC and ODC regulate putrescine biosynthesis at different stages of tobacco root development, with ADC being active early in development and ODC later. Arginine decarboxylase reached a peak on day 3 of germination (Fig. 1) and was required for root elongation. Ornithine decarboxylase activity peaked 3 days after emergence of the radicle (Fig. 2), and was required for subsequent root development and branching. When ADC action was blocked by DFMA, polyamine diminished only during the first few days of development; when agmatine or putrescine were added, normal polyamine titers and growth were restored. The effects of DFMA were concentration dependent. DFMO promoted root elongation during the first few days of seedling development. This effect of DFMO is related to the observed enhancement of plant ADC and accumulation of polyamines. Fundamental changes in growth and tobacco root development were associated with inhibition of ODC by DFMO (root elongation was stopped, and no, or only limited ramification, was observed during the whole period of development). They correlated with the inhibition of the production of free polyamines, and with inhibition of putrescine conjugates. Our results lead to the following conclusions: ADC leads to the production of free polyamines which are required for growth by cell expansion; ODC is required for cell division and differentiation; putrescine conjugates are important in