Effects of polyamines on shoot and root development in arabidopsis seedlings and carnation cultures

Polyamines, a class of aliphatic amines, are active in the growth and development of bacteria, animals, and plants. To better understand their physiological role in plants, we used spermidine and the inhibitor of SAMDC to analyze the developmental patterns of roots and shoots fromArabidopsis seedlings and in-vhro carnation shoot cultures. We also monitored mRNA levels of the polyamine biosynthetic gene after adding various phytohormones to the growing media. Treating wildtypeArabidopsis seedlings with polyamine resulted in greater growth after four weeks; 1 mM spermidine increased root lengths by 39% and seedling weights by 44%. Spermidine was more effective in enhancing root growth in thedet2 mutants than in the wild-type plants. In contrast, MGBC, an irreversible inhibitor of SAMDC activity, resulted in root lengths that were 29% of the controls, as well as seedling weights that were only 77% of normal. In our carnation cultures, shoot-growth rates were severely reduced by both spermidine and MGBG; root growth was also markedly inhibited by treatment with spermidine. Transcripts ofADC andSAMDC were significantly greater in cultures treated with kinetin and IAA, with levels being higher with the former. Previous research has shown that sensitivity and the appropriate cellular content for polyamines vary among plant species, and may also be organ-or tissue-specific Polyamines may play an important developmental role because of their potentially stimulatory effects on phytohormonal signaling and/or synergism.