Polyamine regulation of growth and chilling tolerance of rice (Oryza sativa L) roots cultured in vitro

Seminal rice (Oryza saliva L. cv. Taichung Native 1) roots were grown in vitro to investigate the relationships among polyamine biosynthesis, root growth and chilling tolerance. At 25 degrees C, the level of free putrescine and the activities of arginine decarboxylase (ADC; EC 4.1.1.19) and ornithine decarboxylase (ODC; EC 4.1.1.17) increased as growth progressed while the levels of free spermidine/spermine and the activity of S-adenosylmethionine decarboxylase (SAMDC, EC 4.1.1.50) decreased. Exogenously applied putrescine, ranging from 0.01 to I mM, enhanced the elongation of roots grown at 25 degrees C whereas application of spermidine or spermine inhibited root elongation. alpha-Difluoromethylarginine (DFMA) at 5 mu M or alpha-difluoromethylornithine (DFMO) at 10 mu M inhibited the increase in root length and the levels of free putrescine at 25 degrees C; these effects were reversed by the addition of 1 mM putrescine. Roots exposed to 5 degrees C ceased growth and lost their re-growth ability after 9 days of chilling. The level of free putrescine and the activity of ADC in chilled roots increased with a peak at day 3 and then decreased to a plateau after 9 days. The levels of free spermidine and spermine increased after 9 days. When putrescine was applied at concentrations greater than 0.1 mM, chilled roots partially recovered their re-growth ability. Contrary to DFMO (10 mu M), DFMA (5 mu M) inhibited both the chilling-induced free putrescine increase and the re-growth ability of chilled roots, and these effects were reversed by 1 mM putrescine. These results suggest that polyamines are related to growth of rice roots cultured in vitro. The relationships between putrescine and chilling tolerance is discussed. (C) 1997 Elsevier Science Ireland Ltd.