Morphogenesis in Cultured Thin Layers and Pith Explants of Tobacco. II. Early Hormone-modulated Polyamine Biosynthesis

Abstract

Summary In order to gain deeper insight into the interrelationships between polyamines and hormones, superficial thin layers and pith explants, excised from the stem of tobacco ( Nicotiana tabacum L.) plants in the vegetative stage, were cultured under various hormonal conditions (IAA, IAA + BA, BA) and in a hormone-free medium, in the presence or in the absence of 100 μmol/L putrescine. In thin layers at 24 h, activation of putrescine biosynthesis via both arginine-(ADC) and ornithine decarboxylases (ODC) as well as free putrescine accumulation were detected in the IAA treatment, and via ADe alone in the presence of IAA + BA. BA caused an inhibition of or had no effect on putrescine biosynthesis. In pith explants, although some free putrescine accumulated in IAA treatment, no increase in its biosynthetic activity was detectable. No DAO activity could be detected in any treatment early in culture either in superficial or deep tissues. Exogenous putrescine did not affect this pattern. The modulation of polyamine biosynthesis by the different hormones in superficial and pith explants is discussed in relation to putrescine accumulation and oxidation and to early cytological events occurring in culture and previously described (Altamura et al., 1995).