Ornithine Decarboxylase, Polyamines, and Pyrrolizidine Alkaloids in Senecio and Crotalaria

Abstract

When tested for ornithine and arginine decarboxylases, pyrrolizidine alkaloid-bearing Senecio riddellii, S. longilobus (Compositae), and Crotalaria retusa (Leguminosae) plants exhibited only ornithine decarboxylase activity. This contrasts with previous studies of four species of pyrrolizidine alkaloid-bearing Heliotropium (Boraginaceae) in which arginine decarboxylase activity was very high relative to that of ornithine decarboxylase. Unlike Heliotropium angiospermum and Heliotropium indicum, in which endogenous arginine was the only detectable precursor of putrescine channeled into pyrrolizidines, in the species studied here using difluoromethylornithine and difluoromethylarginine as the enzyme inhibitors-endogenous ornithine was the main if not the only precursor of putrescine converted into the alkaloid aminoalcohol moiety. In S.riddeliji and C. retusa at flowering, ornithine decarboxylase activity was present mainly in leaves, especially the young ones. However, other very young organs such as inflorescence and growing roots exhibited much lower or very low activities; the enzyme activity in stems was negligible. There was no correlation between the enzyme activity and polyamine or alkaloid content in either species. In both species only free polyamines were detected except for C. retusa roots and inflorescence-with relatively very high levels of these compounds-in which conjugated putrescine, spermidine, and spermine were also found; agmatine was not identified by HPLC in any plant organ except for C. retusa roots with rhizobial nodules. Organ-or age-dependent differences in the polyamine levels were small or insignificant. The highest alkaloid contents were found in young leaves and inflorescence.Our previous study on PA '- the same borages were able to decarboxylate exogenous Orn to Put that in turn was converted into necines. Thus, in vivo transformation of an exogenous putative precursor does not always indicate the compound formed in situ that normally serves as a precursor. This is especially true in the case of Put, which can derive not only from Orn but also from Arg via Agm, the product of Arg decarboxylation by ADC. Our attempt to identify the in situ precursor(s) of the Put channeled into pyrrolizidines in Senecio vulgaris were unsuccessful due to the extremely low PA content of the shoots.We report here the effects of DFMO and DFMA on necine biosynthesis in S. riddellii, S. longilobus (Compositae), and Crotalaria retusa (Leguminosae) plants. These species occasionally produce extremely high levels of PAs, up to 9 to 17% of leaf dry weight (23). In previously analyzed samples of S. riddellii and S. longilobus plants from New Mexico the PA contents were about 1.5 and 2.8%, respectively (10). Since there is little information about polyamines, including Put, ADC, and ODC activities, or the site(s) of alkaloid biosynthesis in PA-bearing plants, and since such information is available only for Heliotropium (5, 7-9), a more detailed examination of PA-bearing plants seemed important. Flowering...

Glass beads as a solid matrix in in vitro study of the role of polyamines in cold hardiness of white clover

“…Evidence in the literature suggested that these inhibitors can be uptaken by callus [3,5], cell suspension [4] and protoplast cultures [7], by root fragments [12] and decapitated shoots [2]. We found in media solidified with 0.8% agar a poor uptake of ~4C-DFMO by rooted white clover plantlets.…”

A rapid and reliable procedure for extraction of cellular polyamines and inorganic ions from plant tissues

“…Most of the published work on extraction of polyamines from various plant tissues involves homogenization in cold perchloric acid (PCA) or trichloroacetic acid (TCA) using either one of the following: a) chilled mortar and pestle with liquid nitrogen, b) polytron or tissumizer, or c) small conical ground-glass homogenizers with matching pestles (Birecka et al 1988, Faure et al 1991, Kushad and Yelenosky 1987, Maki et al 1991, Meijer and Simmonds 1988, Minocha et al 1991, 1992, Nielsen 1990, Rastogi and Davies 1989, Torrigiani et al 1987. Even though any of these extraction procedures is not too complicated when relatively few samples need to be processed, they are definitely time consuming and occasionally noisy due to the use of polytron for longer periods.…”