Methylglyoxal(bis‐guanylhydrazone) inhibition of organogenesis is not due to S‐adenosylmethionine decarboxylase inhibition/polyamine depletion in tobacco thin layers

Abstract

Previous results indicated that in shoot‐forming tobacco thin layers the putative inhibitor of S‐adenosylmethionine decarboxylase (SAMDC, EC 4.1.1.21) activity methylglyoxal(bis‐guanylhydrazone) (MGBG) inhibited meristemoid/primordia formation while enhancing conjugated polyamine accumulation and ethylene biosynthesis, thus showing an inverse relationship between the two phenomena ( Scaramagli et al. 1999). In order to better understand how MGBG causes polyamine overproduction and by using the same model system, we further examined the effect of 0.5 mM MGBG on the incorporation of labelled methionine into spermidine and spermine, on SAMDC transcript levels and activity and on putrescine oxidising (DAO) activity at different times in culture. MGBG‐induced ethylene accumulation was also evaluated by gas chromatography (GC). In shoot‐forming controls (grown on a medium supplemented with IAA+BA) label was mainly incorporated into free spermidine (82–86% of the total amount incorporated into polyamines) while only 6–12% of radioactivity was recovered in free spermine. Some label was also found in putrescine. In the presence of MGBG, spermidine biosynthetic capacity was enhanced throughout the culture by 28–45% compared with controls. The same occurred for spermine and putrescine. MGBG‐enhanced spermidine synthesis was supported by increased SAMDC activity (days 1–2) and higher levels of SAMDC message (days 1–7). On the contrary, the effect of the drug on putrescine oxidation was inhibitory starting from day 2. These results, together with the previous ones, suggest that MGBG, in fact, does not behave as a SAMDC inhibitor in shoot‐forming tobacco thin layers and that its negative effect on organised growth is not due to SAMDC inhibition/polyamine depletion.

Changes in polyamine levels during growth of a red-tide causing phytoplanktonChattonella antiqua(Raphidophyceae)

“…On the other hand, MGBG does not behave as a SAMDC inhibitor in tobacco cells, and both intracellular polyamine levels and SAMDC activity increased when treated with MGBG (Hiatt et al, 1986;Scaramagli et al, 1999). Although MGBG inhibits in vitro SAMDC activity, the effects of MGBG on endogenous polyamine levels are contradictory and seem to be dependent upon the plant material.…”

Do exogenous polyamines have an impact on the response of a salt-sensitive rice cultivar to NaCl?

“…MGBG as an inhibitor of SAMDC, was supposed to induce a similar increase in Put but this was not confirmed in rice and this inhibitor therefore could not be recommended for this purpose. It has been reported by Scaramagli et al (1999) that in some experimental systems, MGBG is not specific for inhibition of SAMDC and does not always lead to Put accumulation.…”

Polyamine metabolism is upregulated in response to tobacco mosaic virus in hypersensitive, but not in susceptible, tobacco

“…Putrescine oxidising (DAO, EC 1.4.3.6) activity was assayed by a radiometric method based on the production of [ 14 C]Δ 1 ‐pyrroline from labelled putrescine as previously described (Scaramagli et al. , 1999a).…”