Polyamine conjugate levels and ethylene biosynthesis: inverse relationship with vegetative bud formation in tobacco thin layers

Abstract

The effects of two inhibitors of polyamine (spermidine and spermine) biosynthesis, cyclohexylamine (CHA; 5 and 10 mM) and methylglyoxal(bis‐guanylhydrazone) (MGBG; 0.1, 0.5 and 1 mM), on the organogenic response in vegetative bud‐forming tobacco (Nicotiana tabacum L. cv. Samsun) thin layer explants were evaluated micro‐ and macroscopically at different times during culture. The final number of buds formed and the percentage of organogenic explants was significantly reduced by both inhibitors, but much more so by MGBG than CHA. This inhibitory effect was already evident in MGBG‐treated explants on day 5, in terms of the number of meristemoids per explant. On the contrary, in the presence of CHA, the number of meristemoids on day 5 was higher than that in the controls. Between days 9 and 13, meristemoid formation slowed down considerably in inhibitor‐treated explants compared with controls. On day 13, the number of bud primordia was similar in control and CHA‐treated explants, but significantly lower in MGBG‐treated explants. This inhibitor also induced peculiar cytohistological events, such as a reduced formation of oval‐shaped cell aggregates on the explant surface and more frequent cases of nucleolar extrusion, while CHA led to the appearance of hypertrophic epidermal cells; callus formation at the basal end of the explant and xylogenesis were also affected by the inhibitors. Ethylene biosynthesis, measured as [ C]methionine incorporation, was stimulated 2‐ (day 2) to 3‐fold (15 h) by 0.5 mM MGBG, whereas CHA (10 mM) had little effect and aminoethoxyvinylglycine (AVG; 0.1 μM), an ethylene synthesis inhibitor, was strongly inhibitory. In control explants, the incorporation of labelled methionine into ethylene and spermidine followed an inverse trend up to day 8. In these explants, free putrescine increased 32‐fold and spermidine increased about 10‐fold between days 0 and 8. Trichloroacetic acid (TCA)‐soluble conjugated putrescine also accumulated dramatically during culture. While CHA provoked a decline in spermidine levels, MGBG caused an unexpected increase in free spermidine and spermine titres; however, its most conspicuous effect was on the further enhancement of putrescine conjugate accumulation, while CHA and AVG had the opposite effect. Results are discussed in view of establishing a putative link between MGBG‐enhanced ethylene synthesis, increased conjugate titres and inhibition of meristemoid formation.

Role of polyamines in adventitious shoot morphogenesis from cotyledons of cucumber in vitro

“…AgNO 3 inhibits ethylene's action by competitively binding to ethylene receptors (Chi et al, 1991). Although many analyses between them, as well as their relationships with morphogenesis during culture in vitro have been made, the results are not consistent (Cho and Kasha, 1989;Scaramagli et al, 1999;Irene et al, 2003). Our previous research showed when cotyledonary explants of cucumber are cultured in vitro, the floral or adventitious buds could be induced by different levels of the endogenous polyamines, depending on the hormonal composition of the medium (Zhu et al, 1999).…”

“…Spermidine (Spd) and spermine (Spm) and their diamine precursor putrescine (Put) are most common in plants. Accumulative evidences of culture in vitro indicate that PAs play important roles in somatic embryogenesis in carrot cell (Bastola and Minocha, 1995) and Dactylis glomerata L. (Li and Burritt, 2003), in bud formation in thin layer explants of tobacco Kaur-Sawhney et al, 1986;Scaramagli et al, 1999), in shoot regeneration from passiflora leaves (Desai and Metha, 1985) and cotyledonary explants of Chinese cabbage (Cho and Kasha, 1989) and melon (Tian et al, 1994), and in senescence of rose leaves (Shweta and Nagar, 2003). In addition, PAs are also closely related with the growth and differentiation of plant cells.…”

“…The effects of ethylene on physiological processes of plants are universal (Chi et al, 1991;Scaramagli et al, 1999). When cultured in vitro, the differentiation of plant cells is correlated with the involvement of ethylene, whose biosynthesis interacts with PA biosynthesis.…”

Dynamics of physiological and biochemical changes during somatic embryogenesis of Acca sellowiana

“…3B). The balance among free and conjugated PA forms may be critical in different developmental processes (Torrigiani et al 1987), and when the conjugated PA levels are high, organogenesis proceeds (Scaramagli et al 1999). On the other hand, high levels of Put at the beginning of somatic embryogenesis are related to the ability of competent cells to develop somatic embryos (Nieves et al 2003).…”

Ethylene and polyamine interactions in morphogenesis of Passiflora cincinnata: effects of ethylene biosynthesis and action modulators, as well as ethylene scavengers

“…The greatest organogenesis frequency in the present study occurred in the culture supplemented with AVG, and this treatment showed the lowest conjugated levels for all the polyamines. The balance among the free and conjugated forms may be critical for different development processes (Torrigiani et al 1987), and when the conjugated polyamine levels are high, organogenesis proceeds (Scaramagli et al 1999).…”