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ABSTRACT: Long-sized oligogalacturonides (OGs) are cell wall fragments that induce defence and developmental responses. The Ca(2+)-dependent "egg-box" conformation is required for their activity, and polyamines may prevent them from adopting this conformation. Although OGs are known to inhibit auxin-induced growth processes, their effect on cytokinin-induced ones requires investigation. In the present work OGs were shown to promote cytokinin (benzyladenine, BA)-induced vegetative shoot formation from tobacco leaf explants, independent of the presence of CaCl(2) in the medium and of auxin (indoleacetic acid, IAA) supply. The effect of polyamines, putrescine (PU) and spermidine (SD) supplied with/without their biosynthetic inhibitors (DFMO, CHA) was also investigated, and showed that spermidine enhanced adventitious vegetative shoot formation, but only on medium containing Ca(2+) and IAA. Treatments with inhibitors blocked this promotive effect. OGs did not alter free polyamine concentrations, but caused a moderate increase of conjugated ones, and exhibited an early inhibitory effect on polyamine biosynthetic gene expression. OGs, but not SD, caused long-term changes in calcium-associated epifluorescent signals in the cell walls, and, later, inside the cells of specific tissues. Electron microscopy analysis (ESI system) demonstrated that calcium accumulated in the cell walls and vacuoles of OG-cultured explants. The relationship between OGs, cytokinin, calcium, and polyamines in adventitious vegetative shoot formation is discussed.
Planta 04/2008; 227(4):835-52. · 3.00 Impact Factor
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ABSTRACT: Thin cell layers excised from tobacco (Nicotiana tabacum L. cv. Samsun) stem internodes, with an appropriate exogenous hormonal balance, were able to form a greater number of roots, and in a larger percentage of the explants (93%) than when they were excised from pedicels (40%). The developmental sequence of root formation and explant growth were followed by histological analysis. Free and bound [trichloroacetic acid (TCA)-soluble and -insoluble] putrescine and spermidine increased in the explants, particularly when root meristemoids appeared. These meristemoids originated in the superficial (day 6 in culture) or deep (days 10–11) layers and inside the newly formed callus (day 25). At those times, TCA-soluble and, to a lesser extent, TCA-insoluble bound putrescine predominated over the other polyamines. Spermine was always present in trace amounts. Polyamines decreased again when root and callus formation was completed (day 30). The involvement of these three classes of polyamines (free, TCA-soluble and -insoluble) in morphogenic processes is discussed.
Physiologia Plantarum 04/2006; 77(3):294 - 301. · 3.11 Impact Factor
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ABSTRACT: The organogenic potential of thin layer stem explants of non-reproductive tobacco plants was tested on a hormone-free medium and under various hormonal conditions. A comparison was made between thin layers excised from normal and transgenic plants at the same developmental stage. The transgenic plants were transformed by insertion of TR- and TL-DNA from Agrobacterium rhizogenes 1855 root-inducing plasmid. The aim was to identify hormonal conditions capable of stimulating the expression of the flowering competence present in the differentiated stem tissues at the induced stage before any visible sign of transition to reproductive development. Flower neoformation, observed at the end of the culture period (day 25), occurred on untransformed thin layers only with kinetin treatment. Explants from transgenic plants showed flower bud regeneration on hormone-free medium, indoleacetic acid alone (1 μM), kinetin alone (1 μM), and most abundantly on indoleacetic acid plus kinetin (1 μM each). No flower formation was observed on indolebutyric acid plus kinetin (10 μM and 0.1 μM, respectively) in both normal and transgenic explants. The latter treatment enhanced rooting instead, above all in the transgenic explants. On hormone-free medium vegetative bud formation was well expressed both by untransformed and transgenic explants, and enhanced by the combined, equimolar concentrations of indoleacetic acid and kinetin.The results show that cytokinin allows flowering in florally determined stem explants from normal plants. In the transgenic explants, the flowering response increases when indoleacetic acid is added to cytokinin, thus suggesting a role for auxin in enhancing the expression of the florally determined state in thin cell layers of non-reproductive plants.
Physiologia Plantarum 04/2006; 84(4):555 - 560. · 3.11 Impact Factor
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ABSTRACT: Pith explants excised from the apical stem internodes of vegetative, flowering, and fruiting tobacco plants were cultured
on hormone-free medium in the presence or absence of CaCl2 (3 mM). The aim was to determine the role of exogenous calcium (Ca2+), applied at the concentration normally present in the Murashige and Skoog (1962) medium, in organ formation obtainable in
the absence of the exogenous hormonal input. Exclusive formation of vegetative buds was obtained from explants excised from
vegetative plants (pure vegetative programme); vegetative buds and flowers (and occasionally roots) on the same sample were
obtained from explants from flowering plants (mixed flowering programme); whereas roots, very occasionally associated with
vegetative buds and flowers on the same sample, were obtained from explants from fruiting plants (mixed rooting programme).
Histological analysis showed that the organs always exhibited indirect regeneration. Exogenous Ca2+ promoted the formation of meristemoids and the first phases of their growth into organs, but did not change the realization
of the organogenic programme and did not affect callogenesis. Instead, the influence of exogenous Ca2+ changed with the programme, when considering the last phases of organ growth (i.e., macroscopic development and elongation),
and the appearance of morphological anomalies in the organs.
Plant Cell Tissue and Organ Culture 03/2004; 77(1):1-10. · 3.09 Impact Factor
