The first successful induction of adventitious shoot buds on Santalum album L. leaves is reported. De novo shoots were induced directly on leaves without any callusing stage. A leaf length of 0.5-1.5 cm only showed bud inducing potential. Bud formation occurred on both MS and WPM basal media, although, liquid media were more responsive. Among the plant growth regulators, BAP at low concentrations (0.44 and 2.22 µM) was effective in this organogenetic process but exogenous auxin application failed to illicit a similar morphogenetic response. Epiphyllous shoot formation was more pronounced on leaf lamina in which the dorsal and ventral leaf surfaces were equally highly regenerative; the response, however, varied in different parts of the leaf.

https://journals.tubitak.gov.tr/botany/issues/bot-05-29-1/bot-29-1-6-0308-1.pdf

In vitro Regeneration of Sandal (Santalum album L.) from Leaves

An efficient and reproducible procedure is described for direct shoot regeneration using petiole and leaf explants of Withania somnifera (L.). The shoots were mainly induced from the distal end of the petiole, whereas in leaf explants, shoot regeneration was initiated from the basal part and wounded tissue. The regeneration medium that induced the highest numbers of shoots in the petiole and leaf explants was Murashige and Skoog (MS) medium supplemented with 2 mg/l N 6 -benzyladenine (BA) alone or with 0.1 mg/l a-naphthalene acetic acid (NAA). The frequency of shoot regeneration was greatly influenced by the type of explant, the carbon source, the orientation of the explant, and the basal medium used in the regeneration medium. Explants produced shoot buds and adventitious shoots within four weeks. Histological analysis of the regenerating shoots showed that the shoot buds emerged from sub epidermal parenchymal cells, with no intermediate callus formation. Plantlets were rooted on MS alone or MS containing different concentrations of 3-indolebutyric acid (IBA). The addition of 1 mg/l IBA to the medium was most effective in inducing root formation. The regenerated plantlets were acclimatized in the greenhouse and successfully transferred to the field, with a 90% survival rate. The acclimatized plants showed normal flowering and were not morphologically different from the seed-derived mother plants.

/pdf/direct-shoot-organogenesis-from-petiole-and-leaf-discs-of-3mnf81de5k.pdf

Direct shoot organogenesis from petiole and leaf discs of Withania somnifera (L.) Dunal

Shoot bud regeneration was obtained from isolated leaflets of Albizia procera cultured on MS medium with various concentrations of 6-benzyladenine (BA) and α-naphthaleneacetic acid (NAA) The highest numbers of adventitious buds were obtained on MS medium supplemented with 10 μM BA and 1 μM NAA The replacement of 7 g l-1 Difco bacto agar with 26 g l-1 Phytagel in the medium enhanced adventitious bud regeneration Further, addition of 15 μM silver nitrate promoted callus-free shoot regeneration from leaf explants The regenerated shoot buds were elongated on MS medium containing 001 μM BA and 1 μM NAA Rooting was obtained on modified MS medium supplemented with 2 μM IBA To our knowledge this is the first report of direct regeneration of shoots from leaflet explants in A procera, and should help facilitate genetic transformation in this species

Regeneration of plants from leaflet explants of tissue culture raised safed siris (Albizia procera)

Bud sporting, the consequence of sudden variations in gene expression of somatic cells, leads to the occurrence of phenotypically altered shoots in many vegetatively propagated plant species. In ornamentals, such as azalea (Rhododendron simsii), flower colour bud sports are appreciated as a valuable additional source of variation, and it is evident that both genetic and epigenetic mechanisms are involved in the creation of the whole colour range. Flowers exhibiting two-coloured petals, i.e. the margin is coloured differently than the central zone, characterize one of the sport types, namely picotees. This particular sporting type contributes to the enlargement of the available variation not only because of its coloration pattern but interestingly displays somatic polyploidy in its petals. The differently coloured petal margin is tetraploid while the rest of the corolla, as well as the entire plant are diploid. Aiming at introducing polyploidy in the completely diploid breeding collection, in vitro regeneration of tetraploid petal marginal tissue was performed. This led to the production of the first induced tetraploid Belgian azalea. The markedly increased robustness of the flowers as well as their polyploid status is exceptionally interesting for breeding programs.

Somatic polyploid petals: regeneration offers new roads for breeding Belgian pot azaleas

Flower colour variegation is not only a phenomenon of importance to horticulture, the phenotype involved is also often used as a scientific model system for the study of complex gene regulation processes. In the course of such studies on azalea, we observed a correlation between flower colour patterns, flower morphology and somatic polyploidy. Using high-resolution flow cytometry of nuclear DNA, the ploidy level was determined in flowers of different azalea sport families. Sports exhibiting variegated flowers with broad (>7 mm), differently coloured, petal edges (picotee type) proved to be tetraploid in the petal edge but diploid in the rest of the flower tissue. Neither flower colour pattern nor ploidy differences are periclinal chimeric in origin, but seem to be correlated with the topographic location of the cells within the flower tissue, i.e. the margin of the petals. The possible role of gene dosage effects and cell size involved in the remarkable correlation between somatic polyploidy, (flavonoid) gene expression and flower morphology is discussed.

Somatic polyploidy and its consequences for flower coloration and flower morphology in azalea

Rhododendron simsii ‘Hellmut Vogel’ was regenerated using different types of explants, auxins and cytokinins. After a callus induction phase, with 2,4-dichlorophenoxyacetic acid or α-naphthaleneacetic acid, adventitious shoot regeneration was obtained on a medium supplemented with thidiazuron or zeatin. With thidiazuron shoots were small and a subsequent elongation step was required before rooting. An elongation step was not required when zeatin was used. The duration of the callus induction phase was negatively correlated with the regeneration capacity.

M. Mertens

Papers

In vitro regeneration of evergreen azalea from leaves