Regeneration in Streptocarpus Leaf Discs and its Regulation by Temperature and Growth Substances

Abstract

The formation of adventitious buds and roots in leaf discs of Streptocarpus x bybridus‘Constant Nymph’ were both stimulated by relatively low temperatures (12 and 18°C) applied to isolated discs or to the growing plants before leaf harvest. Auxins also promoted both bud and root formation, the optimum concentration for rooting always being one to two orders of magnitude higher than the optimum for budding. Cytokinins had only a small stimulatory effect on bud formation. At higher concentrations it was inhibitory and even counteracted the stimulatory effect of auxin on bud formation. As usual, root formation was inhibited by cytokinin. GA3 inhibited both bud and root formation but the inhibition was reversible by auxin. In presence of optimum auxin levels abscisic acid enhanced bud formation. It had little effect on root formation except for an inhibition at high concentrations. The effects of exogenous auxin and cytokinin suggest that Streptocarpus leaves have a high and non‐limiting level of endogenous cytokinin with auxin as the limiting factor for both root and bud formation. This would also explain the exceptionally high regeneration ability of this plant.

Micropropagation and assessment of genetic fidelity of Henckelia incana: an endemic and medicinal Gesneriad of South India

“…Similar callus formation before shoot proliferation has been reported in some Gesneriaceaea species (Godo et al 2010;Takagi et al 2011). The roots that occurred on the explants were short and hairy, which corroborates the earlier reports from other Gesneriaceae species (Appelgren and Helde Ola 1972;Lo 1997;Tóth et al 2004). …”

“…Moreover, shoot proliferation in control was more significant than all the concentrations of cytokinins used, which demonstrates that explants have high levels of endogenous cytokinins sufficient enough for shoot regeneration. These observations are in conformity with some gesneriads like Achimenes longiflora (Vlahos 1989) and Streptocarpus (Appelgren and Helde Ola 1972). The response of cytokinins on shoot regeneration in general was slow and less when compared to both the control and most of the auxin treatments.…”

“…These results suggest that low concentration of auxins favors higher shoot proliferation in H. incana. In the same way, induction of shoot formation by auxins has been reported in other gesneriads (Appelgren and Helde Ola 1972;Godo et al 2010;Ma et al 2011). …”

Environmental and Hormonal Effects in Micropropagation

“…Although culture temperature conditions have been frequently studied, little literature is available on the effects on cultures resulting from stock plant temperature treatments. An interaction was shown by Heide (1965) between stock plant temperature and growth regulator levels in begonia leaf segment cultures and Appelgren and Heide (1972) found that adventitious bud and root formation was stimulated when leaf segments of streptocarpus were cultured from stock plants grown at 12°C. According to Pierik and Ruibing (1973), the number of hyacinth bulblets was not affected by storage of the source bulbs at 25°C, but bulblet weight was increased if the bulbs were stored for 90 days.…”

“…Its influence on basic, physiological processes such as respiration, and on cell and organ formation is generally accepted. In plant tissue culture, optimum temperature may range as high as 32-35°C (Hughes, 1981), while reports of temperatures as low as lrC have been reported as optimum for streptocarpus (Appelgren and Heide, 1972). Using various species of begonia, several workers have reported varying responses to temperature.…”