In vitro flowering on leaf explants of Streptocarpus nobilis. The influence of culture medium components on vegetative and reproductive development

Abstract

Streptocarpus nobilis (C.B. Clarke) became photoperiodically more responsive to short days with increasing age. Leaf explants from photoperiodically induced plants were all organogenically competent when cultured on Murashige and Skoog medium in 8-h photoperiods. Both vegetative and flower buds were developed; the maximum level of in vitro flowering occurred in response to 6-benzylaminopurine (BAP), but only 50% of the explants produced flowers. 3-Indoleacetic acid (IAA) (1 × 10−7 to 1 × 10−6 M) inhibited in vitro flowering. A nutrient medium was devised which allowed the expression of flowering on 100% of explants. The expression of vegetative or reproductive development was strongly influenced by the concentrations of media nutrients. On high-KNO3 (20 mM) – high-sucrose (100 mM) medium vegetative development was favoured and flower buds were produced on only 28% of explants. On low-KNO3 (2 mM) – low-sucrose (15 mM) medium only flower buds were developed on all explants. On low-KNO3 (5 mM) medium organogenesis was also affected quantitatively by the sucrose concentration; organogenesis was reduced from 90% explant response on 25-mM sucrose medium to 52% explant response on 100-mM sucrose medium. The most rapid flowering response to low-KNO3 (2 mM) – low-sucrose (15 mM) medium was obtained on explants from leaves of axillary branches. Flower buds were formed on the main vein at the proximal region of the explant. This high response at a predictable location provides a useful system for investigating flowering.