Cytological analysis of the bulblet initiation and development in Lycoris species

Abstract

Lycoris is a genus of flowering bulbs belonging to the Amaryllidaceae family; this genus includes approximately 20 native species that are mainly distributed in East Asia. In recent years, Lycoris has attracted increasing attention due to its high ornamental, medicinal and ecological value, which has also caused considerable exploitation of wild bulbs. Enhanced propagation could lead to the restoration of wild populations and more efficient commercial production. Here, we studied and compared the process of bulblet propagation in Lycoris sprengeri Comes ex Baker and Lycoris aurea (L'Herit) Herb. under medium-free incubation conditions. The propagation process was divided into four stages based on systematic observations: 0–3days after the cutting treatment (DAT) (competence stage), 3–9 DAT (axillary bud initiation and elongation), 9–15 DAT (bulblet formation) and 15–45 DAT (bulblet development and expansion). The active mobilization of starch granules was studied using light and transmission electron microscopy, and the starch granules in the adaxial side of the outer scales began to decompose within 12h after the cutting treatment. An axillary bud was formed from the axils of the scales on the abaxial surface and then gradually formed the bulblet. Lycoris sprengeri showed a greater ability to form bulblets than L. aurea (∼1-5 versus ∼1-2 bulblets/bulb section, respectively), although bulblets were more evenly distributed within the mother bulb in L. aurea. In conclusion, the novel and detailed information provided in this study contributes to our understanding of bulblet initiation and development in Lycoris at the morphological, cellular and subcellular levels. Additionally, the general duration of the initial “competence-response” stage was identified. This information will facilitate further research into the molecular mechanisms and regulatory networks underlying bulblet initiation and development.