Propagation,growth, and carbohydrates of <Emphasis Type="Italic">Dendrobium</Emphasis> Second Love (Orchidaceae) <Emphasis Type="Italic">in vitro</Emphasis> as affected by sucrose,light, and dark

In general, plant material grown in vitro has low photosynthetic ability to achieve positive carbon balances. Therefore, a continuous supply of carbohydrates from the culture medium is required, and sucrose has been the most commonly used carbon source. In this paper, we investigate the effects of different sucrose concentrations and the presence and absence of light on the endogenous levels of soluble carbohydrates and starch as well as on the proliferation and growth of Dendrobium Second Love (Orchidaceae) in vitro. The possibility of using etiolated stem segments as a means for micropropagating this hybrid was also verified. The results obtained indicated that the presence and absence of light and the sucrose concentrations used influenced the amounts of soluble carbohydrates and starch and the proliferation of D. Second Love shoots and roots. An increase in sucrose concentration caused a progressive increase in the amounts of total carbohydrates and starch. Under both light conditions, sucrose was the main sugar found in the shoots followed by glucose and fructose. The addition of sucrose to the culture medium up to 2% and 4% was advantageous to the number of shoots produced per explant and the root longitudinal growth in the presence and absence of light, respectively. Shoot and root dry matter and the number of roots formed per explant increased as sucrose concentration was raised up to 6% in both light treatments. The use of dark-grown shoot segments proved to be a useful and reliable alternative for the micropropagation of this hybrid.     

In vitro flowering of Dendrobium

Dendrobium plants are the most frequently used orchids to study the process of in vitro flowering. Among the various environmental cues and plant growth regulators employed thus far, cytokinins have shown the most prominent effects on the transition from vegetative to reproductive stage. A clear correlation between flowering establishment and enhancement of endogenous cytokinins has been observed. However, the experimental utilization of a large amount of different Dendrobium species and hybrids, combined with a large diversity of variable media types and media compositions make interpretation of flowering control in the in vitro environment difficult. The combination of a specific model Dendrobium in vitro regeneration system or protocol with a simple, but well defined culture medium, could contributed, to some degree, to reaching a clearer consensus about the physiological and molecular mechanisms controlling the Dendrobium flowering phase change.