Study to develop a new strategy to in vitro propagation of Cattleya and Cymbidium (Orchidaceae) using the lateral buds of etiolated shoot

Author(s)

Lia Chaer

• Document type: Master's Dissertation
• Press: São Paulo.
• Institution: Universidade de São Paulo (USP). Instituto de Biociências (IBIOC/SB)
• Defense date: 2012-06-15

Examining board members

Gilberto Barbante Kerbauy; Helenice Mercier; Rogério Mamoru Suzuki

• Advisor: Gilberto Barbante Kerbauy

Abstract

Catasetum fimbriatum (Morren) Lindl. is an epiphytic orchid that has been studied since 1990 in our Laboratory. Plants of this genus have the peculiarity of being easily propagated, using the lateral buds of its etiolated shoot. This is possible because the shoot apical meristem shows a sustained activity when kept in darkness, resulting in an expressive shoot elongation. When the etiolated nodal segments are incubated under light, they rapidly form new plants. This micropropagation process dismisses the application of any plant growth regulators, representing an efficient in vitro multiplication method. The aim of this study was to apply the existing knowledge about the physiology of dark-grown C. fimbriatum plants, to other two genera, Cymbidium and Cattleya, intending to characterize the role of ethylene, gibberellin and nitric oxide in the signaling of shoot elongation process of these plants. C. fimbriatum and Cymbidium plants were obtained by micropropagation technique, using etiolated nodal segments, whereas Cattleya plants were obtained by assimbiotic germination. After 3 months, these plants were incubated in the dark under different levels of concentration of gibberellin (GA), ethylene, nitric oxid (NO), paclobutrazol (PA, inhibitor of gibberellin biosynthesis) and 1-methylcyclopropene (1-MCP, inhibitor of ethylene perception),. After 30 and 60 days, the treatments effects were measured through the number of nodal segments of the stolons, shoot size, and wet and dry mass. Ethylene and CO2 contents were determined using gas chromatography. The three studied genera showed different responses to dark incubation and treatments. Cattleya was not able to recover shoot apical meristem (SAM) activity and its phenotype remained unaltered, maintaining foliar growth until the end of the treatment. C. fimbriatum originated stolons from the base of the pseudobulb, forming etiolated shoots. On the other hand, Cymbidium showed a different meristematic activity, giving rise to an elongated stem from the apical end of the pseudobulb within the first 30 days of the experiment. GA promoted a significant increase in stem elongation in C. fimbriatum whereas in Cymbidium plants this parameter was inhibited at the highest level of hormone. PA and 1-MCP reduced stem elongation in both C. fimbriatum and Cymbidium plants. Ethylene treatment increased the development of lateral buds and their branching in C. fimbriatum and increased the size of Cymbidium etiolated stem and the number of node segments. The most conspicuous effects of the application of NO occurred after 30 days of treatment, increasing shoot elongation and number of node segments in C. fimbriatum and reducing these parameters in Cymbidium plants. With regard to ethylene and CO2 emission the different genera presented different responses. C. fimbriatum, Cattleya and Cymbidium showed increasing hormone liberation within the ethylene treatments. Furthermore, C. fimbriatum showed conspicuously higher ethylene and CO2 emission than Cymbidium plants. When incubated in the absence of light, the three orchid genera showed distinct behavior, separated into three groups: (1) etiolated stem formation only from SAM activity, and development of reduced leaves (Cymbidium) (2) etiolated stem formation from lateral buds and development of reduced leaves (C. fimbriatum), (3) absence of etiolated stems, with maintenance of foliar growth (Cattleya). (AU)