American Society of Plant Biologists (ASPB) Annual Meeting: Plant Biology 2012
The Orchidaceae is the most diverse family of flowering plants and is famous for its unusual and beautiful structural floral variation. It is distributed predominantly in rapidly disappearing tropical and sub-tropical forest ecosystems. Long-term seed storage banks can be a solution for threatened plant species but the stored seeds must tolerate extreme drying and cold. This ability is acquired during the last stage (maturation drying) of seed development and is correlated with a decline in water content and expression of the Late Embryogenesis Abundant (LEA) protein genes. Our goal is to investigate whether and when orchid seeds acquire desiccation tolerance during normal maturation and, if harvested prematurely, can be artificially induced to become desiccation tolerant. The specific aim of this work is to monitor changes in water content, germinability, desiccation tolerance and LEA protein gene expression in seeds undergoing natural ( in planta) and artificial drying in Phalaenopsis amabilis. The moisture content of fresh seeds drops quickly between 150DAP (when it is 70% moisture) and 165DAP (when it is 50% moisture), suggesting the onset of the maturation drying phase. Freshly harvested seeds can germinate as early as 90DAP but they are not capable of surviving desiccation (defined as the ability to germinate after drying to 5-10% moisture) until 170DAP. On the other hand seeds as young as 120 DAP can tolerate desiccation if they are slowly dried. During slow drying, seeds are placed in atmospheres of progressively lower relative humidity. During this time, seeds maintained their starting moisture content of 70% for 3 days, and then dried to 10-15% moisture on the 4th day. During this time, they acquired desiccation tolerance. Our results suggest that mature seeds of Phalaenopsis amabilis can tolerate desiccation and, if seeds are harvested prematurely, they can be rendered desiccation tolerant by appropriate post-harvest treatments.