Abscisic Acid-Induced Starch Accumulation in Bioenergy Crop Duckweed Spirodela polyrrhiza

Spirodela polyrrhiza, a fast-growing duckweed with high starch and low lignin content, shows promise as a feedstock for bioenergy. Abscisic acid (ABA) is a biological hormone that controls plant growth and stress response. The effects of different ABA concentrations (0, 1.0 x 10(-5), 1.0 x 10(-4), 1.0 x 10(-3), 1.0 x 10(-2), and 1.0 x 10(-1) mg/L) on duckweed biomass growth, carbon dioxide fixation, formation of photosynthetic pigments (Chlorophyll a (Chla), Chlorophyll b (Chlb), and carotenoids), the activities of soluble starch synthase (SSS) and starch branching enzyme (SBE), and the starch content of biomass were investigated in this study. ABA at concentrations lower than 1.0 x 10(-3) mg/L promoted carbon dioxide fixation, whereas it inhibited carbon dioxide fixation at concentrations over 1.0 x 10(-3) mg/L. ABA enhanced SSS and SBE activities at concentrations lower than 1.0 x 10(-2) mg/L. ABA treatment increased the content of Chla, Chlb, and carotenoids and resulted in the enhancement of starch content. Chla content gradually increased with the increasing concentration of ABA (1.0 x 10(-5) to 1.0 x 10(-2) mg/L). After culturing for 10 days, starch content in 1.0 x 10(-2) mg/L ABA medium reached 35.3% of dry weight (DW), which was the highest level in this study. This suggests that there is a great potential to develop a technology to increase starch accumulation in duckweed which can be used as an alternative to corn, sugarcane, or other food crops as a starch source.