Comparison of development and photosynthetic growth for filament clumps and regenerated microplantlet cultures of Agardhiella subulata (Rhodophyta, Gigartinales)

Abstract

Two axenic, in vitro liquid suspension cultures were established for Agardhiella subulata (C. Agardh) Kraft et Wynne, and their growth characteristics were compared. This study illustrated how reliable routes for the development of suspension cultures of macrophytic red algae of terete thallus morphology can be achieved for biotechnology applications. Undifferentiated filament clumps of 2-8 mm diameter were established by induction of callus-like tissue from thallus explants, and lightly branched microplantlets of 2-10 mm length were established by regeneration of filament clumps. The filament clumps were susceptible to regeneration. Adventitious shoot formation was reliably induced from 40% to 70% of the filament clumps by gentle mixing at 100 rev min-1 on an orbital shaker. The specific growth rate of the microplantlets was higher than the filament clumps in nonagitated well plate culture (4%-6% per day for microplantlets vs. 2%-3% per day for filament clumps) at 24°C and 8-36 μmol photons · m-2 · s-1 irradiance (10:14 h LD cycle) when grown on ASP12 artificial seawater medium at pH 8.6-8.9 with 20%-25% per day medium replacement. Oxygen evolution rate vs. irradiance measurements showed that relative to the filament clumps, microplantlets had a higher maximum specific oxygen evolution rate (P(o,max) = 0.181 ± 0.035 vs. 0.130 ± 0.023 mmol O2 · g-1 dry cell mass · h-1), but comparable respiration rate (Q(o) = 0.040 ± 0.013 vs. 0.033 ± 0.017 mmol O2 · g-1 dry cell mass · h-1), compensation point (I(c) = 3.8 ± 2.4 vs. 5.7 ± 1.2 μmol photons · m-2 · s-1), and light intensity at 63.2% of saturation (I(k) = 17.5 ± 3.9 vs. 14.9 ± 2. 6 μmol photons · m-2 · s-1). The microplantlet culture was more suitable for suspension culture development than the filament clump culture because it was morphologically stable and exhibited higher growth rates.