| Abstract: | Endogenous levels of indole-3-acetic acid were mesaured in synchronous cultures of Chlorella pyrenoidosa (TX-7-11-05). The cultures were synchronized by alternating light:dark periods of 15:9 hr at a temperature of 40 ± 1 C. After 2 synchronous cycles the cultures were exposed to a low light treatment of 350 ± 100 ft-c. The time to incipient cell division under these conditions was 6 hr and 15 min. Samples were taken at 3 sampling periods during the low light treatment period:low light 0 hr (LL0); low light 3 hr (LL3); and low light 6:15 hr (LL6:15). The algal extracts were analyzed by a fluorometric procedure which measured the indole-α-pyrone product formed by the action of the trifluoracetic acid-acetic anhydride reagent with IAA. The IAA levels increased gradually from the autospore stage (5.19 μg × 10?4/mg dry wt) to the adolescent stage (7.13 μg × 10?4/mg dry wt) and more rapidly when approaching the ripened adult stage (14.55 μg × 10?4/mg dry wt). The mean percentage increase from autospore to adolescent was 36.9%, and from adolescent to ripened adult 104.6%. The total percentage increase from autospore to adult was 180.3%. Levels of IAA were 2 times higher just prior to division than in the autospore stage. |
