Figure 3.

Exogenous abscisic acid (ABA) induced a negative geotropic movement response in C. reinhardtii CC-1021. Algal cultures were grown under a 16 h photoperiod to the mid log phase (A₇₅₀ = 0.3) growth stage and were sampled at (a) 1 h, (b) 8 h, (c) 15 h, (d) 20 h and (e) 23 h during a 24 h period where the 16 h photoperiod commenced at time = 0 h. Fully dispersed algal samples were placed in measuring cylinders +/−50 µM ABA to form 10 cm vertical culture columns and for 50 min were either illuminated from above with high-light (319.8 µmoles photons m⁻² s⁻¹) or placed in the dark. After incubation the A₇₅₀ at the depths indicated was measured and the relative cell density ratios at each depth were determined within each treatment. Shown are the mean data of n = 5 replicate experiments +/− the 95% confidence intervals around the mean in each case.