Figure 4

In the absence of light exogenous abscisic acid (ABA) failed to induce a negative geotropic movement in the C. reinhardtii mutant strains CC-477 and CC-2492 that lack functional flagella. Algal cultures of the mutant strains were grown under a 16 h photoperiod to the mid log phase (A₇₅₀ = 0.3) growth stage and were sampled 1 h into the photoperiod. Fully dispersed algal samples were placed in measuring cylinders +/−50 µM ABA to form 10 cm vertical culture columns and for 50 min were incubated 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 in (A) are the means of data from n = 4 replicate experiments for each mutant +/− the 95% confidence intervals around the means in each case. Shown in (B) is a representative image of the positions attained by the algae immediately following the period of incubation.