Figure 6.

C. reinhardtii CC1021 showed opposite taxis to a fixed source of exogenous abscisic acid (ABA) in the light and dark. Algal cultures were grown under a 16 h photoperiod to the mid log phase (A₇₅₀ = 0.3) growth stage and were sampled mid photoperiod. Fully dispersed samples of the algal culture were placed in open top 1.5 × 1.5 × 12 cm light-permeable acrylic troughs with a plug of agarose containing 1 mM ABA at the end indicated and were immediately placed horizontally either in the light (45 µmoles photons m⁻² s⁻¹) or the dark for 50 min. After incubation samples were simultaneously taken at incremental distances from the agar plug and their A₇₅₀ measured. Shown in (A) is a representative image indicating the positions attained by the algae immediately following the incubation period. The treatment-dependent relative cell densities at increasing distances from the agar plugs is shown in (B). Significant (P < 0.05 by χ² tests of goodness of fit) differences in the proportion of algal cells found at various distances from the ABA-containing agar plug between the light and dark incubations of the algae are indicated^(*).