Figure 1.

Exogenous abscisic (ABA) acid differentially altered HCO₃⁻ uptake by C. reinhardtii in a light-intensity-dependent manner. Mid log phase (A₇₅₀ = 0.3) algal cultures were immobilised in alginate gel beads containing the concentrations of ABA indicated and in (A) were incubated for 1 h under different light intensities (7.6 to 223.2 µmoles photons m⁻² s⁻¹) with bicarbonate indicator buffer in TAP media. Depletion of HCO₃⁻ in the media was monitored as the change in absorbance in the indicator buffer at 550 nm after the incubation period with conversion to the change in the concentration of HCO₃⁻ in the TAP media by reference to a standard calibration. Shown are the mean δHCO₃⁻ (mM) h⁻¹ of n = 5 replicates with errors as the 95% confidence intervals around the means in each case. In (B) mid log phase (A₇₅₀ = 0.3) algal cultures were sampled 1 h into the photoperiod and subsequently exposed for 1 h to the different light intensities indicated. Algal cells were pelleted from n = 3 replicate 25 mL aliquots of culture. Pellets were extracted and assessed for ABA content by competitive ELISA (MyBioSource Inc.). Data are shown as the mean ABA content cell⁻¹ with error bars shown as +/− the 95% confidence interval around the mean in each case.