Fig. 6.

Phycobilisome turnover in CpcD mutants during chlorosis. A, Comparison of phycobilisome absorption (625 nm) in CpcD^Ala or CpcD^Asp mutants and the wild-type during vegetative growth and during chlorosis. Shown are average values from three independent replicates at light intensities below 25 μm photons m⁻² s⁻¹ during the progression of chlorosis. Error bars indicate standard error of mean. B, Determination of minimum fluorescence (F₀) ratios of CpcD mutants and the wild-type during chlorosis relative to that during vegetative growth (reference). F₀ fluorescence yields were recorded during chlorosis by PAM fluorometry of three independent replicates (the same cultures as in panel A). Ratios of average values to the reference (wild-type F₀ during vegetative growth; defined as 100%) are indicated. Error bars indicate standard error of mean. Significant differences (p ≤ 0.05) between the wild-type and mutants are indicated by *; n.s. indicates nonsignificant differences. C, Measurement of the PSII-phycobilisome quantum yield by PAM fluorometry at increasing light intensities during exponential growth and after 12 d of chlorosis. Error bars indicate standard error of mean, n = 3.