Figure 4.

pgdh3 mutants show pronounced acceptor side limitation and altered pmf partitioning. Chlorophyll-a fluorescence was recorded with a slow light response curve on dark-adapted WT and pgdh3 plants. A, No changes were found in ETRII or in the fraction of oxidized Q_A (qL). NPQ in mutants was lower at light intensities above 400-μmol photons m⁻² s⁻¹. B, P₇₀₀ parameters were measured on plants taken directly from the controlled environment chamber and deconvoluted from difference absorbance signals arising from plastocyanin. The electron transfer rates of PSI (ETRI) in both pgdh3 lines were slightly decreased. PSI was by trend less donor-side limited (Y(ND)) in pgdh3 when actinic light exceeded 500-μmol photons m⁻² s⁻¹. Independent of the light intensity pgdh3 revealed significantly stronger acceptor side limitation (Y(NA)). C, Neither the cytochrome-f oxidation level nor the proton conductivity of the thylakoid membrane (gH⁺) were altered at three different light intensities. While the total pmf size (ECS_T) was not different among genotypes (transparent bars), both pgdh3 mutant lines showed much stronger ΔΨ partitioning at low (88) and ambient (144-μmol photons m⁻² s⁻¹) actinic light (solid bars). Data represent mean values (±sd) of nine independent samples. Letters indicate significantly different values between WT and the individual pgdh3 mutant lines as determined by ANOVA (p < 0.05), with (a) indicating significant differences from the WT, (b) indicating significant differences from both WT and pgdh3-2, and (c) indicating significant differences from both WT and pgdh3-1. For the pmf panel, the upper row indicates significant differences of ECS_T, while the lower row indicates significant differences of ΔΨ. To clarify which letter refers to ECS_T or ΔΨ, in this panel, also nonsignificant statistical results are indicated by a horizontal line.