Figure 4.

Lack of CURT1 Proteins Does Not Disturb Photosynthetic Complex Accumulation but Affects Photosynthesis Pleiotropically.

(A) The composition of thylakoid complexes from the wild type (Landsberg erecta [Ler]) and curt1 mutants was analyzed as in Figure 3A, except that aliquots corresponding to 5 µg chlorophyll were used. Antibodies specific for the PSII subunit CP43, cytochrome b₆ from the cytochrome b₆/f complex, the D subunit of PSI (PsaD), the γ-subunit of the chloroplast ATP synthase, NdhL from the NDH complex, and CURT1A were used. Ponceau Red (P.R.) staining served as the loading control.

(B) Immunoblot analysis of leaf proteins (corresponding to 40 µg of total protein) from the wild type (Col-0 and Landsberg erecta), curt1a-1 and curt1b-1 mutants, and mutants devoid of PSII (hcf136), PSI (psad1 psad2), cytochrome b₆/f (petc-2), or cpATPase (atpd-1). Antibodies specific for CURT1A, B, and C and the respective thylakoid multiprotein complexes, or actin as control, were used.

(C) Effective quantum yield (Φ_II), NPQ, and 1-qL (as listed in Supplemental Table 2 online) for wild-type and curt1 mutant plants are indicated on a gray scale.

(D) Time course of chlorophyll a fluorescence during illumination with actinic light at 100 μmol photons m⁻² s⁻¹. Average values ± sd (bars) for three to five different plants are indicated by closed (wild type) or open (curt1abcd) circles. Relative units (r.u.) are shown.

(E) Quantification of cyclic electron transport in situ. Increases in chlorophyll fluorescence were measured in ruptured chloroplasts after the addition of NADPH and Fd as described (Munekage et al., 2002). As controls, the mutants pgr5 (defective in Fd-dependent cyclic electron transport) and crr2 (defective in NDH-dependent cyclic electron transport) were employed.