Fig. 4.

The impact of ABA on plastid differentiation in 7-day-old light-grown seedlings derived from seeds of plants grown under continuous light. (A) Characterization of the T-DNA insertion mutant cyp707a3. Transcripts of EX1, EX2, and CYP707A3 in WT (1), ex1/ex2 double mutant (2), and ex1/ex2/cyp707a3 triple mutant (3). Profilin 1 (PRF1) amplification was used as a control. (B) Size distribution of plastids in cotyledons of seedlings of WT (1), ex1/ex2 (2), and ex1/ex2/cyp707a3 (3). (C) Size distribution of plastids in cotyledons of WT and ex1/ex2 seedlings grown in the light on agar plates in the absence (-) or presence (+) of ABA (0.5 μM). Note that the average size of plastids in 7-day-old ex1/ex2 seedlings is larger than that in the 4-day-old seedlings shown in Fig. 1. (D) ABA-induced restoration of transcript levels of genes encoding plastid proteins that are suppressed in ex1/ex2 seedlings (Table S1D). Seeds were harvested from ex1/ex2 plants grown under continuous light and germinated in the dark for 2 days on agar plates in the absence or presence of ABA (0.2 μM). Transcript levels of 4 nuclear genes encoding plastid proteins (1, At1g14150; 2, At3g16250; 3, At3g63140; 4, At4g28750), 4 plastid genes (5, PsbB; 6, PsbD; 7, RbcL; 8, PsaA), and 3 control genes not affected by the ex1/ex2 mutations (9, At3g01790; 10, At5g60390; 11, At3g54280) were measured by real-time PCR using gene-specific primers and expressed relative to WT levels (-ABA). Values represent mean and SD of 3 independent measurements.