Fourteen-day-old, light-grown Arabidopsis Col-0 wild-type plants were incubated in buffer without (-) or with 1 mM ALA (+) in darkness (D) for the indicated times. Samples were harvested prior to treatment (t0) and at 4 hr and 24 hr after the onset of treatment. (A) Western blot analysis of proteins involved in tetrapyrrole biosynthesis (GluTR1/2, GBP, CHLI, GUN4, CHLM, CHL27, YCF54, FC1, and FC2), Clp protease (ClpS and C) and components of the photosynthetic electron transfer chain (LHCA1, LHCB1, PetB, PsaL). t(0) = sample harvested from light-grown seedlings prior to ALA treatment. Signal intensities for GluTR1 relative to t(0) are shown at the top. (B – D) Levels of chlorophylls (Chl) a and b (B), non-covalently bound (ncb) heme (C) and protochlorophyllide (Pchlide) (D) found in control and ALA-treated seedlings. Data are given as means ± sd (n = 4). (E – J) qRT-PCR analysis of HEMA1 (coding for glutamyl-tRNA reductase 1), HEMA2 (GluTR2), GSA1 (glutamate-1-semialdehyde 2,1-aminomutase 1), CHL27 (a subunit of aerobic cyclase) and FC1/2 (ferrochelatase 1 and 2) mRNAs. Data are given as means ± sd (n = 4). The lowercase letters in panels (B – J) indicate statistical groups determined by Student’s t-test (p<0.05).