Figure 9.

The Effects of Irradiance on Chloroplast Development.

(A) Representative photographs showing cotyledons of wild-type and im plants germinated at 25°C and either 50 or 150 μmol photons m⁻² s⁻¹.

(B) The effect of growth irradiance on the proportion of green seedlings in im. 625 seedlings (25 per agar plate) were germinated in the dark for a period of 5 d and subsequently exposed to continuous irradiance of either 50 or 150 μmol photons m−2 s⁻¹ for 24 h at 25°C. The number of green versus either variegated or white cotyledons was scored visually. Letters represent statistically significant differences between means at the 95% confidence interval. Data represent the means ± se.

(C) Accumulation of chloroplast polypeptides in wild-type and im cotyledons as a function of time (h) during greening. Seeds were germinated in the dark for 5 d and subsequently exposed to CL of either 50 or 150 μmol photons m⁻² s⁻¹ for up to 24 h at 25°C. SDS-PAGE was performed using equal amounts of protein per lane. Immunoblots were probed with polyclonal antibodies raised against POR, Lhcb2, and RbcL as described in Methods.

(D) Relative expression level of PORA mRNA during greening of dark-grown wild-type and im cotyledons at either 50 or 150 μmol photons m⁻² s⁻¹ using qRT-PCR. The relative expression levels of mRNA in three replicate samples were normalized to Actin2, which served as the endogenous control, and were standardized to a calibrator sample consisting of mRNA from dark-grown wild-type seedlings (0 h) at both 50 and 150 μmol photons m⁻² s⁻¹, at 25°C. Data represent the means ± se.

(E) Relative expression level of PHYA mRNA during greening of dark-grown wild-type and im cotyledons at either 50 or 150 μmol photons m⁻² s⁻¹ using qRT-PCR. All conditions are identical to those described in (D). Data represent the means ± se.