A, Northern-blot analysis of the expression of genes involved in pigment
synthesis and light harvesting during chloroplast differentiation of tobacco
seedlings under various light intensities. Four-day-old etiolated seedlings
were exposed to continuous white light of LL (10 μmol
m–2 s–1; gray box) or
ML (100 μmol m–2 s–1; white box) intensity for different time
periods (0, 3, 5, 8, 12, and 24 h). Gel-blot analysis was performed after
separation of total RNA extracted from the individual samples (minimum of 60
seedlings each). For hybridization, nonradioactively labeled DNA fragments of
the various xanthophyll biosynthetic genes were used as probes. bhy,
β-carotene hydroxylase; zep, zeaxanthin epoxidase; vde,
violaxanthin de-epoxidase; cab, chlorophyll a/b binding protein of
LHC II; and ET, etiolated seedlings. Bottom, 25S rRNA hybridization for
verification of gel loading. B, Densitometric scan of mRNA patterns of the
β-carotene gene during chloroplast differentiation of tobacco seedlings.
Signals were normalized with respect to the rRNA. The value for etiolated
seedlings was set to 1. n = 3.