Light-Dependent Chloroplast Development and Expression of a Light-Harvesting Chlorophyll a/b-Binding Protein Gene in the Gymnosperm Ginkgo biloba

Unlike conifers, the gymnosperm Ginkgo biloba is dependent on light for chlorophyll (Chl) synthesis and initiation of chloroplast development. Dark-grown seedlings show complete etiolation, including no detectable Chl accumulation, no leaf expansion, and increased hypocotyl elongation. When dark-grown seedlings are placed in white light, Chl synthesis and leaf expansion are initiated, but unlike angiosperms, which initiate rapid photomorphogenesis, Ginkgo takes at least 1 week to change to a normal light-regulated pattern of growth. A cDNA clone (pLhcb*Gb1) encoding a Chl a/b-binding protein of light-harvesting complex II from Ginkgo mRNA has been used as a probe for the expression of this family of mRNAs. We have found that, in common with angiosperms but in marked contrast to pines, Lhcb mRNA is expressed in a highly light-dependent manner. In addition to being expressed in light-grown leaves, this sequence is also expressed in the green tissues of immature seeds. The Lhcb mRNA appears during greening in parallel with the onset of Chl synthesis. The complete sequence of pLhcb*Gb1 has been determined and the deduced amino acid sequence was found to be of type I based on comparison with signature sequences of angiosperm and gymnosperm sequences.