PLANT PHYSIOLOGY , Vol 101, Issue 1 227-236, Copyright © 1993 by American Society of Plant Biologists
Light-Induced Biogenesis of Light-Harvesting Complex I (LHC I) during Chloroplast Development in Barley (Hordeum vulgare) (Studies Using cDNA Clones of the 21- and 20-Kilodalton LHC I Apoproteins)
S. Anandan, D. T. Morishige and J. P. Thornber
Department of Biology, University of California, Los Angeles, Los Angeles, California 90024-1606
The light-harvesting complex (LHC) Ib pigment-proteins form the major
component of the LHC I complex in higher plants. They comprise chlorophylls
a and b, xanthophylls, and at least two polypeptide subunits of 21 and 20
kD in barley (Hordeum vulgare). We have identified two cDNA clones, LHC
Ib-21 and LHC Ib-20, encoding the 21- and 20-kD LHC Ib apoproteins,
respectively. N-terminal protein sequences of the purified LHC Ib
polypeptides were used for the unequivocal correlation of these clones to
their respective apoproteins. The cDNA clones encode two proteins that have
strong sequence similarity to other LHC I and LHC II pigment-binding
polypeptides of photosystems I and II. The 21-kD polypeptide contains 201
amino acid residues (22.14 kD), and the 20-kD polypeptide contains 200
amino acid residues (22.18 kD). The biogenesis of the LHC Ib apoproteins
and the pigmented LHC I during the light-induced development of the
chloroplast was studied. Accumulation of the two LHC Ib mRNAs is induced by
light, and their amount is regulated by phytochrome. LHC Ib polypeptide
accumulation in the thylakoid membrane temporally lags behind transcript
accumulation. The rates of accumulation of LHC Ib transcripts and of their
apoproteins lag behind those of the major LHC II component, LHC IIb.
Complete assembly of the LHC Ib pigment-protein, as observed by
low-temperature fluorescence spectroscopy, requires exposure of dark-grown
seedlings to 72 h or more of light.