Assembly of the Light-Harvesting Complexes During Plastid Development

Abstract

The light-induced assembly of functional components of the thylakoid membrane has been followed during the biogenesis of the wheat plastid. The levels of light-harvesting complex (LHC) apoproteins in the 30- to 18-kDa region increase rapidly upon exposure to continuous light (CL). The newly synthesized LHC II apoproteins appear to be present predominantly in the monomeric forms. Upon further greening the LHC II apoproteins are increasingly located in LHC II oligomeric forms. At the same time, during the first times of greening, the bands in the 20.5- to 19- and 17.5- to 15.5-kDa regions related to early light-induced proteins (ELIP) have been observed. Low-temperature fluorescence spectra (77 K) of chloroplasts isolated from intermittent light (IML)-grown leaves display a main emission band at 687 nm and a small one at 727 nm. As greening proceeds, the 727-nm peak gradually shifts to longer wavelengths and increases in intensity relative to the 687-nm emission peak. By 6 h, in seedlings transferred to CL, the fluorescence spectrum is characterized with bands at 687, 696, and 740 nm (main). The increase in fluorescence intensity at 740 nm takes place due to restoration of the energy transfer to the Chl a form at 710–712 nm from LHC I synthesized during CL.