DEVELOPMENTAL-CHANGES IN AMOUNTS OF THYLAKOID COMPONENTS IN PLASTIDS OF BARLEY LEAVES

Changes in the amounts of several components of the photosynthetic electron-transport system during greening of etiolated barley leaves were studied on a "per plastid" basis. P700 and Q(A), which were initially absent from etioplasts, appeared 2 h after the start of illumination in complete complexes of PS I and PS II, respectively. From 6 h, they increased rapidly in amount with a constant stoichiometric ratio of 1 : 1. Amounts of Cyt f, Cyt b6, Cyt b-559 and FeS, initially present in etioplasts at levels that were one-third to half of those in mature chloroplasts, also increased rapidly after 6 h of illumination. The molar ratio of Cyt f, Cyt b6 and Cyt b-559 was the same in etioplasts and in mature chloroplasts, namely 1 : 2 : 2. After 4 h of illumination, levels of FeS increased at nearly the same rate as those of the PS I complex. The increase in levels of all components was marked after 6 h of illumination, probably due to the energy supplied by developing plastids that had just become photosynthetically competent. The results are discussed in relation to the time of appearance of chlorophyll-protein complexes and photochemical activities.