Photochemical apparatus organization in the thylakoid membrane of Hordeum vulgare wild type and chlorophyll b-less chlorina f2 mutant

The stoichiometry of the electron-transport complexes and the chlorophyll (Chl) antenna size of the photosystems is correlated in chloroplasts from barley wild type and in the chlorophyll b-less chlorina f2 mutant. Chloroplasts from mutant plants displayed three characteristic changes in the organization of Photosystem I (PS I) and Photosystem II (PS II). (a) The light-harvesting antenna of PS II was lowered from about 250 Chl a + b in the wild type to only 50 Chl a molecules in the mutant. The light-harvesting antenna of PS I was lowered from about 185 Chl a + b in the wild type to about 150 Chl a molecules in the mutant. (b) The PS IIPS I complex ratio was substantially higher, i.e., about 3.0, in the mutant vs. about 1.8 in the wild type. (c) Mutant chloroplasts lacked the differentiation of PS II into PS IIα and PS IIβ. The enhanced PS IIPS I ratio is explained as a response of the plant to the lowered light-harvesting capacity of PS II in the mutant chloroplasts. The apparent lack of PS II heterogeneity in the thylakoid membrane of the chlorina f2 correlates with the absence of the Chl ab light-harvesting complex II (LHC II) (Percival, M.P., Webber, A.N. and Baker, N.R. (1984) Biochim. Biophys. Acta 767, 582–589) and suggests a difference in the amount of LHC II associated with PS IIα and PS IIβ.