Immunological Quantification of Proteins Related to Light-Harvesting Chlorophyll a/b Protein Complexes of the Two Photosystems in Rice Mutants Totally and Partially Deficient in Chlorophyll b

Ten rice chlorina mutants of Type I, which totally lack chlorophyll b and hence are unable to synthesize light-harvesting chlorophyll a/b protein complexes of photosystem II (LHC-II), contained mRNA for proteins related to LHC-II. Immunoblotting with an antiserum, which had been raised against the 24 and 25 kDa apoproteins of LHC-II and found to cross-react with the 26 kDa protein of LHC-II and the 20 and 21 kDa apoproteins of light-harvesting chlorophyll a/b protein complexes of photosystem I (LHC-I), revealed that all the five proteins related to LHC-Iand LHC-II were present in reduced amounts in the Type I mutants. Three Type HA mutants, which have a chlorophyll a/b ratio of 10, were more abundant in the apoproteins, while three Type IIB mutants with the ratio of 15 were heterogeneous in terms of the apoprotein content. All the chlorina mutants contained less P700 compared with the wild type rice, but were relatively more abundant in the LHC-I proteins than the LHC-II proteins. The results show that all the rice chlorina strains are mutants of chlorophyll b synthesis and the deficiency of chlorophyll b differently affects accumulation of the apoproteins of LHC-I and LHC-II. To balance light absorption between the two photosystem, loss of LHC-II is partly counter-balanced by a decrease in the number of PSI complexes in the mutants.