Stoichiometries of photosystem I and photosystem II in rice mutants differently deficient in chlorophyll b

Stoichiometries of photosystem I (PSI) and photosystem II (PSII) reaction centers in a cultivar of rice, Norin No. 8, and three chlorophyll b-deficient mutants derived from the cultivar were investigated. Quantitation of PSI by photooxidation of P-700 and chromatographic assay of vitamin K₁ showed that, on the basis of chlorophyll, the mutants have higher concentrations of PSI than the wild-type rice. Greater increases were observed in the PSII contents measured by photoreduction of Q_A, binding of a radioactive herbicide and atomic absorption spectroscopy of Mn. Consequently, the PSIII to PSI ratio increased from 1.1-1.3 in the wild-type rice to 1.8 in chlorina 2, which contains to Chl b, and to 2.0-3.3 in chlorina 11 and chlorina 14, which have chlorophyll a/b ratios of 9 and 13, respectively. Measurement of oxygen evolution with saturating single-turnover flashes revelated that, whereas at most 20% of PSII centers are inactive in oxygen evolution in the wild-type rice, the non-functional PSII centers amount to about 50% in the three mutant strains. The fluorescence induction kinetics was also analyzed to estimate proportions of the inactive PSII in the mutants. The data obtained suggest that plants have an ability to adjust the stoichiometry of the two photosystems and the functional organization of PSII in response to the genetically induced deficiency of chlorophyll b.