STOICHIOMETRIES OF PHOTOSYSTEM-I AND PHOTOSYSTEM-II IN RICE MUTANTS DIFFERENTLY DEFICIENT IN CHLOROPHYLL-B

Stoichiometries of photosystem I (PSI) and photosystem II (PSII) react ion centers in a cultivar of rice, Norin No, 8, and three chlorophyll b-deficient mutants derived from the cultivar were investigated. Quant itation of PSI by photooxidation of P-700 and chromatographic assay of vitamin K-1 showed that, on the basis of chlorophyll, the mutants hav e higher concentrations of PSI than the wildtype rice, Greater increas es were observed in the PSII contents measured by photoreduction of Q( A), binding of a radioactive herbicide and atomic absorption spectrosc opy of Mn. Consequently, the PSII to PSI ratio increased from 1.1-1.3 in the wild-type rice to 1.8 in chlorina 2, which contains no Chi b, a nd 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 w ith saturating single-turnover flashes revealed that, whereas at most 20% of PSII centers are inactive in oxygen evolution in the wildtype r ice, 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 stoichiomet ry of the two photosystems and the functional organization of PSII in response to the genetically induced deficiency of chlorophyll b.