In intersubgeneric crosses of diploid evergreen azaleas (EV) × diploid Rhododendron japonicum f. flavum (JP), many progenies become albino as a result of plastome-genome incompatibility between a plastid genome from EV and a nuclear genome from JP. To clarify the mechanism of the incompatibility, inter-and intra-ploid crosses of diploid (2x) EV × diploid (2x) JP, tetraploid (4x) EV × tetraploid (4x) JP, 2x EV × 4x JP, and 4x EV × 2x JP were conducted. Seeds were obtained in all crosses, although the number of progenies per capsule was relatively low in crosses with 4x JP as a pollen parent. Plastome-genome incompatibility between a plastid genome from EV and a nuclear genome from JP was observed in progenies from 2x EV × 2x JP, 4x EV × 4x JP, and 2x EV × 4x JP, but not in 4x EV × 2x JP. This result indicates that plastome-genome incompatibility was broken by relative increase of the genome from EV in the nuclear genome of progenies.

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Aggregatibacter actinomycetemcomitans is an oral pathogen for aggressive periodontitis, and encodes a triheme c-containing membrane-bound enzyme, quinol peroxidase (QPO) that catalyzes peroxidase activity using quinol in the respiratory chain. In the previous work, we have characterized recombinant QPO purified from the membrane fraction of Escherichia coli harboring a plasmid containing QPO gene. Irreversible inactivation of QPO by high concentration of H2O2 exhibited pseudo-first order kinetics. Analysis of initial-rate kinetics of QPO may suggest that enzyme catalytic mechanism is explained by a Ping Pong Bi Bi system rather than sequential systems. In addition, the redox reactions of cytochrome c in the presence of several values of [Q1H2]/[Q1] were at equilibrium, and only about 2/3 of the cytochrome c of QPO is reduced at high ratios of [Q1H2]/[Q1]. These results indicated that one of the three heme c moieties of QPO is maintained in an oxidized form even at increased ratios of [Q1H2]/[Q1], suggesting that QPO is reduced in the absence of H2O2 and only two of the three heme c moieties are reduced in the presence of high concentration of the Q1H2. Product inhibition of QPO accorded with our theoretical model for the reaction mechanism. Considered together, the enzymatic kinetics data for QPO confirm the Ping Pong Bi Bi system.