Abstract
The nuclear gene mutants M134 and M249 that accumulate chlorophyllides esterified with incompletely reduced alcohol were isolated from rice plants (Oryza sativa L.). On HPLC analyses to plant quinones, methylnaphthoquinones varying in the reduction state of the side chain (menaquinones) were clearly detected in leaf segments of the rice mutants. By measurements of the pool of plant quinones, we showed that the synthesis of α-tocopherol is suppressed in developed leaves of mutants, due to insufficient availability of phytol (P) which is formed by reduction of geranylgeraniol. On the other hand, photosynthesis in mutants occurred without reduction of side chain to P, but the P moiety is required to prevent leaves from chlorosis under light-stressed conditions. From measurements of chemical redox of P700 in mutant thylakoid membranes and leaf photosynthetic activity, hydrogenation of the side chain in phylloquinone is not essential to achieve the activity of photosystem I.
