Comparative Studies on Plastoquinones

Abstract

Changes of lipophilic chloroplast quinones in corn, oats, peas, and Vicia faba are reported after 0, 4, 8, 12, 16, 20, 24, 48, 72, or 96 hours of exposure to light. There is a pronounced increase in plastoquinone A and chlorophyll levels and slight increase, in plastoquinone C_1-6, vitamin K₁, and α-tocopherylquinone content. Coenzyme Q levels, on the other hand, show little change upon exposure to light. The sequence in which individual quinones appear during development is as follows: plastoquinone A instantaneously after exposure to light, plastoquinone C_1-6 from 4 to 24 hours, vitamin K₁ from 12 to 24 hours, α-tocopherylquinone from 0 to 24 hours of illumination. Small amounts (<0.01 μmole/g, dry wt) of plastoquinone A and plastoquinone B are found in seeds and etiolated tissues. After exposure to light, the quinone tentatively identified as a member of the plastoquinone B series by reverse phase thin layer chromatography disappears and can be detected again in small amounts during maturity and toward senescence of the leaf.