Physiological effects of photosystem II-herbicides on the development of the photosynthetic apparatus.

Photosystem II-herbicides (bentazone*, diuron) not only block photosynthetic electron transport, but have additional effects on the cell metabolism of Raphanus seedlings. They induce the formation of shade-type chloroplasts with a different ultrastructure and prenyllipid composition. This is shown by higher grana stacks as well as by higher chlorophyll b and lutein amounts with reference to chlorophyll a, and lower levels of the plastidic prenylquinones (plastoquinone, phylloquinone, α-tocoquinone) and β-carotene as compared to the controls.The two herbicides bentazone and diuron change the labelling pattern of the chloroplast pigments from (3)H-mevalonic acid and 2-(14)C-acetate and also reduce the accumulation of anthocyanin (pelargonidin), which is a further indication of a shade-type growth response. The level of ubiquinone, an indicator for mitochondrial activity, is, however, increased.