Participation of acetolactate and acetoin producing system for chlorsulfuron-sensitivity in higher plants.

The properties of acetolactate and acetoin producing systems were studied using several plant species at different growth stages. The effects of herbicide chlorsulfuron on the correlation between these systems and plant growth were investigated, and the methods for determining acetolactate formed during the enzyme assay were evaluated.None of the plant species was inhibited in germination of seeds by chlorsulfuron. Growth and the acetolactate synthase (ALS) activity of rice and wheat were inhibited by chlorsulfuron, whereas growth of mungbean, soybean and azuki bean was not inhibited during the 4 days after germination. It was concluded that the chlorsulfuron-insensitivity of soybean depended on the contents of both ALS and acetoin forming enzyme: the content of ALS in soybean during the early days after germination was very low, whereas that of acetoin forming enzyme was very high. The enzyme which formed acetoin in soybean had optimum pH at 6 and this decreased with growth; ALS which had optimum pH at 7-8 began to increase from the 5 days after germination. The gas chromatographic method was used to determine acetolactate synthesized from pyruvate and acetohydroxybutyrate (AHB) synthesized from pyruvate and ketobutyrate during the enzyme assay. AHB synthesis in the enzyme assay was inhibited by chlorsulfuron at the same concentration as inhibited acetolactate synthesis. Acetolactate, acetoin and pyruvate were separated by high performance liquid chromatography using authentic compounds, but no acetolactate was present in a detectable amount in the enzyme reaction products.