Title: Bensulfuron Methyl Effects on Amino Acid and Protein Levels in Cultured Rice Cells.
Abstract: Effects of bensulfuron methyl (BSM) on amino acid and protein content were compared in normal and 10-5M BSM tolerant rice cells. Culture in the presence of BSM led to a dramatic decrease in the level of branched-chain amino acids to 25-49% of untreated in normal rice cells over 48hr, while they increased in BSM-tolerant cells. The other amino acids in exposed normal cells increased substantially, but those amino acids in tolerant cells changed relatively little. The inhibition of protein biosynthesis by BSM appeared to cause a decreased level of protein content in normal cells, while almost no effect in tolerant cells. The feedback inhibition by one or more of the end-products, valine, leucine and isoleucine, of acetolactate synthase (ALS) from normal and tolerant cells was also investigated. The activity of extractable enzyme from both cell types was feedback inhibited by the three amino acids Val+Leu, Val, Leu, Ile: 39, 41, 45, 58% of control at 5mM, but the enzyme of tolerant cells had less feedback sensitivity: 49, 55, 57, 80%, respectively. Based on these findings, a high level of branched-chain amino acid biosynthesis by the BSM-insensitively modified ALS and less sensitivity of the enzyme to branched-chain amino acids may provide protection against BSM in the tolerant cells.