Altered feedback sensitivity of acetohydroxyacid synthase from valine-resistant mutants of tobacco (Nicotiana tabacum L.)

• Published in: Planta 1986-03, Vol.169 (1), p.46-50
• Main Authors: Relton, J.M. (Rothamsted Experimental Station, Harpenden (UK)), Wallsgrove, R.M, Bourgin, J.-P, Bright, S.W.J
• Format: Article
• Language: English
• Subjects: ACIDE AMINE; Agronomy. Soil science and plant productions; Allosteric regulation; AMINO ACIDS; AMINOACIDOS; Aminosaeure; Barley; Biological and medical sciences; Blatt; Cell lines; Classical and quantitative genetics. Population genetics. Molecular genetics; Classical genetics, quantitative genetics, hybrids; ENZIMAS; Enzymaktivitaet; ENZYME; ENZYMES; Fundamental and applied biological sciences. Psychology; Generalities. Genetics. Plant material; Genetic mutation; Genetics and breeding of economic plants; Genetics of eukaryotes. Biological and molecular evolution; Herbicides; Kinetics; METABOLISM; METABOLISME; METABOLISMO; MUTANT; MUTANTES; MUTANTS; Mutation; Nicotiana; NICOTIANA TABACUM; Plant cells; Plant growth regulators; Pteridophyta, spermatophyta; Stoffwechsel; VALINA; VALINE; Vegetals
• ISSN: 0032-0935; 1432-2048
• DOI: 10.1007/BF01369774

Acetohydroxyacid synthase (EC 4.1.3.18) has been extracted from leaves of three valine-resistant (Valr) tobacco (Nicotiana tabacum) mutants, and compared with the enzyme from the wild-type. The enzyme from all three mutants is appreciably less sensitive to inhibition by leucine and valine than the wild-type. Two of the mutants, Valr-1 and Valr-6, have very similar enzymes, which under all conditions are inhibited by less than half that found for the wild-type. The other mutant, Valr-7, has an enzyme that only displays appreciably different characteristics from the wild-type at high pyruvate or inhibitor concentrations. Enzyme from Valr-7 also has a higher apparent Km for pyruvate, threefold greater than the value determined for the wild-type and the other mutants. The sulphonylurea herbicides strongly inhibit the enzyme from all the lines, though the concentrations required for half-maximal inhibition of enzyme from Valr-1 and Valr-6 are higher than for Valr-7 or the wild-type. No evidence has been found for multiple isoforms of acetohydroxyacid synthase, and it is suggested that the valine-resistance of these mutant lines is the result of two different mutations affecting a single enzyme, possibly involving different subunits.